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Portion size and food intake1
8 Portion size and food intake1 B. Rolls, J. Ello-Martin and J. Ledikwe, The Pennsylvania State University, USA
8.1 Introduction: the growth in portion sizes Obesity is a rapidly growing, world-wide public health problem. In recent decades, there has been a significant increase in the prevalence of obesity. The World Health Organization estimates that globally there are over 1 billion adults and 17 million children who are overweight or obese (World Health Organization, 2004). It is unlikely that our biology could have changed in several decades, so other explanations for this surge in obesity rates must be found. One possible reason for the increase is that the environment in Westernized societies has altered, so that overconsumption of energy has become easier. At the same time, opportunities for physical activity have declined. Thus, it is increasingly difficult for individuals to match energy intake to energy output in order to maintain a healthy body weight. Some of the changes in the eating environment that encourage overeating are the increasing availability of inexpensive high-energy-dense (kJ/g) foods, the wide variety of palatable foods, the increasing frequency of meals consumed outside of the home, and the rise in portion sizes. While all of these changes may stimulate excess intake, we will present data suggesting that large portion sizes, particularly of energy-dense foods, are contributing to the epidemic of obesity, and we will present constructive measures that could help to improve the eating environment.
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Supported by NIH grants R37DK039177 and R01DK059853.
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8.1.1 Increasing portion sizes Studies of food portions offered at fast food outlets, chain restaurants, and convenience stores indicate that portion sizes of many items have increased (Young and Nestle, 2002). According to Nestle (2003), this trend began in the USA as early as the 1970s, with portion sizes increasing sharply in the 1980s and continuing to rise. Data from Denmark show similar trends (Matthiessen et al., 2003).The growth of portion sizes has been most evident in fast food restaurants where the ‘supersizing’ of some menu items is relatively common (Harnack et al., 2000). Items available at fast food restaurants are estimated to be two to five times larger than two decades ago (Young and Nestle, 2003). In general, food packaging and common portion sizes of popular dishes are 25% larger in the USA than in France where rates of obesity are lower (Rozin et al., 2003). With the availability of many foods in larger sizes, it is not surprising that epidemiological studies indicate people are consuming larger portions of food (Smiciklas-Wright et al., 2003).
8.2 Studies showing that portion size affects energy intake 8.2.1 Adults Although the increase in the size of portions and the prevalence of overweight and obesity have occurred in parallel, a crucial step in assessing a causal relationship between portion size and obesity is to determine experimentally whether portion size affects energy intake. Recent controlled studies clearly show that portion size does affect energy intake. When we tested how adults responded to four different portions of macaroni and cheese served on different days, we found that the bigger the portion, the more participants ate (Rolls et al., 2002). They consumed 30% more energy (676 kJ) when offered the largest portion (1000 g) compared to the smallest portion (500 g). The effect was seen both when the portion on the plate was determined by the investigator and when the participants served themselves from bowls containing different size portions. Of particular interest was the finding that, despite the difference in intake, participants reported similar ratings of hunger and fullness after eating. The results were not affected by subject characteristics including sex, body mass index, or concern about food intake or body weight. After the study was over, less than half (45%) of the subjects reported noticing that there were differences in the portions served. It is surprising that, in a controlled laboratory setting where the main focus was food and eating, many participants in the study appeared to be unaware of the changes in the amount of food offered and the subsequent effect on their intake, hunger, and satiety. It seems likely that, when individuals are in situations where there are more distractions, such as when eating out, they would be even less aware of portion size.
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It could be argued that the effects of portion size on intake are specific to foods like macaroni and cheese that are amorphous or have no defined shape. The portion size of such foods has been shown to be particularly difficult to judge, especially when the portions are large (Slawson and Eck, 1997). We conducted further studies to test whether intake can also be influenced by the portion size of other types of foods, such as those with clearly defined shapes or units. People tend to eat in units. That is, if they are offered a food that comes in a preportioned unit, such as a cookie, most people will eat the whole cookie (Siegel, 1957). One of the most common unit foods is the sandwich. In most fast food establishments there is a choice of sandwich sizes; often the larger sandwiches are purchased because the consumers perceive them as better value in that they get more food for their money (National Alliance for Nutrition and Activity, NANA, 2002). A key question is, if consumers choose a larger sandwich, are they likely to eat more? To test this, on four different days, we offered men and women submarine sandwiches that varied in size: 6, 8, 10, and 12 inches (15, 20, 25, 30 cm) (Rolls et al., 2004e). We found a systematic and significant effect of portion size on intake for both men and women (Fig. 8.1). When served the 12-inch sandwich compared to the 6-inch sandwich, women consumed 31% more energy (665 kJ) and men consumed 56% more energy (1485 kJ). Ratings of hunger and fullness after lunch did not differ significantly when subjects were served the 8-, 10-, and 12-inch (20-, 25-, 30-cm) sandwiches, despite the increase in energy intake. It appears that, when served bigger portions, consumers override or adjust their level of satiety to accommodate greater energy intakes.
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Fig. 8.1 On separate days, adults were served a 6-, 8-, 10-, or 12-inch sandwich for lunch. For both men (n = 38) and women (n = 37), energy intake increased as sandwich size increased. Within each sex, means with different letters are significantly different (P < 0.025).
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The amount of food in a package or container may also influence how much is eaten. Some prepackaged foods come in a wide variety of sizes; for example, bags of potato chips range from 28 g single-serving bags to 560 g family-size bags. To test how the size of the bag affects intake, on five occasions we served men and women an afternoon snack that consisted of 28, 42, 85, 128 or 170 g of potato chips in a plain, unlabelled foil bag (Rolls et al., 2004b). Participants ate directly from the bag so that they had few visual cues to guide consumption. The results showed that portion size had a significant effect on snack intake for both the men and the women (Fig. 8.2). For example, when served the 170 g package, women ate 18% (200 kJ) more and men ate 37% (511 kJ) more than when served the 85 g package. As subjects increased their snack intake with increasing package size, they also reported feeling fuller; however, they did not adjust their intake at the subsequent dinner meal to compensate for the increased energy intake and fullness. Thus, bigger portions of a prepackaged snack increased energy intake in the short term. It is not clear that all prepackaged foods will have a similar effect. It is possible that the effect will be greatest for highly palatable foods, such as chips, that people find difficult to stop eating. Additional studies conducted in a variety of situations confirm that the package or container size of a variety of foods can affect how much food
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Fig. 8.2 At a mid-afternoon snack on different days, men (n = 26) and women (n = 34) were offered one of five package sizes containing different portions of potato chips (crisps). Both men and women increased their intake of chips as the package size increased; furthermore, subjects did not significantly adjust their intake at dinner for the excess energy consumed with the snack. Means within each sex with different letter are significantly different (P < 0.02).
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is prepared and eaten (Wansink, 1996). When women were given a 2 lb box of spaghetti and asked to take out enough to make a dinner for two, they removed an average of 302 strands. But when given a 1 lb box, they removed only 234 strands. When frying chicken, women poured 4.3 ounces (126 ml) of cooking oil from a 32-oz bottle, but only 3.5 ounces (103 ml) from a 16oz bottle. When people were asked how many chocolate candies they would eat while watching a movie by themselves, participants poured 63 from a small package that contained 114 candies, 103 from a package double in size, and 122 from a package triple in size. That is, they poured about twice as much from a jumbo bag, a difference of about 1046 kJ (Wansink, 1996). In a cinema, consumers were given either a medium (120 g) or large (240 g) bucket of popcorn. Subjects rated the taste of the popcorn, and were divided into two groups depending upon whether they perceived the taste as favorable or unfavorable. The results showed an effect of the portion size of popcorn on intake regardless of how the taste of popcorn was rated (Wansink and Park, 2001). Thus, it is not just the palatability of foods that is driving intake up when large portions are available. A number of controlled studies show that both in the laboratory and in more naturalistic settings, the portion size and package size of a variety of foods can affect energy intake in adults in the short term. It is possible that, after a bout of overeating stimulated by large portions, compensatory mechanisms will limit subsequent intake. We tested this in a study in which the portion size was increased for all foods served to men and women over a 2-day period (Rolls et al., in press). The results showed a significant effect of portion size on energy intake over the 2 days. When the portions of all foods were doubled, energy intake on both days increased for all subjects by a mean of 26% (2218 kJ/d for women and 3402 kJ/d for men) (Fig. 8.3). Although subjects reported feeling more full after they consumed the larger portions, they did not compensate for the excess energy eaten over the course of the first day by reducing their intake on the second day. Thus, these results show that the effects of portion size can persist over several days and are associated with significant increases in daily intakes. Studies of longer term effects of portion size on energy intake are in progress.
8.2.2 Children While it has been clearly shown that adults respond to increasing portions by eating more, they probably did not start life responding in this way. A recent analysis of food survey data over a 20-year period indicates that, despite changes in the eating environment, there has been remarkable stability in the average portion size of foods consumed by children in the second year of life (McConahy et al., 2002). A controlled laboratory study that we conducted confirms that, in young children, intake is relatively unaffected by environmental cues such as portion size. When we fed 3-year-olds three different portions of macaroni and cheese at three separate lunches,
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Fig. 8.3 Cumulative energy intakes (mean ± SEM) by condition of portion size (100, 150, 200%) of all foods consumed for men (n = 16) and women (n = 16) over 2 consecutive days. B, breakfast, L, lunch, D, dinner, S, snack. The effect of portion size on energy intake persisted over 2 days. Means within each sex with different letters are significantly different.
they ate the same amount at each meal. Their intake was therefore unaffected by portion size. In contrast, 5-year-old children responded as adults do, in that they ate significantly more as the portions increased. This response to portion size occurred even though their hunger did not differ at the start of the meals (Rolls et al., 2000). Similarly, Fisher and colleagues (2003) found that 4-year-old children ate 25% more when they were served an entrée that was twice the size of an age-appropriate portion. In this study, the children who increased their intake the most when served large portions were those who had been identified as more likely to eat in the absence of hunger. It is not clear why children are more influenced by portion size as they age. Data suggest that early experiences lead to the development of behaviors that shape eating habits. In one study, 4-year-old children who were rewarded for cleaning their plates increased their energy intake. On the other hand, children who were taught to focus on satiety cues, indicated by the fullness in their stomachs, ate an appropriate amount of food (Birch et al., 1987).Thus, the response to portion size by children could be a learned behavior which leads to a shift of attention away from internal hunger and satiety cues toward food cues in the external environment. A lack of response to satiety signals may predispose children to overeat in an environment in which large portions of palatable foods are readily available (Barkeling et al., 1992; Birch and Fisher, 1998).The influence of large portions on intake, however, has been shown to be moderated simply by allowing children to serve themselves. One study demonstrated that children ate 25% less of a large entrée when they decided for themselves how much
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food to put on their plates, compared to when they were served the large portion of the entrée by an adult (Fisher et al., 2003).
8.3 Eating out and portion size Although there is some evidence that portions consumed at home are increasing (Nielsen and Popkin, 2003; Young and Nestle, 2002), the large portions served in restaurants may be a bigger problem for weight management. The increase in the prevalence of obesity since the 1970s coincides with an increase in the number of meals eaten outside the home (Harnack et al., 2000; Lin et al., 1999). Today, Americans are 40% more likely to consume meals from restaurants three or more times a week as they were in the late 1980s (Kant and Graubard, 2004). A number of studies indicate that meals consumed away from home have a lower diet quality and are higher in energy than at-home foods (Bowman et al., 2004; Clemens et al., 1999; French et al., 2001; Kant and Graubard, 2004; Paeratakul et al., 2003). Furthermore, in both adolescents and adults, the frequency of eating out is associated with an increase in energy and fat intake (Clemens et al., 1999; French et al., 2001; Kant and Graubard, 2004). For example, women who eat out frequently (more than six times a week) have been shown to have daily energy intakes approximately 1200 kJ higher than those who eat at restaurants less often (Clemens et al., 1999). In addition to high energy intakes, data show a relationship between eating out and weight status (Binkley et al., 2000; Cho et al., 2003; French et al., 2000; Kant and Graubard, 2004; McCrory et al., 1999). Nationally representative data indicate that the proportion of food consumed from fastfood restaurants is positively associated with body mass index (BMI) in both men and women (Binkley et al., 2000). One prospective study found that, over 3 years, an increase in the frequency of fast food consumption was associated with an increase in body weight (French et al., 2000). The high availability of large portions of energy-dense foods in restaurants may provide an explanation for the association between eating out and increased body weight. A cross-cultural analysis revealed that the portion sizes of popular restaurant dishes were 25% larger in the USA than in France, a country with substantially lower rates of obesity (Rozin et al., 2003). Restaurants have found that customers appreciate good value, and this translates into large portions at a low price. Since food is only a small percentage of the cost of a restaurant meal, giving customers more food is an excellent economic strategy if it increases total sales. This is possible because agricultural subsidies have helped to reduce the cost of some foods and commodities, such as vegetable oil and sugar, which have become very inexpensive (Drewnowski and Specter, 2004; Nestle, 2003). Thus the practice of ‘supersizing’ (giving customers a lot more food and energy for
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only a small additional cost) is widespread, particularly in fast food establishments. Restaurants may be giving consumers what they want in terms of value, but a crucial issue is whether people can adjust their energy intake to their energy needs when tempted with large portions of energy-dense, palatable foods. The American Institute of Cancer Research has provided data that offer insight into how individuals view portion size when dining out (American Institute for Cancer Research, 2003). In a survey of more than 1000 adults, 69% indicated that, when dining out, they finish their entrées all or most of the time. Of those adults, 30% reported that they would have been satisfied with a smaller portion. This suggests that, when eating out, many adults ignore satiety signals and eat beyond the point of noticeable fullness. Additionally, a number of survey respondents (42%) reported that they determine the amount of food to eat according to what they are used to eating. Thus, the portion sizes that individuals customarily eat may be related to frequent exposure to large portions over time. A recent study demonstrates that the portions served in restaurants can directly affect how much is eaten. We tested how increasing the portion size of a popular dish, while keeping the price the same, would affect intake in a restaurant setting (Diliberti et al., 2004). An entrée, baked ziti, was offered ten times over 5 months and 180 adult customers purchased the dish during that period. On different days, the portion was varied between a standard portion (248 g, 1766 kJ) and a large portion (377 g, 2647 kJ). Results showed that portion size had a significant impact on intake, such that mean intake of the standard portion was 1671 kJ and of the larger portion was 2390 kJ. Thus when customers were served 50% more they ate 43% more, equivalent to 719 kJ. A survey filled out by the customers showed no difference in ratings of the appropriateness of the two portions. Thus, in restaurants as well as in the laboratory, portion size has a significant impact on energy intake, and it is likely that the consumers are often unaware of this effect.
8.4 Portion size, energy intake and obesity When eating out, portion size is one of a number of variables that could affect consumption. Having a wide variety of palatable foods, eating in a convivial atmosphere with friends, and the consumption of alcohol may also increase energy intake. The high energy density (kJ/g) of restaurant meals is likely to promote excess intake. A systematic series of studies indicates that individuals consistently consume more energy when presented with foods having a higher energy density than with similar foods having a lower energy density (Bell et al., 1998; Rolls et al., 1999a,b). Prentice and Jebb (2003) recently compiled the energy density values of foods from wellknown fast food outlets in Britain, finding that the energy density of the entire menu (beverages were not included) from these restaurants was
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12.0 kJ/g. Further work is needed to determine the average energy density of fast food meals and to examine the influence of the new, popular salad options on meal energy density at these establishments. For comparative purposes, the energy density of the US diet, based on all foods consumed over two days, was found to be 7.8 kJ/g (Ledikwe et al., 2005). The relatively high energy density of fast food can facilitate the overconsumption of energy. For example, when served a fast food meal with extra large portions in a food court, adolescents consumed over 6908 kJ in one meal, which was about 62% of their estimated daily energy requirements (Ebbeling et al., 2004). It seems likely that both the large portions and the high energy density of the foods in fast food outlets contribute to excessive energy intakes, but it is important to determine whether these two influences on intake interact or simply add together. Several recent studies have investigated how the combined effects of energy density and portion size influence energy intake. In a controlled laboratory study, Kral et al. (2004) served a main lunch entrée at two energy density levels (5.23 kJ/g and 7.32 kJ/g), in three different portion sizes (500 g, 700 g, 900 g) on different days. Subjects consumed 925 kJ more (56%) when served the largest portion of the high-energy-dense entrée, compared to when served the smallest portion of the low-energy-dense entrée. Interestingly, there was no interaction between the effects of energy density and portion size, indicating that both factors acted independently to affect energy intake. When increased simultaneously, the effects of energy density and portion size added together to increase energy intake (Fig. 8.4).
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Fig. 8.4 Energy intakes (mean ± SEM) for women (n = 39) by energy density and portion size. The effects of portion size and energy density add together to influence energy intake. Reproduced with permission by the American Journal of Clinical Nutrition © Am J Clin Nutr. American Society for Clinical Nutrition (Kral et al., 2004).
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Another study in which the additive effects of energy density and portion size were examined over two days showed that the effects persisted beyond a single meal and that larger portions of higher-energy-dense foods had the greatest impact on energy intake (Rolls et al., 2004c). Thus, both in the short term and over 2 days, the effects of portion size and energy density added together to influence ad libitum intake. In some situations, however, consumption of large portions can decrease overall energy intake if the food has a low energy density. A recent controlled study showed that consumption of a large portion of a food low in energy density at the start of a meal can decrease energy intake at the rest of the meal (Rolls et al., 2004d). On different days, subjects were required to consume a first course salad, which was varied in portion size (150 and 300 g) and energy density (1.38, 2.80, and 5.56 kJ/g); the first course was followed by a main course of pasta that was consumed ad libitum. Compared to having no first course, consuming the low-energy-dense salads reduced meal energy intake (by 7% for the small portion and 12% for the large), and consuming the high-energy-dense salads increased intake (by 8% for the small portion and 17% for the large). When two salads with the same number of calories were compared, meal intake was decreased more when the larger portion of the lower-energy-dense salad was consumed (Fig. 8.5). It has also been shown that consuming a low-energy-dense soup at the start of a meal reduced overall meal intake (Rolls et al., 1999b).
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Fig. 8.5 Energy intakes (mean ± SEM) for women (n = 42) after consumption of compulsory first course salads differing in portion size (g) and energy density (kJ/g). Difference in meal intake compared to consuming no salad: * P < 0.05; *** P < 0.0001. Intake was influenced by both energy density and the portion of salad. Reprinted with permission from the American Dietetic Association (Rolls et al., 2004d).
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These studies indicate that energy density and portion size work together to influence energy intake and satiety and suggest several different strategies that can help to lower energy intake and increase satiety (Ello-Martin et al., 2005). When choosing entrées to be consumed ad libitum, reductions in both energy density and portion size can significantly decrease energy intake while maintaining fullness. In contrast, when choosing a first course, the greatest enhancement of satiety and reduction in overall meal intake was seen with large portions of foods low in energy density such as salad or soup. Understanding how energy density and portion size work together can lead to more effective nutrition education messages than simply to ‘eat less’. Instead, messages may be focused on encouraging the consumption of satisfying portions of foods with a low energy density. Strategies to lower the energy density of meals involve reducing fat and adding water-rich foods, such as soups, vegetables and fruits (Rolls, 2005; Rolls and Barnett, 2003; Rolls et al., 2004a).
8.4.1 Are large portions making us obese? There are few studies on the relationship between food portion size and weight status, and even fewer studies that also address dietary energy density. Nationally representative data for children indicate that portion size alone accounted for 17 to 19% of the variance in energy intake (McConahy et al., 2004); in other words, larger portions were associated with higher intakes. In addition, children with a higher BMI consumed portions of foods that were as much as 100% larger than those consumed by children with a lower BMI (McConahy et al., 2002). These analyses, however, did not also examine the energy density of the foods consumed. This last point is important because large portions of low-energy-dense foods would likely be associated with a lower weight status. A small study in the Netherlands that examined both portion size and energy density indicated that obese women consume larger portions of high-energy-dense foods and smaller portions of low-energy-dense foods, as compared to non-obese women (Westerterp-Plantenga et al., 1996). While calculating dietary energy values in large groups of free-living individuals can be a complex task (Ledikwe et al., 2005), there is a need for nationally representative epidemiological studies examining relationships between food portion size and weight status that take energy density into account. Even though the trend toward larger portion sizes coincided with an increase in the prevalence of obesity, this does not prove a causal link. Similarly, data indicating that large portion sizes increase energy intake do not show a definitive relationship between portion size and weight status; nevertheless, the available data do support the hypothesis that portion size could play a role in the obesity epidemic.
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8.5 Strategies to moderate the influence of portion size on energy intake A number of recent reports have included statements regarding food portion sizes (US Department of Health and Human Services, 2001; World Health Organization, 2003). The Food and Drug Administration (FDA) Report, entitled ‘Calories Count’ (2004), recommended that foods be labeled as a single-serving if they could be reasonably consumed at one sitting because part of the problem people have identifying appropriate food portions may arise from difficulties in interpreting the information on food labels (Seligson, 2003). The report also encouraged food manufactures to use appropriate comparative labeling statements and urged the restaurant industry to provide point of purchase information. The 2005 Dietary Guidelines Advisory Committee acknowledged the importance of energy density in making food choices (Dietary Guidelines Advisory Committee, 2005), and suggested that limiting portion sizes, especially of energy-dense foods, could help to reduce calorie intake. On the other hand, consumption of low-energy dense foods that are nutrient-dense ‘provides individuals a way to meet nutrient needs while avoiding the overconsumption of calories’ (US Department of Health and Human Services and US Department of Agriculture, 2005). Research is needed to determine if adding information about energy density to food packages could be a useful tool for helping consumers to choose appropriate portions and to rapidly compare the energy content of similar foods. One approach to limiting the intake of energy-dense foods is to impose penalties, such as ‘sin taxes’ on beverages and foods high in fat and energy (Horgen and Brownell, 2002). However, determining which items should be taxed is problematic and it is not clear whether foods with large portion sizes should also be taxed. In addition, there are no data on whether such taxes would significantly impact food choices. An alternative approach would be through incentives to provide healthful, low-energy-dense foods and to provide reasonable portions. The FDA considered pilot testing the use of their name and logo on menus and advertisements as an incentive for restaurants to provide patrons with voluntary point-of-purchase nutrition information (Food and Drug Administration’s Obesity Working Group, 2004). This would allow patrons to make informed decisions. It would also provide the food industry with motivation to provide a greater range of portion sizes and to make smaller portions more appealing. While it is not feasible for restaurants to serve portions based on an individual customer’s energy needs, the restaurant industry can provide a variety of choices that would make it easier for customers to eat less. More attractive pricing strategies (French, 2003; Horgen and Brownell, 2002) could be used to promote the selection of smaller portion sizes. However, smaller portions or ‘eating less’ may not always be an effective solution since it is not just large portion sizes that increase energy
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intake, but rather, large portions of energy-dense foods. Instead, foods could be modified to give consumers satisfying portions and good taste as well as less energy at a reasonable price. One strategy is to decrease the energy density of menu items. Reductions in energy density are unlikely to affect customer satisfaction if palatability is not compromised and cost is not increased. A combination of fat reduction along with the addition of waterrich vegetables could reduce the energy density of popular foods such as burgers, sandwiches and pizza. It is likely that, with unit foods such as these, patrons will order and consume their usual portion size, but will ingest less energy while feeling just as full and satisfied (Rolls et al., 2004e). In one study, a fish dish was substantially reduced in fat and energy, with no effect on how much people liked the dish, how well it matched their expectations, and how likely they would be to purchase it again (Stubenitsky et al., 2000). Even small reductions in energy density are likely to have a big impact at a population level. For example, using an alternative method for cooking French fries in fast food restaurants, which decreases fat absorption, could lead to a significant reduction in per capita energy consumption (MorleyJohn et al., 2002). There is a need for extensive funding to deliver effective educational messages that not only emphasize limiting intake of foods with a high energy density, but also encourage consuming foods with a low energy density, such as fruits and vegetables. Organizations that have been successful at increasing consumption of foods low in energy density, such as the Produce for Better Health Foundation (Foerster et al., 1995), should be rewarded with larger budgets. Policy makers need to organize a well-funded campaign using marketing and psychological techniques, as sophisticated as those being used by industry, to help consumers understand the long-term health effects of eating large portions of energy-dense foods (Tillotson, 2002). This can help consumers equip themselves with the knowledge and skills to adequately determine portions that are appropriate to their energy requirements. When faced with large portions of energy-dense, palatable foods in restaurants, people should adopt strategies to limit their intake, such as ordering reduced-sized portions, saving part of the entrée for another meal, or sharing with a friend. Consumers also need to encourage the food industry to provide high quality, low-energy-dense foods. It is important that consumers purchase these items when available so that the food industry has an economic incentive to provide tasty, healthful options that can be consumed in reasonable portions without promoting excessive energy intake.
8.6 The future: the eating environment and obesity There is increasing evidence that excessive food portions, particularly of energy-dense foods, contribute to the overconsumption of energy. Telling
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people to simply ‘eat less’ is not likely to be an effective solution, since it is not just large portion sizes that increase energy intake, but rather, large portions of energy-dense foods. Large portions of foods low in energy density such as vegetables, fruits and broth-based soups can aid weight management by providing satisfying portions with few calories (Rolls, 2005; Rolls and Barnett, 2003). There is a need to deliver effective educational messages that combine the principles of portion size and energy density. The development and intensive marketing of appealing, low-energy-dense foods can help create an environment in which consumers are better able to maintain a healthy weight. Successful strategies will not only require cooperation among the food and restaurant industries, policy makers, and scientists, but will also require consumers to understand and accept the importance of eating reasonable food portions for better health.
8.7 References 2005 dietary guidelines advisory committee (2005), ‘Report of the Dietary Guidelines Advisory Committee on the Dietary Guidelines for Americans, 2005’, http://www.health.gov/dietaryguidelines/dga2005/report/, accessed August 19, 2004. american institute for cancer research (2003), ‘Awareness and action: AICR surveys on portion size, nutrition and cancer risk’, http://www.aicr.org/press/ awarenessandaction_03conf.pdf, (accessed 17 September 2004). barkeling, b., elkman, s. and rossner, s. (1992), ‘Eating behaviour in obese and normal weight 11-year-old children’, Int. J. Obes. Relat. Metab. Disord., 16, 355– 60. bell, e. a., castellanos, v. h., pelkman, c. l., thorwart, m. l. and rolls, b. j. (1998), ‘Energy density of foods affects energy intake in normal-weight women’, Am. J. Clin. Nutr., 67, 412–20. binkley, j. k., eales, j. and jekanowski, m. (2000), ‘The relation between dietary change and rising US obesity’, Int. J. Obes., 24, 1032–9. birch, l. l. and fisher, j. o. (1998), ‘Development of eating behaviors among children and adolescents’, Pediatrics, 101, 539–49. birch, l. l., mcphee, l., shoba, b. c., steinberg, l. and krehbiel, r. (1987), ‘Clean up your plate: effects of child feeding practices on the conditioning of meal size’, Learn. Motiv., 18, 301–17. bowman, s. a., gortmaker, s. l., ebbeling, c. b., pereira, m. a. and ludwig, d. s. (2004), ‘Effects of fast-food consumption on energy intake and diet quality among children in a national household study’, Pediatrics, 113, 112–18. cho, s., dietrich, m., brown, c. j., clark, c. a. and block, g. (2003), ‘The effect of breakfast type on total daily energy intake and body mass index: results from the third National Health and Nutrition Examination Survey (NHANES III)’, J. Am. Coll. Nutr., 22, 296–302. clemens, l. h. e., slawson, d. l. and klesges, r. c. (1999), ‘The effect of eating out on quality of diet in premenopausal women’, J. Am. Diet. Assoc., 99, 442–4. diliberti, n., bordi, p., conklin, m. t., roe, l. s. and rolls, b. j. (2004), ‘Increased portion size leads to increased energy intake in a restaurant meal’, Obes. Res., 12, 562–8. drewnowski, a. and specter, s. e. (2004), ‘Poverty and obesity: the role of energy density and energy costs’, Am. J. Clin. Nutr., 79, 6–16.
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ebbeling, c. b., sinclair, k. b., pereira, m. a., garcia-lago, e., feldman, h. a. and ludwig, d. s. (2004), ‘Compensation for energy intake from fast food among overweight and lean adolescents’, JAMA, 291, 2828–33. ello-martin, j. a., ledikwe, j. h. and rolls, b. j. (2005),‘The influence of food portion size and energy density on energy intake: implications for weight management’, Am. J. Clin. Nutr., (in press). fisher, j. o., rolls, b. j. and birch, l. l. (2003), ‘Children’s bite size and intake of an entrée are greater with large portions than with age-appropriate or self-selected portions’, Am. J. Clin. Nutr., 77, 1164–70. foerster, s. b., kizer, k. w., disogra, l. k., bal, d. g., krieg, b. f. and bunch, k. l. (1995), ‘California’s “5 a day – for better health!” campaign: an innovative population-based effort to effect large-scale dietary change’, Am. J. Prev. Med., 11, 124–31. food and drug administration’s obesity working group (2004), US Food and Drug Administration. Center for Food Safety and Applied Nutrition. french, s. a. (2003), ‘Pricing effects on food choices’, J. Nutr., 133, 841S–3S. french, s. a., harnack, l. and jeffery, r. w. (2000), ‘Fast food restaurant use among women in the Pound of Prevention study: dietary, behavioral and demographic correlates’, Int. J. Obes., 24, 1353–9. french, s. a., story, m., neumark-sztainer, d., fulkerson, j. a. and hannan, p. (2001), ‘Fast food restaurant use among adolescents: associations with nutrient intake, food choices and behavioral and psychosocial variables’, Int. J. Obes., 25, 1823– 33. harnack, l. j., jeffery, r. w. and boutelle, k. n. (2000), ‘Temporal trends in energy intake in the United States: an ecologic perspective’, Am. J. Clin. Nutr., 71, 1478–84. horgen, k. b. and brownell, k. d. (2002), ‘Comparison of price change and health message interventions in promoting healthy food choices’, Health Psychol., 21, 505–12. kant, a. k. and graubard, b. i. (2004), ‘Eating out in America, 1987–2000: trends and nutritional correlates’, Prev. Med., 38, 243–9. kral, t. v. e., roe, l. s. and rolls, b. j. (2004), ‘Combined effects of energy density and portion size on energy intake in women’, Am. J. Clin. Nutr., 79, 962–8. ledikwe, j. h., blanck, h. m., kettel-khan, l. et al. (2005), ‘Dietary energy density determined by eight calculation methods in a nationally representative United States population’, J. Nutr., 135, 273–8. lin, b.-h., guthrie, j. and frazao, e. (1999), ‘Nutrient contribution of food away from home’, in Frazao, E, America’s Eating Habits: Changes and Consequences, US Department of Agriculture/Economic Research Service, 213–42. matthiessen, j. fagt, s., biltoft-jensen, a., beck, a. m. and ovesen, l. (2003), ‘Size makes a difference’, Public Health Nutr., 6, 65–72. mcconahy, k. l., smiciklas-wright, h., birch, l. l., mitchell, d. c. and picciano, m. f. (2002), ‘Food portions are postively related to energy intake and body weight in early childhood’, J. Pediatr., 140, 340–7. mcconahy, k. l., smiciklas-wright, h., mitchell, d. c. and picciano, m. f. (2004), ‘Portion size of common foods predicts energy intake among preschool-aged children’, J. Am. Diet. Assoc., 104, 975–9. mccrory, m. a., fuss, p. j., hays, n. p., vinken, a. g., greenberg, a. s. and roberts, s. b. (1999), ‘Overeating in America: association between restaurant food consumption and body fatness in healthy adult men and women ages 19–80’, Obes. Res., 7, 564–71. morley-john, j., swinburn, b. a., metcalf, p. a. and raza, f. (2002), ‘Fat content of chips, quality of frying fat and deep-frying practices in New Zealand fast food outlets’, Aust. NZ J. Public Health, 26, 101–6.
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national alliance for nutrition and activity (NANA) (2002), ‘From wallet to waistline: the hidden costs of super sizing’. http://www.cspinet.org/w2w.pdf, accessed July 2, 2002. nestle, m. (2003), ‘Increasing portion sizes of American diets: more calories, more obesity’, J. Am. Diet. Assoc., 103, 39–40. nielsen, s. j. and popkin, b. m. (2003), ‘Patterns and trends in food portion sizes, 1977–1998’, J. Am. Med. Assoc., 289, 450–3. paeratakul, s., ferdinand, d. p., champagne, c. m., ryan, d. h. and bray, g. a. (2003), ‘Fast-food consumption among US adults and children: dietary and nutrient intake profile’, J. Am. Diet. Assoc., 103, 1332–8. prentice, a. m. and jebb, s. a. (2003), ‘Fast foods, energy density and obesity: a possible mechanistic link’, Obes. Rev., 4, 187–94. rolls, b. (2005), The Volumetrics Eating Plan, New York, HarperCollins Publishers, Inc. rolls, b. and barnett, r. a. (2003), The Volumetrics Weight-Control Plan: Feel Full on Fewer Calories, New York, HarperTorch. rolls, b. j., bell, e. a., castellanos, v. h., chow, m., pelkman, c. l. and thorwart, m. l. (1999a), ‘Energy density but not fat content of foods affected energy intake in lean and obese women’, Am. J. Clin. Nutr., 69, 863–71. rolls, b. j., bell, e. a. and thorwart, m. l. (1999b), ‘Water incorporated into a food but not served with a food decreases energy intake in lean women’, Am. J. Clin. Nutr., 70, 448–55. rolls, b. j., engell, d. and birch, l. l. (2000), ‘Serving portion size influences 5-yearold but not 3-year old children’s food intakes’, J. Am. Diet. Assoc., 100, 232–4. rolls, b. j., morris, e. l. and roe, l. s. (2002), ‘Portion size of food affects energy intake in normal-weight and overweight men and women’, Am. J. Clin. Nutr., 76, 1207–13. rolls, b. j., ello-martin, j. a. and tohill, b. c. (2004a),‘What can intervention studies tell us about the relationship between fruit and vegetable consumption and weight management?’ Nutr. Rev., 62, 1–17. rolls, b. j., roe, l. s., kral, t. v. e., meengs, j. s. and wall, d. e. (2004b), ‘Increasing the portion size of a packaged snack increases energy intake in men and women’, Appetite, 42, 63–9. rolls, b. j., roe, l. s. and meengs, j. s. (2004c), ‘Reducing the energy density and portion size of foods decreases energy intake over two days’, Obes. Res., 12, A5. rolls, b. j., roe, l. s. and meengs, j. s. (2004d), ‘Salad and satiety: energy density and portion size of a first course salad affect energy intake at lunch’, J. Am. Diet. Assoc., 104, 1570–6. rolls, b. j., roe, l. s., meengs, j. s. and wall, d. e. (2004e), ‘Increasing the portion size of a sandwich increases energy intake’, J. Am. Diet. Assoc., 104, 367–72. rolls, b. j., roe, l. s. and meengs, j. s. (in press), ‘The effect of increased portion size on energy intake is sustained over two days’. J. Am. Diet. Assoc. rozin, p., kabnick, k., pete, e., fischler, c. and shields, c. (2003), ‘The ecology of eating: smaller portion sizes in France than in the United States help explain the French paradox’, Psychol. Sci., 14, 450–4. seligson, f. h. (2003), ‘Serving size standards: can they be harmonized?’ Nutr. Today, 38, 247–53. siegel, p. s. (1957), ‘The completion compulsion in human eating’, Psychol. Rep., 3, 15–16. slawson, d. l. and eck, l. h. (1997), ‘Intense practice enhances accuracy of portion size estimation of amorphous foods’, J. Am. Diet. Assoc., 97, 295–7. smiciklas-wright, h., mitchell, d. c., mickle, s. j., goldman, j. d. and cook, a. (2003), ‘Foods commonly eaten in the United States, 1989–1991 and 1994–1996: are the portion sizes changing?’ J. Am. Diet. Assoc., 103, 41–7.
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stubenitsky, k., aaron, j. i., catt, s. l. and mela, d. j. (2000), ‘The influence of recipe modification and nutritional information on restaurant food acceptance and macronutrient intakes’, Public Health Nutr., 3, 201–9. tillotson, j. e. (2002),‘We’re fat and getting fatter! What is the food industry’s role?’ Nutr. Today, 37, 136–8. us department of health and human services (2001), The Surgeon General’s Call to Action to Prevent and Decrease Overweight and Obesity, Rockville, MD, US Department of Health and Human Services, Public Health Service, Office of the Surgeon General. us department of health and human services and us department of agriculture (2005), Dietary Guidelines for Americans 2005, Washington, DC. wansink, b. (1996), ‘Can package size accelerate usage volume?’ J. Marketing, 60, 1–14. wansink, b. and park, s. b. (2001), ‘At the movies: how external cues and perceived taste impact consumption volume’, Food Qual. Prefer., 12, 69–74. westerterp-plantenga, m. s., pasman, w. j., yedema, m. j. w. and wijckmansduijsens, n. e. g. (1996), ‘Energy intake adaptation of food intake to extreme energy densities of food by obese and non-obese women’, Eur. J. Clin. Nutr., 50, 401–7. world health organization (2003), World Health Organization (WHO Technical Report Series, No. 916). Geneva, Switzerland. world health organization (2004), ‘Obesity and overweight’, http://www. who.int/dietphysicalactivity/publications/facts/obesity/en/, (accessed 4 October 2004). young, l. r. and nestle, m. (2002), ‘The contribution of expanding portion sizes to the US obesity epidemic’, Am. J. Public Health, 92, 246–9. young, l. r. and nestle, m. (2003), ‘Expanding portion sizes in the US marketplace: implications for nutrition counseling’, J. Am. Diet. Assoc., 103, 231–4.
8.1 Introduction: the growth in portion sizes Obesity is a rapidly growing, world-wide public health problem. In recent decades, there has been a significant increase in the prevalence of obesity. The World Health Organization estimates that globally there are over 1 billion adults and 17 million children who are overweight or obese (World Health Organization, 2004). It is unlikely that our biology could have changed in several decades, so other explanations for this surge in obesity rates must be found. One possible reason for the increase is that the environment in Westernized societies has altered, so that overconsumption of energy has become easier. At the same time, opportunities for physical activity have declined. Thus, it is increasingly difficult for individuals to match energy intake to energy output in order to maintain a healthy body weight. Some of the changes in the eating environment that encourage overeating are the increasing availability of inexpensive high-energy-dense (kJ/g) foods, the wide variety of palatable foods, the increasing frequency of meals consumed outside of the home, and the rise in portion sizes. While all of these changes may stimulate excess intake, we will present data suggesting that large portion sizes, particularly of energy-dense foods, are contributing to the epidemic of obesity, and we will present constructive measures that could help to improve the eating environment.
1
Supported by NIH grants R37DK039177 and R01DK059853.
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8.1.1 Increasing portion sizes Studies of food portions offered at fast food outlets, chain restaurants, and convenience stores indicate that portion sizes of many items have increased (Young and Nestle, 2002). According to Nestle (2003), this trend began in the USA as early as the 1970s, with portion sizes increasing sharply in the 1980s and continuing to rise. Data from Denmark show similar trends (Matthiessen et al., 2003).The growth of portion sizes has been most evident in fast food restaurants where the ‘supersizing’ of some menu items is relatively common (Harnack et al., 2000). Items available at fast food restaurants are estimated to be two to five times larger than two decades ago (Young and Nestle, 2003). In general, food packaging and common portion sizes of popular dishes are 25% larger in the USA than in France where rates of obesity are lower (Rozin et al., 2003). With the availability of many foods in larger sizes, it is not surprising that epidemiological studies indicate people are consuming larger portions of food (Smiciklas-Wright et al., 2003).
8.2 Studies showing that portion size affects energy intake 8.2.1 Adults Although the increase in the size of portions and the prevalence of overweight and obesity have occurred in parallel, a crucial step in assessing a causal relationship between portion size and obesity is to determine experimentally whether portion size affects energy intake. Recent controlled studies clearly show that portion size does affect energy intake. When we tested how adults responded to four different portions of macaroni and cheese served on different days, we found that the bigger the portion, the more participants ate (Rolls et al., 2002). They consumed 30% more energy (676 kJ) when offered the largest portion (1000 g) compared to the smallest portion (500 g). The effect was seen both when the portion on the plate was determined by the investigator and when the participants served themselves from bowls containing different size portions. Of particular interest was the finding that, despite the difference in intake, participants reported similar ratings of hunger and fullness after eating. The results were not affected by subject characteristics including sex, body mass index, or concern about food intake or body weight. After the study was over, less than half (45%) of the subjects reported noticing that there were differences in the portions served. It is surprising that, in a controlled laboratory setting where the main focus was food and eating, many participants in the study appeared to be unaware of the changes in the amount of food offered and the subsequent effect on their intake, hunger, and satiety. It seems likely that, when individuals are in situations where there are more distractions, such as when eating out, they would be even less aware of portion size.
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It could be argued that the effects of portion size on intake are specific to foods like macaroni and cheese that are amorphous or have no defined shape. The portion size of such foods has been shown to be particularly difficult to judge, especially when the portions are large (Slawson and Eck, 1997). We conducted further studies to test whether intake can also be influenced by the portion size of other types of foods, such as those with clearly defined shapes or units. People tend to eat in units. That is, if they are offered a food that comes in a preportioned unit, such as a cookie, most people will eat the whole cookie (Siegel, 1957). One of the most common unit foods is the sandwich. In most fast food establishments there is a choice of sandwich sizes; often the larger sandwiches are purchased because the consumers perceive them as better value in that they get more food for their money (National Alliance for Nutrition and Activity, NANA, 2002). A key question is, if consumers choose a larger sandwich, are they likely to eat more? To test this, on four different days, we offered men and women submarine sandwiches that varied in size: 6, 8, 10, and 12 inches (15, 20, 25, 30 cm) (Rolls et al., 2004e). We found a systematic and significant effect of portion size on intake for both men and women (Fig. 8.1). When served the 12-inch sandwich compared to the 6-inch sandwich, women consumed 31% more energy (665 kJ) and men consumed 56% more energy (1485 kJ). Ratings of hunger and fullness after lunch did not differ significantly when subjects were served the 8-, 10-, and 12-inch (20-, 25-, 30-cm) sandwiches, despite the increase in energy intake. It appears that, when served bigger portions, consumers override or adjust their level of satiety to accommodate greater energy intakes.
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The amount of food in a package or container may also influence how much is eaten. Some prepackaged foods come in a wide variety of sizes; for example, bags of potato chips range from 28 g single-serving bags to 560 g family-size bags. To test how the size of the bag affects intake, on five occasions we served men and women an afternoon snack that consisted of 28, 42, 85, 128 or 170 g of potato chips in a plain, unlabelled foil bag (Rolls et al., 2004b). Participants ate directly from the bag so that they had few visual cues to guide consumption. The results showed that portion size had a significant effect on snack intake for both the men and the women (Fig. 8.2). For example, when served the 170 g package, women ate 18% (200 kJ) more and men ate 37% (511 kJ) more than when served the 85 g package. As subjects increased their snack intake with increasing package size, they also reported feeling fuller; however, they did not adjust their intake at the subsequent dinner meal to compensate for the increased energy intake and fullness. Thus, bigger portions of a prepackaged snack increased energy intake in the short term. It is not clear that all prepackaged foods will have a similar effect. It is possible that the effect will be greatest for highly palatable foods, such as chips, that people find difficult to stop eating. Additional studies conducted in a variety of situations confirm that the package or container size of a variety of foods can affect how much food
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Fig. 8.2 At a mid-afternoon snack on different days, men (n = 26) and women (n = 34) were offered one of five package sizes containing different portions of potato chips (crisps). Both men and women increased their intake of chips as the package size increased; furthermore, subjects did not significantly adjust their intake at dinner for the excess energy consumed with the snack. Means within each sex with different letter are significantly different (P < 0.02).
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is prepared and eaten (Wansink, 1996). When women were given a 2 lb box of spaghetti and asked to take out enough to make a dinner for two, they removed an average of 302 strands. But when given a 1 lb box, they removed only 234 strands. When frying chicken, women poured 4.3 ounces (126 ml) of cooking oil from a 32-oz bottle, but only 3.5 ounces (103 ml) from a 16oz bottle. When people were asked how many chocolate candies they would eat while watching a movie by themselves, participants poured 63 from a small package that contained 114 candies, 103 from a package double in size, and 122 from a package triple in size. That is, they poured about twice as much from a jumbo bag, a difference of about 1046 kJ (Wansink, 1996). In a cinema, consumers were given either a medium (120 g) or large (240 g) bucket of popcorn. Subjects rated the taste of the popcorn, and were divided into two groups depending upon whether they perceived the taste as favorable or unfavorable. The results showed an effect of the portion size of popcorn on intake regardless of how the taste of popcorn was rated (Wansink and Park, 2001). Thus, it is not just the palatability of foods that is driving intake up when large portions are available. A number of controlled studies show that both in the laboratory and in more naturalistic settings, the portion size and package size of a variety of foods can affect energy intake in adults in the short term. It is possible that, after a bout of overeating stimulated by large portions, compensatory mechanisms will limit subsequent intake. We tested this in a study in which the portion size was increased for all foods served to men and women over a 2-day period (Rolls et al., in press). The results showed a significant effect of portion size on energy intake over the 2 days. When the portions of all foods were doubled, energy intake on both days increased for all subjects by a mean of 26% (2218 kJ/d for women and 3402 kJ/d for men) (Fig. 8.3). Although subjects reported feeling more full after they consumed the larger portions, they did not compensate for the excess energy eaten over the course of the first day by reducing their intake on the second day. Thus, these results show that the effects of portion size can persist over several days and are associated with significant increases in daily intakes. Studies of longer term effects of portion size on energy intake are in progress.
8.2.2 Children While it has been clearly shown that adults respond to increasing portions by eating more, they probably did not start life responding in this way. A recent analysis of food survey data over a 20-year period indicates that, despite changes in the eating environment, there has been remarkable stability in the average portion size of foods consumed by children in the second year of life (McConahy et al., 2002). A controlled laboratory study that we conducted confirms that, in young children, intake is relatively unaffected by environmental cues such as portion size. When we fed 3-year-olds three different portions of macaroni and cheese at three separate lunches,
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they ate the same amount at each meal. Their intake was therefore unaffected by portion size. In contrast, 5-year-old children responded as adults do, in that they ate significantly more as the portions increased. This response to portion size occurred even though their hunger did not differ at the start of the meals (Rolls et al., 2000). Similarly, Fisher and colleagues (2003) found that 4-year-old children ate 25% more when they were served an entrée that was twice the size of an age-appropriate portion. In this study, the children who increased their intake the most when served large portions were those who had been identified as more likely to eat in the absence of hunger. It is not clear why children are more influenced by portion size as they age. Data suggest that early experiences lead to the development of behaviors that shape eating habits. In one study, 4-year-old children who were rewarded for cleaning their plates increased their energy intake. On the other hand, children who were taught to focus on satiety cues, indicated by the fullness in their stomachs, ate an appropriate amount of food (Birch et al., 1987).Thus, the response to portion size by children could be a learned behavior which leads to a shift of attention away from internal hunger and satiety cues toward food cues in the external environment. A lack of response to satiety signals may predispose children to overeat in an environment in which large portions of palatable foods are readily available (Barkeling et al., 1992; Birch and Fisher, 1998).The influence of large portions on intake, however, has been shown to be moderated simply by allowing children to serve themselves. One study demonstrated that children ate 25% less of a large entrée when they decided for themselves how much
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food to put on their plates, compared to when they were served the large portion of the entrée by an adult (Fisher et al., 2003).
8.3 Eating out and portion size Although there is some evidence that portions consumed at home are increasing (Nielsen and Popkin, 2003; Young and Nestle, 2002), the large portions served in restaurants may be a bigger problem for weight management. The increase in the prevalence of obesity since the 1970s coincides with an increase in the number of meals eaten outside the home (Harnack et al., 2000; Lin et al., 1999). Today, Americans are 40% more likely to consume meals from restaurants three or more times a week as they were in the late 1980s (Kant and Graubard, 2004). A number of studies indicate that meals consumed away from home have a lower diet quality and are higher in energy than at-home foods (Bowman et al., 2004; Clemens et al., 1999; French et al., 2001; Kant and Graubard, 2004; Paeratakul et al., 2003). Furthermore, in both adolescents and adults, the frequency of eating out is associated with an increase in energy and fat intake (Clemens et al., 1999; French et al., 2001; Kant and Graubard, 2004). For example, women who eat out frequently (more than six times a week) have been shown to have daily energy intakes approximately 1200 kJ higher than those who eat at restaurants less often (Clemens et al., 1999). In addition to high energy intakes, data show a relationship between eating out and weight status (Binkley et al., 2000; Cho et al., 2003; French et al., 2000; Kant and Graubard, 2004; McCrory et al., 1999). Nationally representative data indicate that the proportion of food consumed from fastfood restaurants is positively associated with body mass index (BMI) in both men and women (Binkley et al., 2000). One prospective study found that, over 3 years, an increase in the frequency of fast food consumption was associated with an increase in body weight (French et al., 2000). The high availability of large portions of energy-dense foods in restaurants may provide an explanation for the association between eating out and increased body weight. A cross-cultural analysis revealed that the portion sizes of popular restaurant dishes were 25% larger in the USA than in France, a country with substantially lower rates of obesity (Rozin et al., 2003). Restaurants have found that customers appreciate good value, and this translates into large portions at a low price. Since food is only a small percentage of the cost of a restaurant meal, giving customers more food is an excellent economic strategy if it increases total sales. This is possible because agricultural subsidies have helped to reduce the cost of some foods and commodities, such as vegetable oil and sugar, which have become very inexpensive (Drewnowski and Specter, 2004; Nestle, 2003). Thus the practice of ‘supersizing’ (giving customers a lot more food and energy for
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only a small additional cost) is widespread, particularly in fast food establishments. Restaurants may be giving consumers what they want in terms of value, but a crucial issue is whether people can adjust their energy intake to their energy needs when tempted with large portions of energy-dense, palatable foods. The American Institute of Cancer Research has provided data that offer insight into how individuals view portion size when dining out (American Institute for Cancer Research, 2003). In a survey of more than 1000 adults, 69% indicated that, when dining out, they finish their entrées all or most of the time. Of those adults, 30% reported that they would have been satisfied with a smaller portion. This suggests that, when eating out, many adults ignore satiety signals and eat beyond the point of noticeable fullness. Additionally, a number of survey respondents (42%) reported that they determine the amount of food to eat according to what they are used to eating. Thus, the portion sizes that individuals customarily eat may be related to frequent exposure to large portions over time. A recent study demonstrates that the portions served in restaurants can directly affect how much is eaten. We tested how increasing the portion size of a popular dish, while keeping the price the same, would affect intake in a restaurant setting (Diliberti et al., 2004). An entrée, baked ziti, was offered ten times over 5 months and 180 adult customers purchased the dish during that period. On different days, the portion was varied between a standard portion (248 g, 1766 kJ) and a large portion (377 g, 2647 kJ). Results showed that portion size had a significant impact on intake, such that mean intake of the standard portion was 1671 kJ and of the larger portion was 2390 kJ. Thus when customers were served 50% more they ate 43% more, equivalent to 719 kJ. A survey filled out by the customers showed no difference in ratings of the appropriateness of the two portions. Thus, in restaurants as well as in the laboratory, portion size has a significant impact on energy intake, and it is likely that the consumers are often unaware of this effect.
8.4 Portion size, energy intake and obesity When eating out, portion size is one of a number of variables that could affect consumption. Having a wide variety of palatable foods, eating in a convivial atmosphere with friends, and the consumption of alcohol may also increase energy intake. The high energy density (kJ/g) of restaurant meals is likely to promote excess intake. A systematic series of studies indicates that individuals consistently consume more energy when presented with foods having a higher energy density than with similar foods having a lower energy density (Bell et al., 1998; Rolls et al., 1999a,b). Prentice and Jebb (2003) recently compiled the energy density values of foods from wellknown fast food outlets in Britain, finding that the energy density of the entire menu (beverages were not included) from these restaurants was
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12.0 kJ/g. Further work is needed to determine the average energy density of fast food meals and to examine the influence of the new, popular salad options on meal energy density at these establishments. For comparative purposes, the energy density of the US diet, based on all foods consumed over two days, was found to be 7.8 kJ/g (Ledikwe et al., 2005). The relatively high energy density of fast food can facilitate the overconsumption of energy. For example, when served a fast food meal with extra large portions in a food court, adolescents consumed over 6908 kJ in one meal, which was about 62% of their estimated daily energy requirements (Ebbeling et al., 2004). It seems likely that both the large portions and the high energy density of the foods in fast food outlets contribute to excessive energy intakes, but it is important to determine whether these two influences on intake interact or simply add together. Several recent studies have investigated how the combined effects of energy density and portion size influence energy intake. In a controlled laboratory study, Kral et al. (2004) served a main lunch entrée at two energy density levels (5.23 kJ/g and 7.32 kJ/g), in three different portion sizes (500 g, 700 g, 900 g) on different days. Subjects consumed 925 kJ more (56%) when served the largest portion of the high-energy-dense entrée, compared to when served the smallest portion of the low-energy-dense entrée. Interestingly, there was no interaction between the effects of energy density and portion size, indicating that both factors acted independently to affect energy intake. When increased simultaneously, the effects of energy density and portion size added together to increase energy intake (Fig. 8.4).
925 kJ (P < 0.0001) (Planned comparison)
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2000 Energy intake (kJ)
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0 5.20
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Fig. 8.4 Energy intakes (mean ± SEM) for women (n = 39) by energy density and portion size. The effects of portion size and energy density add together to influence energy intake. Reproduced with permission by the American Journal of Clinical Nutrition © Am J Clin Nutr. American Society for Clinical Nutrition (Kral et al., 2004).
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Another study in which the additive effects of energy density and portion size were examined over two days showed that the effects persisted beyond a single meal and that larger portions of higher-energy-dense foods had the greatest impact on energy intake (Rolls et al., 2004c). Thus, both in the short term and over 2 days, the effects of portion size and energy density added together to influence ad libitum intake. In some situations, however, consumption of large portions can decrease overall energy intake if the food has a low energy density. A recent controlled study showed that consumption of a large portion of a food low in energy density at the start of a meal can decrease energy intake at the rest of the meal (Rolls et al., 2004d). On different days, subjects were required to consume a first course salad, which was varied in portion size (150 and 300 g) and energy density (1.38, 2.80, and 5.56 kJ/g); the first course was followed by a main course of pasta that was consumed ad libitum. Compared to having no first course, consuming the low-energy-dense salads reduced meal energy intake (by 7% for the small portion and 12% for the large), and consuming the high-energy-dense salads increased intake (by 8% for the small portion and 17% for the large). When two salads with the same number of calories were compared, meal intake was decreased more when the larger portion of the lower-energy-dense salad was consumed (Fig. 8.5). It has also been shown that consuming a low-energy-dense soup at the start of a meal reduced overall meal intake (Rolls et al., 1999b).
5000
+ 17% + 8%
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*** –12% ***
2000 1000 0 No salad
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Fig. 8.5 Energy intakes (mean ± SEM) for women (n = 42) after consumption of compulsory first course salads differing in portion size (g) and energy density (kJ/g). Difference in meal intake compared to consuming no salad: * P < 0.05; *** P < 0.0001. Intake was influenced by both energy density and the portion of salad. Reprinted with permission from the American Dietetic Association (Rolls et al., 2004d).
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These studies indicate that energy density and portion size work together to influence energy intake and satiety and suggest several different strategies that can help to lower energy intake and increase satiety (Ello-Martin et al., 2005). When choosing entrées to be consumed ad libitum, reductions in both energy density and portion size can significantly decrease energy intake while maintaining fullness. In contrast, when choosing a first course, the greatest enhancement of satiety and reduction in overall meal intake was seen with large portions of foods low in energy density such as salad or soup. Understanding how energy density and portion size work together can lead to more effective nutrition education messages than simply to ‘eat less’. Instead, messages may be focused on encouraging the consumption of satisfying portions of foods with a low energy density. Strategies to lower the energy density of meals involve reducing fat and adding water-rich foods, such as soups, vegetables and fruits (Rolls, 2005; Rolls and Barnett, 2003; Rolls et al., 2004a).
8.4.1 Are large portions making us obese? There are few studies on the relationship between food portion size and weight status, and even fewer studies that also address dietary energy density. Nationally representative data for children indicate that portion size alone accounted for 17 to 19% of the variance in energy intake (McConahy et al., 2004); in other words, larger portions were associated with higher intakes. In addition, children with a higher BMI consumed portions of foods that were as much as 100% larger than those consumed by children with a lower BMI (McConahy et al., 2002). These analyses, however, did not also examine the energy density of the foods consumed. This last point is important because large portions of low-energy-dense foods would likely be associated with a lower weight status. A small study in the Netherlands that examined both portion size and energy density indicated that obese women consume larger portions of high-energy-dense foods and smaller portions of low-energy-dense foods, as compared to non-obese women (Westerterp-Plantenga et al., 1996). While calculating dietary energy values in large groups of free-living individuals can be a complex task (Ledikwe et al., 2005), there is a need for nationally representative epidemiological studies examining relationships between food portion size and weight status that take energy density into account. Even though the trend toward larger portion sizes coincided with an increase in the prevalence of obesity, this does not prove a causal link. Similarly, data indicating that large portion sizes increase energy intake do not show a definitive relationship between portion size and weight status; nevertheless, the available data do support the hypothesis that portion size could play a role in the obesity epidemic.
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8.5 Strategies to moderate the influence of portion size on energy intake A number of recent reports have included statements regarding food portion sizes (US Department of Health and Human Services, 2001; World Health Organization, 2003). The Food and Drug Administration (FDA) Report, entitled ‘Calories Count’ (2004), recommended that foods be labeled as a single-serving if they could be reasonably consumed at one sitting because part of the problem people have identifying appropriate food portions may arise from difficulties in interpreting the information on food labels (Seligson, 2003). The report also encouraged food manufactures to use appropriate comparative labeling statements and urged the restaurant industry to provide point of purchase information. The 2005 Dietary Guidelines Advisory Committee acknowledged the importance of energy density in making food choices (Dietary Guidelines Advisory Committee, 2005), and suggested that limiting portion sizes, especially of energy-dense foods, could help to reduce calorie intake. On the other hand, consumption of low-energy dense foods that are nutrient-dense ‘provides individuals a way to meet nutrient needs while avoiding the overconsumption of calories’ (US Department of Health and Human Services and US Department of Agriculture, 2005). Research is needed to determine if adding information about energy density to food packages could be a useful tool for helping consumers to choose appropriate portions and to rapidly compare the energy content of similar foods. One approach to limiting the intake of energy-dense foods is to impose penalties, such as ‘sin taxes’ on beverages and foods high in fat and energy (Horgen and Brownell, 2002). However, determining which items should be taxed is problematic and it is not clear whether foods with large portion sizes should also be taxed. In addition, there are no data on whether such taxes would significantly impact food choices. An alternative approach would be through incentives to provide healthful, low-energy-dense foods and to provide reasonable portions. The FDA considered pilot testing the use of their name and logo on menus and advertisements as an incentive for restaurants to provide patrons with voluntary point-of-purchase nutrition information (Food and Drug Administration’s Obesity Working Group, 2004). This would allow patrons to make informed decisions. It would also provide the food industry with motivation to provide a greater range of portion sizes and to make smaller portions more appealing. While it is not feasible for restaurants to serve portions based on an individual customer’s energy needs, the restaurant industry can provide a variety of choices that would make it easier for customers to eat less. More attractive pricing strategies (French, 2003; Horgen and Brownell, 2002) could be used to promote the selection of smaller portion sizes. However, smaller portions or ‘eating less’ may not always be an effective solution since it is not just large portion sizes that increase energy
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intake, but rather, large portions of energy-dense foods. Instead, foods could be modified to give consumers satisfying portions and good taste as well as less energy at a reasonable price. One strategy is to decrease the energy density of menu items. Reductions in energy density are unlikely to affect customer satisfaction if palatability is not compromised and cost is not increased. A combination of fat reduction along with the addition of waterrich vegetables could reduce the energy density of popular foods such as burgers, sandwiches and pizza. It is likely that, with unit foods such as these, patrons will order and consume their usual portion size, but will ingest less energy while feeling just as full and satisfied (Rolls et al., 2004e). In one study, a fish dish was substantially reduced in fat and energy, with no effect on how much people liked the dish, how well it matched their expectations, and how likely they would be to purchase it again (Stubenitsky et al., 2000). Even small reductions in energy density are likely to have a big impact at a population level. For example, using an alternative method for cooking French fries in fast food restaurants, which decreases fat absorption, could lead to a significant reduction in per capita energy consumption (MorleyJohn et al., 2002). There is a need for extensive funding to deliver effective educational messages that not only emphasize limiting intake of foods with a high energy density, but also encourage consuming foods with a low energy density, such as fruits and vegetables. Organizations that have been successful at increasing consumption of foods low in energy density, such as the Produce for Better Health Foundation (Foerster et al., 1995), should be rewarded with larger budgets. Policy makers need to organize a well-funded campaign using marketing and psychological techniques, as sophisticated as those being used by industry, to help consumers understand the long-term health effects of eating large portions of energy-dense foods (Tillotson, 2002). This can help consumers equip themselves with the knowledge and skills to adequately determine portions that are appropriate to their energy requirements. When faced with large portions of energy-dense, palatable foods in restaurants, people should adopt strategies to limit their intake, such as ordering reduced-sized portions, saving part of the entrée for another meal, or sharing with a friend. Consumers also need to encourage the food industry to provide high quality, low-energy-dense foods. It is important that consumers purchase these items when available so that the food industry has an economic incentive to provide tasty, healthful options that can be consumed in reasonable portions without promoting excessive energy intake.
8.6 The future: the eating environment and obesity There is increasing evidence that excessive food portions, particularly of energy-dense foods, contribute to the overconsumption of energy. Telling
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people to simply ‘eat less’ is not likely to be an effective solution, since it is not just large portion sizes that increase energy intake, but rather, large portions of energy-dense foods. Large portions of foods low in energy density such as vegetables, fruits and broth-based soups can aid weight management by providing satisfying portions with few calories (Rolls, 2005; Rolls and Barnett, 2003). There is a need to deliver effective educational messages that combine the principles of portion size and energy density. The development and intensive marketing of appealing, low-energy-dense foods can help create an environment in which consumers are better able to maintain a healthy weight. Successful strategies will not only require cooperation among the food and restaurant industries, policy makers, and scientists, but will also require consumers to understand and accept the importance of eating reasonable food portions for better health.
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ebbeling, c. b., sinclair, k. b., pereira, m. a., garcia-lago, e., feldman, h. a. and ludwig, d. s. (2004), ‘Compensation for energy intake from fast food among overweight and lean adolescents’, JAMA, 291, 2828–33. ello-martin, j. a., ledikwe, j. h. and rolls, b. j. (2005),‘The influence of food portion size and energy density on energy intake: implications for weight management’, Am. J. Clin. Nutr., (in press). fisher, j. o., rolls, b. j. and birch, l. l. (2003), ‘Children’s bite size and intake of an entrée are greater with large portions than with age-appropriate or self-selected portions’, Am. J. Clin. Nutr., 77, 1164–70. foerster, s. b., kizer, k. w., disogra, l. k., bal, d. g., krieg, b. f. and bunch, k. l. (1995), ‘California’s “5 a day – for better health!” campaign: an innovative population-based effort to effect large-scale dietary change’, Am. J. Prev. Med., 11, 124–31. food and drug administration’s obesity working group (2004), US Food and Drug Administration. Center for Food Safety and Applied Nutrition. french, s. a. (2003), ‘Pricing effects on food choices’, J. Nutr., 133, 841S–3S. french, s. a., harnack, l. and jeffery, r. w. (2000), ‘Fast food restaurant use among women in the Pound of Prevention study: dietary, behavioral and demographic correlates’, Int. J. Obes., 24, 1353–9. french, s. a., story, m., neumark-sztainer, d., fulkerson, j. a. and hannan, p. (2001), ‘Fast food restaurant use among adolescents: associations with nutrient intake, food choices and behavioral and psychosocial variables’, Int. J. Obes., 25, 1823– 33. harnack, l. j., jeffery, r. w. and boutelle, k. n. (2000), ‘Temporal trends in energy intake in the United States: an ecologic perspective’, Am. J. Clin. Nutr., 71, 1478–84. horgen, k. b. and brownell, k. d. (2002), ‘Comparison of price change and health message interventions in promoting healthy food choices’, Health Psychol., 21, 505–12. kant, a. k. and graubard, b. i. (2004), ‘Eating out in America, 1987–2000: trends and nutritional correlates’, Prev. Med., 38, 243–9. kral, t. v. e., roe, l. s. and rolls, b. j. (2004), ‘Combined effects of energy density and portion size on energy intake in women’, Am. J. Clin. Nutr., 79, 962–8. ledikwe, j. h., blanck, h. m., kettel-khan, l. et al. (2005), ‘Dietary energy density determined by eight calculation methods in a nationally representative United States population’, J. Nutr., 135, 273–8. lin, b.-h., guthrie, j. and frazao, e. (1999), ‘Nutrient contribution of food away from home’, in Frazao, E, America’s Eating Habits: Changes and Consequences, US Department of Agriculture/Economic Research Service, 213–42. matthiessen, j. fagt, s., biltoft-jensen, a., beck, a. m. and ovesen, l. (2003), ‘Size makes a difference’, Public Health Nutr., 6, 65–72. mcconahy, k. l., smiciklas-wright, h., birch, l. l., mitchell, d. c. and picciano, m. f. (2002), ‘Food portions are postively related to energy intake and body weight in early childhood’, J. Pediatr., 140, 340–7. mcconahy, k. l., smiciklas-wright, h., mitchell, d. c. and picciano, m. f. (2004), ‘Portion size of common foods predicts energy intake among preschool-aged children’, J. Am. Diet. Assoc., 104, 975–9. mccrory, m. a., fuss, p. j., hays, n. p., vinken, a. g., greenberg, a. s. and roberts, s. b. (1999), ‘Overeating in America: association between restaurant food consumption and body fatness in healthy adult men and women ages 19–80’, Obes. Res., 7, 564–71. morley-john, j., swinburn, b. a., metcalf, p. a. and raza, f. (2002), ‘Fat content of chips, quality of frying fat and deep-frying practices in New Zealand fast food outlets’, Aust. NZ J. Public Health, 26, 101–6.
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national alliance for nutrition and activity (NANA) (2002), ‘From wallet to waistline: the hidden costs of super sizing’. http://www.cspinet.org/w2w.pdf, accessed July 2, 2002. nestle, m. (2003), ‘Increasing portion sizes of American diets: more calories, more obesity’, J. Am. Diet. Assoc., 103, 39–40. nielsen, s. j. and popkin, b. m. (2003), ‘Patterns and trends in food portion sizes, 1977–1998’, J. Am. Med. Assoc., 289, 450–3. paeratakul, s., ferdinand, d. p., champagne, c. m., ryan, d. h. and bray, g. a. (2003), ‘Fast-food consumption among US adults and children: dietary and nutrient intake profile’, J. Am. Diet. Assoc., 103, 1332–8. prentice, a. m. and jebb, s. a. (2003), ‘Fast foods, energy density and obesity: a possible mechanistic link’, Obes. Rev., 4, 187–94. rolls, b. (2005), The Volumetrics Eating Plan, New York, HarperCollins Publishers, Inc. rolls, b. and barnett, r. a. (2003), The Volumetrics Weight-Control Plan: Feel Full on Fewer Calories, New York, HarperTorch. rolls, b. j., bell, e. a., castellanos, v. h., chow, m., pelkman, c. l. and thorwart, m. l. (1999a), ‘Energy density but not fat content of foods affected energy intake in lean and obese women’, Am. J. Clin. Nutr., 69, 863–71. rolls, b. j., bell, e. a. and thorwart, m. l. (1999b), ‘Water incorporated into a food but not served with a food decreases energy intake in lean women’, Am. J. Clin. Nutr., 70, 448–55. rolls, b. j., engell, d. and birch, l. l. (2000), ‘Serving portion size influences 5-yearold but not 3-year old children’s food intakes’, J. Am. Diet. Assoc., 100, 232–4. rolls, b. j., morris, e. l. and roe, l. s. (2002), ‘Portion size of food affects energy intake in normal-weight and overweight men and women’, Am. J. Clin. Nutr., 76, 1207–13. rolls, b. j., ello-martin, j. a. and tohill, b. c. (2004a),‘What can intervention studies tell us about the relationship between fruit and vegetable consumption and weight management?’ Nutr. Rev., 62, 1–17. rolls, b. j., roe, l. s., kral, t. v. e., meengs, j. s. and wall, d. e. (2004b), ‘Increasing the portion size of a packaged snack increases energy intake in men and women’, Appetite, 42, 63–9. rolls, b. j., roe, l. s. and meengs, j. s. (2004c), ‘Reducing the energy density and portion size of foods decreases energy intake over two days’, Obes. Res., 12, A5. rolls, b. j., roe, l. s. and meengs, j. s. (2004d), ‘Salad and satiety: energy density and portion size of a first course salad affect energy intake at lunch’, J. Am. Diet. Assoc., 104, 1570–6. rolls, b. j., roe, l. s., meengs, j. s. and wall, d. e. (2004e), ‘Increasing the portion size of a sandwich increases energy intake’, J. Am. Diet. Assoc., 104, 367–72. rolls, b. j., roe, l. s. and meengs, j. s. (in press), ‘The effect of increased portion size on energy intake is sustained over two days’. J. Am. Diet. Assoc. rozin, p., kabnick, k., pete, e., fischler, c. and shields, c. (2003), ‘The ecology of eating: smaller portion sizes in France than in the United States help explain the French paradox’, Psychol. Sci., 14, 450–4. seligson, f. h. (2003), ‘Serving size standards: can they be harmonized?’ Nutr. Today, 38, 247–53. siegel, p. s. (1957), ‘The completion compulsion in human eating’, Psychol. Rep., 3, 15–16. slawson, d. l. and eck, l. h. (1997), ‘Intense practice enhances accuracy of portion size estimation of amorphous foods’, J. Am. Diet. Assoc., 97, 295–7. smiciklas-wright, h., mitchell, d. c., mickle, s. j., goldman, j. d. and cook, a. (2003), ‘Foods commonly eaten in the United States, 1989–1991 and 1994–1996: are the portion sizes changing?’ J. Am. Diet. Assoc., 103, 41–7.
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stubenitsky, k., aaron, j. i., catt, s. l. and mela, d. j. (2000), ‘The influence of recipe modification and nutritional information on restaurant food acceptance and macronutrient intakes’, Public Health Nutr., 3, 201–9. tillotson, j. e. (2002),‘We’re fat and getting fatter! What is the food industry’s role?’ Nutr. Today, 37, 136–8. us department of health and human services (2001), The Surgeon General’s Call to Action to Prevent and Decrease Overweight and Obesity, Rockville, MD, US Department of Health and Human Services, Public Health Service, Office of the Surgeon General. us department of health and human services and us department of agriculture (2005), Dietary Guidelines for Americans 2005, Washington, DC. wansink, b. (1996), ‘Can package size accelerate usage volume?’ J. Marketing, 60, 1–14. wansink, b. and park, s. b. (2001), ‘At the movies: how external cues and perceived taste impact consumption volume’, Food Qual. Prefer., 12, 69–74. westerterp-plantenga, m. s., pasman, w. j., yedema, m. j. w. and wijckmansduijsens, n. e. g. (1996), ‘Energy intake adaptation of food intake to extreme energy densities of food by obese and non-obese women’, Eur. J. Clin. Nutr., 50, 401–7. world health organization (2003), World Health Organization (WHO Technical Report Series, No. 916). Geneva, Switzerland. world health organization (2004), ‘Obesity and overweight’, http://www. who.int/dietphysicalactivity/publications/facts/obesity/en/, (accessed 4 October 2004). young, l. r. and nestle, m. (2002), ‘The contribution of expanding portion sizes to the US obesity epidemic’, Am. J. Public Health, 92, 246–9. young, l. r. and nestle, m. (2003), ‘Expanding portion sizes in the US marketplace: implications for nutrition counseling’, J. Am. Diet. Assoc., 103, 231–4.