Physical Activity and Nutrition in Children and Youth: An Overview of Obesity Prevention

Preventive Medicine 31, S1–S10 (2000) doi:10.1006/pmed.2000.0686, available online at http://www.idealibrary.com on

INTRODUCTION Physical Activity and Nutrition in Children and Youth: An Overview of Obesity Prevention1 Tom Baranowski, Ph.D.,*,2 James Mendlein, Ph.D.,† Ken Resnicow, Ph.D.,‡ Erica Frank, M.D., M.P.H.,§ Karen Weber Cullen, Dr.P.H., R.D., L.D.,* and Janice Baranowski, M.P.H., R.D., L.D.* *Children’s Nutrition Research Center, Department of Pediatrics, Baylor College of Medicine, 1100 Bates Street, Houston, Texas 77030-2006; †Division of International Health, Centers for Disease Control and Prevention, 4770 Buford Highway, Mail Stop K26, Atlanta, Georgia 30341; ‡Department of Behavioral Sciences and Health Education, Rollins School of Public Health, Emory University, 1518 Clifton Road, NE, Atlanta, Georgia 30322; and §Department of Family and Preventive Medicine, Emory University School of Medicine, 69 Butler Street, SE, Atlanta, Georgia 30303-3219

Life Sciences Institute (ILSI), initiated a program entitled Physical Activity and Nutrition (PAN) in children and youth by convening a strategic planning workshop. The major objectives of the workshop were as follows: 1. Identify a core set of physical activity and nutrition assessment tools and intervention strategies for children and youth, based upon the current consensus of scientific research and professional practice, that can be applied and further evaluated in community intervention programs; 2. Compile an agenda of future research and other needs, and identify strategies and resources to address those needs; and 3. Provide a synthesis of the current practices regarding nutrition and physical activity assessment and intervention in children and youth. Several teams of researchers who attended the workshop were commissioned to review the literature on the physical activity and dietary practices of children and adolescents, with particular attention to be paid to the burgeoning epidemic of obesity. The content, structure, and internal review of this monograph were coordinated by the CDC under the leadership of Michael Pratt; external editorial review was accomplished under the aegis of Preventive Medicine. The scientists who reviewed the 10 articles in this issue are recognized on the title page. Ultimately, however, this initiative reflects the vision and concern of Alex Malaspina, president of ILSI, who secured the initial funding and engineered the collaborative efforts of ILSI, CDC Foundation, CDC, Emory University, and the many participating scientists. A recent issue of Pediatrics, also funded by ILSI,

Obesity, especially among children, has become epidemic. Even with major advances in genetics, behavior is likely to continue to play a central role in the development of adiposity and obesity. Interventions to help children and adolescents change their dietary or physical activity behaviors may be justified on four grounds: (1) immediate social and health benefits may be obtained; (2) critical periods in childhood may require certain behaviors to lead to healthy outcomes in adulthood; (3) chronic diseases and their elevated risk factors detected in youth may track into the adult years; and (4) the behaviors established in childhood may track into the adult years. Immediate benefits for children (ground 1) and the high tracking of obesity from childhood to the adult years (relates especially to grounds 3 and 4) are the strongest reasons for helping children acquire and retain healthy habits. The nine other papers in this supplemental issue address measurement and intervention issues, with special emphasis on obesity prevention. Reviews of the measurement literature were conducted for diet, nutritional status, physical activity, physical fitness, process evaluation, and environmental factors. Reviews of the intervention literature were conducted for health care providers, schools, and larger community settings. Effective programs for children can and should be designed, implemented, and evaluated. q 2000 American Health Foundation and Academic Press

Key Words: diet; physical activity; obesity; children; genetics; obesity prevention.

BACKGROUND

In October 1996, the Centers for Disease Control and Prevention (CDC), with funding from the International 1 This paper was written while several of the authors were supported by research funding from the National Cancer Institute: CA-61596, CA-73503, and CA-63578. 2 To whom reprint requests should be addressed.

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0091-7435/00 $35.00 Copyright q 2000 by American Health Foundation and Academic Press All rights of reproduction in any form reserved.

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contained a series of articles that emphasized basic science issues in both physical activity and nutrition for children. These articles clearly documented the recent national increase in childhood overweight, with particularly high increases among children at the higher levels of adiposity (1); identified the pervasive negative impact of obesity on mental and physical health, even among children (2); summarized the latest findings on the genetics of obesity (3); and reviewed the available methods for assessing energy expenditure and energy intake (4), psychosocial influences on diet and physical activity among children (5), and what is known about behavioral interventions for treating childhood obesity (6). That issue is essential reading for those interested in understanding what is known about childhood obesity. The present monograph concerns more applied issues in childhood obesity. In the present introductory paper we attempt to integrate the genetic and behavioral perspectives and review the conceptual foundations for why public health agencies should be interested in diet and physical activity among children. We also provide a brief overview of the nine other papers in this issue. GENETICS AND BEHAVIOR IN OBESITY

Adiposity is a person’s amount of body fat. Children in the top 5% of the adiposity distribution are considered overweight, those in the 85th to 95th percentile are considered at risk of overweight [1]. Obesity has not been defined for children, but can be seen as the range of adiposity in adult years where health problems are more likely to occur. In recent years, a paradigm shift that involves genetics has occurred in our explanation of health-related phenomena. Today some see genetics as essential for explaining a disease or condition [3]. From this perspective, obesity is the result of physiological processes that are determined by both genetic and environmental (i.e., anything outside the body) factors and their interrelationships (Fig. 1). Several genes probably contribute in unknown ways to the development of obesity, but genetics alone is likely to be responsible for only a few cases. In some other, much larger but undetermined percentage of cases, genetic and environmental factors interact to result in obesity, and in another large and also unknown percentage of cases, environmental factors are the major contributors.

FIG. 2. Genetic contributions to behavior and adiposity/obesity.

From the behavioral perspective, physical activity and other behaviors are important components of the environment. These behaviors, in turn, reflect genetics as well as larger environmental influences, albeit the genetic factors that affect behavior most likely differ from those that influence physiological processes (Fig. 2). In some cases, where fast food stores are ubiquitous and resources for physical activity (e.g., sidewalks and bicycle paths) are nowhere to be found, the larger environment could be called “toxic” [7]. As suggested by the elements in Fig. 2, even with major advances in genetics, behavior is likely to continue to play an essential role in the development of adiposity and obesity. In the area of genetics, research will likely identify (a) certain aspects of behavior that should be encouraged (e.g., consuming foods that do not trigger adipogenic processes), (b) critical periods during which behavioral interventions may have the greatest chance for effect (e.g., about 6 years of age called adiposity rebound [8], puberty), and (c) which kinds of people might benefit from various behavioral interventions (e.g., people with a specific gene or genes that predispose in known ways to obesity; such persons could be recommended a defined set of behavior changes). Many cases of obesity require that genetic factors interact with behavioral factors, while in many other cases, behavioral factors alone are sufficient. Thus, where interaction is required, the control of behavioral factors should limit the influence of genetic factors. The principal benefit of knowing the genetic factors that influence behavior in a given individual would be the potential tailoring of a behavioral regimen to the relevant genotypic mechanism. The important role of behavior should provide substantial hope for those interested in promoting healthier behaviors to reduce obesity. WHY INTERVENTIONS WITH CHILDREN?

FIG. 1. Traditional genetic model of obesity.

Chronic diseases account for more than half of all mortality in the United States [9]. Obesity is a risk

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factor for many common chronic diseases [2], and several dietary components (e.g., saturated fat, fiber, phytochemicals, antioxidants), as well as low levels of activity, have been related to obesity and associated chronic diseases [3]. Methods of preventing chronic diseases include changing selected lifestyle behaviors (e.g., smoking, diet, physical activity) and reducing risk factors through pharmacological intervention. Preventing chronic disease can be a cost-effective approach to minimizing medical costs and increasing healthy years of life. Several authors have described attempts to change children’s diet and physical activity habits to prevent adult heart disease [10–17] and cancer [10,18–20]. Such dietary and physical activity interventions could be justified in at least four ways [21]: (1) the child might receive immediate health and social benefits; (2) intervention at critical periods in physical growth and maturation in childhood may enhance adult health; (3) modifying chronic disease risk factors in childhood might lead to lower disease rates and risk factors in the adult years; and (4) modifying behavioral preferences or practices in childhood might lead to altered behaviors in adulthood that would afford protection from chronic disease at that time. Evidence in support of each of these justifications is briefly reviewed. Immediate Benefits for Children In children, diet (consumption of macronutrients and micronutrients) has been related to the development and proper functioning of many physiological processes [22,23] and to the prevention of several nutrient deficiency diseases [23]. Children who are healthy are also better prepared to learn; conversely, educational accomplishments and aspirations are linked to health status [2]. Cognitive functioning in general [24] and school performance in particular [25] may be impaired by deficiencies in a child’s diet. Physical activity which promotes low adiposity [26] and the proper functioning of various physiological processes [27,28] is a partial determinant of physical fitness, as measured by cardiovascular and pulmonary function, strength, and body composition [26]. Physical fitness, in turn, enables the performance of many of the personal, school, and other tasks associated with health and healthy functioning in our society [26,29]. In addition, physical activity is related to mental health and emotional status [30,31] which also are primary determinants of optimal functioning. Even children with severe chronic diseases function better with increased levels of physical activity [32]. In the past decade, obesity has become a major health problem in the United States [33]. In its severe form, overweight poses immediate health risks for the child

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by stressing both the metabolic and the skeletal systems [2]; in recent years the prevalence of severe overweight among children has almost doubled. Type 2 diabetes (formerly considered an adult disease) is now also a concern among children [34–37]. Its appearance among youth may be tied to the recent well-documented increase in overweight among children [33,38]. More research is needed to verify this biologically plausible association. Even moderate overweight poses problems for children as they may experience deficits in physical functioning and may find themselves rejected socially causing them emotional distress [2]. As diets high in calories and fat [39] and low levels of activity [33] are associated with overweight, improving the diet and promoting physical activity may minimize this distress among children (more work needs to be conducted in this area) [6]. Critical Periods in Growth and Maturation Inadequate maternal consumption of certain nutrients during critical periods in fetal development, which is evidenced by low birth weight, may contribute to cardiovascular disease in middle and older years [40,41]. Alternatively, baby girls with very high birth weight are predisposed to obesity when they become middle-aged women [41]. Both of these effects are likely related to critical periods in the development of metabolic pathways needed for the proper development of organs and systems [40], but this area of research is controversial, with much more study needed to delineate the pathways of effect [2]. Among children, diet has been related to linear growth (an indicator of skeletal growth) and bone mineralization [22]. In addition, physical activity among children promotes fat-free mass, bone formation and growth, and bone mineralization [26]. Thus, improved diet and physical activity in childhood can have longterm effects on bone health. Children experiencing early physical maturation are likely to become obese as adults [42]. For women, early maturation poses additional risks; e.g., the time between menarche and the end of first pregnancy is a period of rapid growth and differentiation of cells in the breast, at a stage when these cells are particularly susceptible to carcinogenesis [43]. Thus, early consumption of nutrients that protect against cancer and delaying the onset of menarche by increasing physical activity or other means could minimize breast carcinogenesis [43]. A variety of potentially important health-related developmental factors could benefit from interventions among children, but further research is needed to attain more certainty of their existence, strength, and pathways of effects.

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Tracking of Chronic Disease Risk Factors Children rarely die of atherosclerotic heart disease, but fatty streaks in arteries, the earliest stage of this disease, have been detected among children [44] and very young adults [45]. Although young children with early-stage atherosclerotic disease have not been followed into adulthood (in part because arterial fatty streaks cannot now be measured in living persons), it seems likely that their disease progresses as they age. Judging from data among adults, the early development of atherosclerotic disease is likely due in part to diet and physical activity [46], although diet or physical activity interventions have not been shown to induce regression or to retard progression of atherosclerotic disease among children. The third justification for intervention, however, assumes that tracking of risk factors from childhood into the adult years is substantial. The level of tracking between time points a few years apart in childhood that would be high enough to predict with reasonable certainty that tracking will be substantial between childhood and the adult years is not clear. The longer the time interval of concern, the higher must be the value for tracking in youth to assume that a measurement high in childhood (e.g., for adiposity) will be high in adulthood. This third justification for intervention also includes the assumption that risk factors changed in the child years as a result of intervention will track at their new level into the adult years. Twelve-year tracking coefficients (r values) from the Bogalusa study for serum total cholesterol were moderate ranging from 0.38 to 0.64 and varied by ethnicity (African–Americans higher), gender (males slightly higher), and age at initiation of cohort (in general 2- to 8-year-olds had higher coefficients than 9- to 14-yearolds) [47]. Lower 12-year tracking coefficients were obtained for triglycerides (range 0.11 to 0.42), VLDL cholesterol (range 0.24 to 0.45), and HDL cholesterol (range 0.04 to 0.43). Twelve-year tracking coefficients for LDL cholesterol, the dominant atherogenic component of total cholesterol, were moderate (range 0.44 to 0.69). Fiveto 16-year tracking coefficients from the Muscatine study ranged from low to moderate for systolic (range 0.21 to 0.39) and diastolic (range 20.01 to 0.57) blood pressures [48]. In the Muscatine study, tracking coefficients for the quetelet index (an indicator of adiposity) over 5 to 16 years were moderate (range 0.45 to 0.74), with higher coefficients for groups with shorter times between assessments [48]. The correlation between baseline quetelet index and change in this index varied from 0.49 to 0.83, with higher coefficients as time between assessments increased [48], suggesting that heavier children were most likely to become heavier adults. In a French study, 42% of children were in the same quartile of

adiposity at 21 years as at 1 year of age [8], and those most likely to remain in the highest quartile could be predicted by early “adiposity rebound” beginning at about 6 years of age [8]. Finally an integrative review across many published studies showed that 26 to 41% of obese preschool children became obese adults, and 42 to 63% of obese school-aged children became obese adults, with the relative risk for becoming an obese adult being 2 to 6.5 times as high for obese children [49]. Tracking of cardiovascular disease risk factors has been related to changes in diet and physical activity [50]. Diet and physical activity interventions have been demonstrated to promote weight loss and improve chronic disease risk factors [6], among overweight children, but the impact of these interventions on tracking has not been elucidated. In general, dietary and physical activity interventions have improved risk factors primarily among children who already have existing elevated risks [28,51–53], and it is not clear how long the alternatives in risk factors are maintained after the end of behavioral intervention. Still, it seems likely that improved diet and physical activity will delay the onset of a pathologic elevation of risk factors. In summary, while there is evidence for tracking of cardiovascular disease risk factors from childhood to the young adult years, the strongest evidence is for tracking of adiposity. Behavioral interventions have been demonstrated to modify these risk factors and to decrease adiposity. Behavior Tracking The fourth justification assumes that dietary or physical activity practices (behavior) track from childhood into the adult years, when chronic disease is likely to be experienced. There is a common belief that dietary preferences and practices are learned at early ages and carry over into the adult years [15], but the empirical evidence on dietary tracking is sparse. Values for intake of macronutrients have demonstrated moderate 6-year tracking (r 5 0.38 to 0.65) during early childhood [54– 56], and 1-year tracking of servings within food groups among adolescents demonstrated modest to high tracking (r 5 0.25 to 0.70) with tracking highest in the 13- to 15-year age group [57]. Dietary preferences or selections were tracked through much of adolescence, but unfortunately the level of tracking was not identified [58]. Energy intake per kilogram of body weight correlated 0.45 to 0.64 over a 15-year period from 13 to 27 years of age [59], suggesting moderate stability in a risk for obesity over a long period of time. To date, no one has demonstrated tracking from childhood into the adult years for nutrient intakes, dietary practices, or dietary preferences. Some have argued that preference for physical activity and its practice are learned at the earliest ages

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[51]. Others have shown physical activity to track at moderate levels (r 5 0.57) in young children [60] and at generally lower levels (r 5 0.17 to 0.59) through adolescence [61]. Sedentary behavior has also been found to track over 5 years at low to moderate levels (r 5 0.16 to 0.48) from preadolescence to mid-adolescence [62]. Tracking of physical activity from childhood into the adult years has been documented at mostly low to moderate levels (r 5 0.05 to 0.54) [59,61]. Differences in measures, measurement error, and time intervals likely account for much of this variation. The possible tracking of behaviors from childhood into the adult years could be due to any of several mechanisms, including habit, genetics, or stable environment. Quite possibly, much of behavior is a function of habit [63], and so behavior at time 2 is a function of habit at time 2, which in turn reflects behavior and habit at time 1. If true, considerable success could be achieved by simply establishing proper habits at time 1 (e.g., childhood). Social changes, for example, achieving independence from parents, that occur at major life transitions, e.g., the transition out of high school, could affect risk behaviors which would likely minimize tracking from childhood to the adult years [64]. While there is a general age-related decline in physical activity throughout adolescence, levels of such activity drop precipitously at the transition out of high school [64]. In general the effects of life transitions on behaviors and habits deserve more research attention. Because behavior is a function in part of physical environment, social environment, and personal characteristics [66] and genetics [65], stability over time in any one of these factors could help stabilize behavior. Individually, people could engineer stability for themselves by controlling the home availability of foods. In addition, strong positive or negative associations with significant childhood memories (e.g., enjoying holiday foods, a parent’s using a specific dietary behavior) could predispose an adult to perform behaviors consistent with the past memories. There are many such possible mechanisms, and the more that is learned in this area, the more likely interventions can be developed that will have long-lasting effects. The fourth justification makes the assumption that behaviors changed substantially in the child years will track at their new level into the adult years. In a study of elementary school children, dietary change intervention reduced the tracking of dietary behaviors over three annual assessments [67], as would be expected during a change period. Regression to the mean occurred at both ends of the distribution but was more pronounced at the lower end [67]; that is, poorer dietary behaviors became better more often than better behaviors became poorer. It is still not clear to what extent or for how long those with changed dietary practices

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tracked at their new levels. Remarkable fluidity of behavior was detected in that study, with substantial regression to the mean occurring across quintiles from baseline to later assessments. Rationale for Intervention The strongest case for offering behavioral interventions in diet and physical activity to children and adolescents can be made for the first justification: the immediate benefits for children’s health, cognitive abilities, and emotional functioning. It is not clear whether the moderate levels of tracking found by researchers over relatively short periods support the notion that adult practices reflect child practices. As measurement error was probably responsible for many of the low tracking coefficients reported, however, the case should by no means be considered closed. Indeed, this whole area is in need of more research. For example, it is not clear what happens to tracking coefficients during major life transitions, e.g., graduation from high school [64]. More generally, tests of hypotheses about tracking require longitudinal data from childhood to older age. Participants in the major longitudinal child risk factor studies (Bogalusa and Muscatine) are now approaching middle age, but these studies did not begin with a frequency of assessments that was sufficient to reliably assess child diet and physical activity. The strongest case for interventions in children to enhance adult health can be made for initiatives that deal with overweight or obesity, because the coefficients for adiposity tracking are high. This is true partly because more research has addressed this risk factor and partly because adiposity can be measured relatively easily and precisely. Future research on tracking in youth must address whether there are times of higher tracking, the impact of transitions, and the impact of behavioral interventions and how this varies by behavior, region, groups, and so forth. Ideally, all this information will elucidate optimal times for intervention. In conclusion, it appears prudent to encourage dietary and physical activity changes in youth both because of an immediate health benefit to the children and the possibility of a longer-term benefit, especially in regard to overweight. Obesity Prevention The classic public health dilemma is whether prevention activities should be delivered to the general population, targeted at those at high risk, or aimed at both groups, as complementary strategies. Clearly if a child is already obese, treatment of obesity is the intervention of choice, and issues in obesity treatment among children have been delineated [6]. In terms of prevention, because not all people who develop chronic disease are obese, and because non-obese people could benefit from

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increased activity and improved diet, there is every reason to mount broad, population-based preventive programs. Such programs might reduce adiposity for the obese, limit increases in adiposity for the overweight, lower the overall incidence of obesity, and improve protective behaviors against chronic disease for those of normal weight. Such broad-based programs may capitalize on synergy between environmental and personal influences on behavior, but they may also have important shortcomings including substantial cost, difficulties in detecting behavioral outcomes, and the inability to capitalize on obesity-related issues to motivate participants. Interventions targeted at high-risk groups (e.g., children with one or more obese parents, overweight children, and, soon perhaps, children genetically identified as at risk) are an alternative approach to prevention. The primary value of taking this approach is that it directs a program at those most likely to benefit. One caveat is that although it would be possible to try to capitalize on concerns about obesity as motivations to enhance behavior change (much as is done with people with chronic illness), labeling someone as obese involves negative stereotypes and potentially serious emotional reactions which could be counterproductive. Furthermore, because many people who have no obvious risk factors for obesity become obese, targeting the high-risk group will serve only a portion of those in need. Obesity clearly has a multifactorial etiology, including genetic or physiological, behavioral, and environmental factors. The great promise of the genetic revolution is that it will precisely identify causative mechanisms; as these are elucidated, we expect interventions (pharmacologic, behavioral, or environmental) to be developed and tested that address the etiologic factors identified for particular people. Individualized therapy will likely be expensive, but it offers the promise of requiring patients to undertake the minimum number of procedures necessary to control their adiposity. Even with approaches informed by genetics, however, it probably makes sense to make environmental and broad population changes to minimize the incidence of obesity in the first place, with the idea that high-risk programs can be mounted for those not reached by the broader efforts or for whom those efforts do not appear effective. Each community’s leaders and health professionals will need to decide about how best to meet their constituents’ needs, with a particular focus on how to efficiently use available resources. OVERVIEW OF ARTICLES

To guide public health programs for obesity prevention, the rest of this monograph focuses on the practical

issues of measurement and intervention. This issue includes six measurement and three intervention papers. Articles on Measurement McPherson et al. [68] review the validity and reliability of dietary assessment methods among school-aged children. Extensive research on measuring dietary behaviors among adults has provided a foundation for developing assessment strategies for children. Validity and/or reliability studies have been conducted in youth for all of the major dietary assessment techniques: 24h recall, food record, food frequency questionnaire, brief food measure, diet history, and observation. Although food frequency questionnaires generally overestimate energy and several nutrients when compared with a validation standard, the authors find no consistent pattern of validity and reliability for other assessment methods, including food records (often considered a “gold standard” in validation studies). Because there were few validation and reliability studies, further testing of diet-related behavioral instruments is needed, especially of those applicable to a variety of assessment settings and easily adapted to diverse cultural groups and age ranges. Children’s developmental stage and their social influences may be particularly important to consider when targeting dietary assessment. Because children less than age 10 years are largely preliterate and may know relatively little about the packaging, preparation, or type of foods they eat, they will need assistance from parents or other adults who can determine the types, timing, and frequency of foods consumed. Each dietary assessment method has both advantages and disadvantages that need to be considered in selecting a method to use with children. In addition to dietary practices, the assessment of nutritional status among youth includes various anthropometric dimensions that provide information on growth and body composition. Freedman and Perry [69] discuss the importance of accurate anthropometric assessment for examining the nutritional status of children and adolescents, focusing on measurements that can be used in field studies. Valid and reliable measures of height, weight, and body fat are critical for both surveillance and epidemiologic research, particularly for accurately estimating subgroup patterns and temporal trends in obesity and other indicators of nutritional status. The authors concluded there is little evidence that estimates of total body fat, whether based on skinfolds, bioelectrical impedance, dual X-ray absorptiometry, or densitometry, predict various metabolic and clinical complications of obesity better than do simple combinations of weight and height. In contrast, the patterning of body fat is an important risk factor for several chronic diseases and may be considered for use in some studies.

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Kohl et al. [70] critically examine the six major categories of physical activity assessment among children and adolescents: doubly labeled water, direct observation, monitoring, self-report, indirect calorimetry, and direct calorimetry. The validity, reliability, and costs of these measures vary widely. Generally, test–retest and intra-instrument reliability is moderate to high. Measures from validity studies, however, have only low to moderate associations with gold standards. The authors suggest that the range of validity coefficients may indicate that these methods are measuring different properties or components of physical activity (e.g., intensity, frequency, duration, and type of activity), and they indicate that multiple methods may be needed for complete assessment of physical activity. Selection of an appropriate measure of physical activity should consider validity, reliability, and other factors such as the design and purpose of the study and the costs and practicality of the method in a given setting. Although further research needs to clarify the appropriateness of a measure for various characteristics of study populations, the authors found that self-report measures have a been problem in younger age groups. Freedson et al. [71] review the history of fitness testing as well as the fitness test batteries currently used in schools. Such batteries assess cardiorespiratory fitness, flexibility, body composition, and muscular strength and endurance. The rationale for testing has slowly changed from evaluating the fitness of youth toward promoting physically active lifestyles. Both the components of fitness test batteries and the interpretation of test results continue to evolve. Current trends are to use fitness tests to educate youth about physical activity and health and to encourage children to regularly participate in moderate or vigorous physical activity. The systematic development and validation of criterionreferenced standards needs to continue, particularly in the muscular strength, endurance, and flexibility domains, to eliminate the subjectivity that has been common in setting and interpreting such standards. The authors recommend that fitness testing once again be conducted on a nationally representative sample of children and youth so that trends in health-related fitness can be tracked. McGraw et al. [72] review measurement methods for the process evaluation of implementing school-based programs and policies that promote healthy eating and physical activity among youth. Evaluation of program implementation is useful for monitoring progress, refining program elements, and explaining program effects. Approaches to measuring the implementation of key elements of a school-based program, including classroom curricula, food service, and physical activity programs, are reviewed. Quantitative and qualitative aspects of implementation have been delineated. Implementation data have been obtained through archival

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records, self-reported logs or questionnaires, interviews, and trained observers. Methods to evaluate policy adoption and implementation in the school setting include documentation of key decisions made at meetings or other events leading to decisions. More attention must be devoted to consistently defining constructs used to measure implementation [73], assessing the reliability and validity of low-cost measures [74], and linking program implementation to study or program outcomes [73]. A variety of criteria have been proposed to assess the usefulness of measures [75]. Investigators must carefully consider which method provides the greatest benefits and fewest deficits for their purposes. Program staff may wish to consult measurement experts to be sure the most appropriate methods are selected. Children’s diet and physical activity patterns may be affected by environmental factors such as the availability of healthful foods [76] and exercise opportunities in the community, peer preferences for diet and exercise, media messages, and family practices regarding physical activity and food choices [77]. Efforts to measure such factors are relatively new. Richter et al. [78] focus on community-based initiatives, an increasingly popular class of environmental intervention designed to deliver multiple environmental, behavioral, and policy interventions. Input from local citizens and organizations and local control of such initiatives may result in more sustainable interventions that better match community resources and needs. To foster accountability to citizens, grantmakers, and other interested parties, such initiatives should use simple and effective assessment procedures. The authors describe evaluation issues and strategies relevant to developmental phases of community initiatives, from collaborative planning and communication to delivering interventions in multiple settings assessing outcomes and enhancing community capacity to promote health issues. They provide examples of how environmental- and individual-level measures might be integrated to evaluate the effectiveness of such community initiatives and provide an example of one such initiative. Although community initiatives aim to improve citizens’ health through environmental interventions, few have been able to demonstrate whether such interventions have been effective. Articles on Intervention Interventions to prevent obesity usually employ specific channels such as health care providers and schools, and they design specific activities to meet the needs of people in those channels. Health care providers have a high degree of credibility on health issues, and some youth see them regularly. Pediatricians and other professionals give care to young

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people in community-based clinics, private offices, hospitals, schools, and other settings. Sallis et al. [79] review interventions in health care settings to promote healthful eating and physical activity among children and adolescents. Only a few examples of successful interventions exist, and these have focused on short-term behavioral changes (often among obese youth). The authors suggest that research is needed on intensive interventions to produce substantial, long-term behavioral changes in the general population of children and adolescents. Several professional and governmental organizations have advocated routine assessment and counseling of youth and their families about nutrition and physical activity. The authors discuss recommendations and guidelines from these organizations as well as potential strategies for overcoming barriers to counseling by health care providers and other interventions. Wechsler et al. [80] start with a brief review of the usual school-based interventions for promoting physical activity and healthy eating among youth. Next, they more intensively examine how the school environment affects children’s diet and physical activity. They look at recess periods, extracurricular physical activity (particularly intramural), physical activity facilities and equipment, school food services (including vending machines), school policies, and environmental cues and incentives. Many nontraditional possibilities for school interventions are elucidated and sources identified to pursue these possibilities. Interventions can include multiple channels. Pate et al. [81] examine the rationale, theoretical support, and characteristics of community-wide interventions to promote proper nutrition and physical activity in youth. Community-wide programs are needed because youth spend considerable time in community settings outside of school that are conducive to physical activity, and they eat in multiple community settings. Such programs can involve parents and other influential role models. Community health promotion combines community organization and citizen involvement with behavioral or policy strategies for lifestyle or policy intervention. Multiple networks of public and private organizations and delivery may be engaged to coordinate a variety of interrelated and ideally, mutually reinforcing interventions that can be delivered through such diverse channels as the mass media, health care providers, schools, religious institutions, communitybased organizations, worksites, government agencies, and businesses. Although research-based knowledge about the design, implementation, and effectiveness of community-wide intervention programs with children is limited, such strategies are feasible. More research is needed to examine the implementation and effectiveness of community-based initiatives linked to schoolbased interventions.

CONCLUSION

The prevalence of obesity recently accelerated in the United States. Children who become overweight are likely to become overweight adults. Although more research needs to be conducted on how child behaviors evolve into adult behaviors, there is ample justification for conducting dietary and physical activity interventions with children, especially to promote health and prevent obesity. Although more research needs to be conducted to advance the accuracy (validity), precision or reproducibility (reliability), and usefulness of measures of children’s diet and physical activity, a careful assessment of the methods available will result in finding measures that are acceptable given current standards. Acceptable measures of nutritional status and fitness are more commonly available. Community channels provide important opportunities for targeting and evaluating new types of intervention programs, and process evaluation measures enable evaluation of whether programs were implemented appropriately. Although research is needed to identify more effective interventions in health care, school, and community-wide settings, interventions that result in behavior change can be initiated if they are carefully based on relevant theory and developed to reflect specific issues in the various settings. Effective dietary and physical activity change programs for children can be designed, implemented, and evaluated. This collection of papers provides an overview of the status of the field and should assist those trying to develop programs for their communities. ACKNOWLEDGMENTS The discussion of genetics in this paper benefited enormously from conversations with Michael Rosenbaum, M.D., of Rockefeller University and Leann Lipps Birch, Ph.D., of Pennsylvania State University. REFERENCES 1. Troiano RP, Flegal KM. Overweight children and adolescents: Description, epidemiology, and demographics. Pediatrics 1998;101:497–504. 2. Dietz WH. Health consequences of obesity in youth: Childhood predictors of adult disease. Pediatrics 1998;101:518–24. 3. Rosenbaum M, Leibel RL. The physiology of body weight regulation: relevance to the etiology of obesity in children. Pediatrics 1998;101:525–38. 4. Goran MI. Measurement issues related to studies of childhood obesity: Assessment of body composition, body fat distribution, physical activity, and food intake. Pediatrics 1998;101:505–17. 5. Birch LL, Fisher JO. Development of eating behaviors among children and adolescents. Pediatrics 1998;101:539–49. 6. Epstein LH, Saelens BE, Myers MD, Raynor HA. Treatment of pediatric obesity. Pediatrics 1998;101:554–69. 7. Brownell KD. An epidemic of diseases related to diet: Personal or social responsibility. Paper presented at the annual meeting of the American College of Sports Medicine; 1998:125.

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