Recall of recent lunch and its effect on subsequent snack intake

Physiology & Behavior 94 (2008) 454–462

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Physiology & Behavior j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / p h b

Recall of recent lunch and its effect on subsequent snack intake Suzanne Higgs ⁎, Amy C. Williamson, Angela S. Attwood 1 School of Psychology, University of Birmingham, England, UK

A R T I C L E

I N F O

Article history: Received 22 October 2007 Received in revised form 17 January 2008 Accepted 20 February 2008 Keywords: Cognitive Memory Food intake Restraint Disinhibition Palatability

A B S T R A C T Recall of food eaten at lunch decreases afternoon snack intake, suggesting that awareness of a recent eating episode may be an important factor influencing appetite. The aim of the present studies was to investigate whether the inhibitory effect of remembering a recent lunch meal on subsequent snack intake is dependent upon 1) the type and palatability of the snack offered; 2) participants' level of dietary restraint and tendency towards disinhibition; and 3) the delay between lunch and recall. Popcorn snacks differing in amount of added salt and rated palatability were offered to male participants in Experiment 1. Participants who recalled the lunch they had eaten that day consumed less of all types of popcorn than participants who recalled lunch eaten the previous day, suggesting that the effect of recent meal recall is not dependent upon the palatability of the snack food. In Experiment 2, a similar pattern of results was observed but only for women who scored low, and not high, on a measure of tendency toward dietary disinhibition, possibly because a tendency toward disinhibition is associated with impaired memory for the lunch. In Experiment 3, decreased cookie intake by women was observed after remembering today's lunch relative to a neutral control condition, but this effect was similarly only observed for participants scoring low in tendency toward disinhibition. In addition, the effect was dependent on the time elapsed between the lunch and recall, since intake was only reduced at a snack tasting session 3-hours post-lunch (when some forgetting of the meal occurred) and not 1-hour post-lunch. It is concluded that the inhibitory effect of recalling foods eaten at lunch on subsequent snack intake is a robust phenomenon that is related to memory of that lunch and is moderated by tendency toward dietary disinhibition. © 2008 Elsevier Inc. All rights reserved.

1. Introduction The amount of food consumed by people on a single eating occasion is influenced by various cognitive processes such as attention [1–3], beliefs and expectations [4,5], and social knowledge [6]. For example, distracting people from attending to food while eating can increase the amount consumed at a meal [1,2], whereas focusing on eaten food tends to decrease intake [3]. Reduced attention paid to food eaten in the presence of others may also contribute to social facilitation effects on eating [3]. It is well known that eating with other people, especially familiar others, enhances food intake compared to eating alone [7,8], which may be in part due to the distracting effects of the social situation that are moderated by factors such as self-presentation, modelling and social norms [3,9,10]. There is also evidence that manipulating the belief that it is an appropriate time for a meal [4], that a food is high in energy [5], or that an eating episode is a meal rather than a snack [6] can influence food intake in the short-term. ⁎ Corresponding author. School of Psychology, University of Birmingham, Edgbaston, Birmingham, West Midlands, England, B15 2TT, UK. Tel.: +44 121 414 4907; fax: +44 121 414 4897. E-mail address: [email protected] (S. Higgs). 1 Now at: Department of Psychology, University of Bristol, 8 Woodland Road, Bristol BS8 1TN, UK. 0031-9384/$ – see front matter © 2008 Elsevier Inc. All rights reserved. doi:10.1016/j.physbeh.2008.02.011

It has been suggested that another cognitive influence on food intake is memory of recent eating. Supporting evidence comes from studies that have investigated food intake by amnesic patients who are unable to recall eating a recent meal [11–13], and studies of neurologically intact individuals in which participants are reminded of a recent meal [14]. Rozin and colleagues reported that amnesics overeat compared to matched controls when offered multiple meals [12]. One interpretation of these data is that knowledge of recent food consumption is an important influence on meal size since the absence of this knowledge is associated with increased food intake. A prediction therefore arises that facilitating memory of recently eaten food should decrease subsequent intake and indeed it has been reported by Higgs [14] that reminding unrestrained young women of lunch eaten that day by asking them to recall that meal decreases afternoon cookie intake compared with recall of non-food-related information. Furthermore, Higgs [14] found that recall of today's lunch also significantly reduced cookie intake compared with recall of lunch eaten the previous day. Information about the yesterday's lunch intake is likely to be representative of usual food intake rather than the specifics of the eating episode, because information about meals is incorporated quickly into meal schemas [15]. This suggests that the effect of recalling today's lunch on snack intake is not due to recall of food, or even eaten food per se, and is consistent with the involvement of episodic memory for recent eating in the control of food intake.

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The aim of the present studies was to investigate further the effects of recent meal recall on subsequent food intake. Three studies were conducted to examine the influence of 1) snack palatability, 2) individual dietary traits and 3) the time elapsed since lunch on the inhibitory effects of lunch recall. 2. Experiment 1. Recall of today's lunch and subsequent intake of popcorn Experiment 1 investigated whether recall of the last meal decreases intake of three types of popcorn differing only in rated palatability. The reason for offering snacks differing in palatability was twofold. First, it is possible that meal recall reduces snack intake by decreasing the rated pleasantness of the snacks after recall. For example, comparative evaluation of the recalled food and current food in memory could result in a relative devaluation of the snack food, known as consummatory contrast [16] leading to decreased intake. Alternatively, thinking about previously eaten food may draw attention to the sensory characteristics of the snack food, enhancing the usual decline in pleasantness that is observed as a food is eaten known as sensory specific satiety [17]. One way of testing these hypotheses is to investigate whether the inhibitory effect of meal recall is dependent upon the rated palatability of the snack. If meal recall affects snack intake via changes in liking then there should be an interaction of this effect with snack palatability. Second, meal recall has been reported to inhibit intake of cookies at an afternoon tasting session [14]. The use of cookies as the snack food raises the possibility that drawing attention to the fact that a high energy food is being tasted [18], leads participants to reduce their intake because they feel guilty about the high energy food. Therefore, it is important to establish whether the effects of meal recall are specific to tasting particular types of snacks, such as those high in energy, to rule out the possibility that factors such as adherence to social norms regarding the consumption of high energy foods provide alternative explanations for the results [19]. 2.1. Method 2.1.1. Participants The participants were 14 young healthy male students (mean age = 21, standard error of the mean (SEM) = 0.7, mean body mass index (BMI) = 22.5 kg/m2, SEM = 0.6), who were recruited from a database of volunteers maintained by the Eating Behavior Laboratory at the University of Birmingham and posters on campus. Standard exclusionary criteria were self-reported diabetes or food allergies (to avoid adverse reactions to the test foods), self-reported cigarette smoking (due to effects of nicotine on appetite), or a BMI outside of the normal range (19–25 kg/m2). The initial sample comprised the first 17 volunteers who met the study's requirements. Three participants were subsequently excluded because on arrival for testing they reported that they did not like popcorn. So that participants were not alerted to the purpose of the experiment, and to guard against expectancy/demand effects, the study was described as an investigation of food preferences. Participants gave informed written consent prior to participation and were paid £6 Stirling. The study protocol was approved by the Intramural Ethics Committee and the study was conducted according to the ethical standards laid down in the Declaration of Helsinki 1964. 2.1.2. Experimental design Participants took part in two experimental conditions according to a repeated-measures design: 1) the Lunch Today condition, in which they were asked to recall what they had eaten for lunch that day immediately before tasting and rating the afternoon snack; and 2) the Lunch Yesterday condition in which they were asked to recall what they had eaten for lunch the previous day immediately before tasting

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and rating the afternoon snack. Approximately half the sample completed the Lunch Today condition followed by the Lunch Yesterday condition (n = 8) and the rest completed the Lunch Yesterday followed by the Lunch Today condition (n = 6). Participants were asked to consume their lunch at least 2 h before the test session on both test days and 3–7 days elapsed in between the test sessions. 2.1.3. Eating behavior and mood measures The participants' eating behavior was assessed via a “lifestyle” questionnaire that was sent as part of the recruitment process and included scales assessing dietary restraint and tendency toward disinhibition. Dietary restraint is the conscious determination and effort to restrict food intake and calories to control body weight and the restraint scale of the Dutch Eating Behavior Questionnaire (DEBQ) [20] is a frequently used instrument to measure dietary restraint. It consists of 10 items (e.g. “When you have put on weight do you eat less than you usually do?”, “Do you deliberately eat foods that are slimming?”, “Do you deliberately eat less in order not to become heavier?”, “Do you take your weight into account with what you eat?”) having a five-option response format: never (1), seldom (2), sometimes (3), often (4), and very often (5). A restraint score is obtained by summing the scores for the 10 items and dividing by 10. The DEBQ restraint scale was chosen because the internal consistency and factorial validity of this scale is well established and it has greater internal consistency and a more stable factor structure compared with the other scales such as the restraint scale of the Three Factor Eating Questionnaire (TFEQ) [21]. Participants were categorised as low in restraint if they scored 2.3 or less on this scale. This score is the median score for European populations [22]. The mean DEBQ restraint score for the group was 1.6 (SEM = 0.1). Participants were also completed the disinhibition scale of the TFEQ [23] which measures tendency to overeat in certain situations and has been shown to be related to tendency toward overeating in the laboratory [24]. This scale consists of 13 items (e.g. “I usually eat too much at social occasions, like parties and picnics”, “Sometimes when I start eating, I just can't seem to stop”, “Sometimes things just taste so good that I keep on eating even when I am no longer hungry”) having a True/False response format, and three items (e.g.” Do you eat sensibly in front of others and spurge alone?”) having a four-option response format: never (1), rarely (2), often (3), always (4). Responses are scored 0 or 1 and summed. and their mean disinhibition score was 4.4 (SEM = 0.6). Although tendency toward disinhibition has been assessed by other researchers using combined scores on the External and Emotional scales of the DEBQ [25], we adopted a more straightforward approach to measuring tendency toward disinhibition and used the single disinhibition scale of the TFEQ [26]. Participants' self-reported appetite and mood at the test sessions were measured using a 100 mm unmarked line rating scales with “Not at all” and “Extremely” as end anchors and the question “How XXX do you feel right now?”: hungry, full, thirsty, bloated, anxious, cheerful, stressed and headachy (centred above the line). The participant also rated his current desire to eat using a similar line rating scale anchored with “Not at all strong and “Extremely strong”. Appetite ratings were obtained by measuring the distance in mm from the left extremity of the rating lines. 2.1.4. Procedure Before the study, participants were informed via email that they would be taking part in a food tasting session. They signed up for a 30-min slot between 2.30 and 4.30 and were tested individually. Upon arrival, the participant was seated at a table in a quiet room and asked to complete the rating scales assessing mood and appetite. Participants in the Lunch Today condition were then given a sheet of A4 paper and asked to “write down in as much detail as possible what you ate for your lunch today”. Participants in the Lunch Yesterday condition were asked to “write down in as much detail as possible

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what you ate for your lunch yesterday” on the piece of paper provided. In both conditions, participants were told they had 5 min to complete the task during which time the experimenter would not be present. When the experimenter returned, line rating scales assessing hunger, fullness, desire to eat and mood were completed. Participants then completed the popcorn taste test. This was the same for all participants regardless of the assigned condition. Three bowls of popcorn were placed on the table. Popcorn was chosen as the snack because the palatability of the popcorn can be manipulated without altering the energy content by adding differing amounts of salt. The three types of popcorn offered were, high salt (1 teaspoon salt added per 100 g), low salt (1/2 teaspoon salt added per 100 g) and no salt. The bowls were labelled A, B, and C. The popcorn was prepared freshly every day from corn kernels (Dunn's River natural popping corn) using a popcorn maker (Prima PDP100 Duck Popper Popcorn Maker, UK). The quantity of popcorn provided allowed a considerable amount to be eaten without the bowls appearing empty. This was to ensure that participants would not restrict the amount eaten based on whether the experimenter could see how much had been consumed. A glass of tap water was also provided. The participant was instructed to taste and rate each type of popcorn (the order of presentation of the bowls was randomised across participants) using the sheets provided (one for each popcorn type). The participant was asked to rate each type of popcorn in terms of how pleasant the taste was and how salty, sweet, and sour tasting it was using 100 mm unmarked line rating scales anchored by “not at all” and “extremely”. They also rated how often they would choose the popcorn using the same line rating scale anchored “never choose” and “always choose”. These ratings were made while the participant was eating the popcorn. In line with the study being an investigation about food preferences, the importance of giving accurate ratings was emphasised and the participant was told to eat as little or as much popcorn as was necessary to achieve such a rating. Lastly, the participant was informed that on completion of the ratings he was free to help himself to any popcorn left over if he so wished but asked not to change his original ratings. The participant was informed he had 10 min to complete these ratings and was then left alone for this time. Following the popcorn taste test a final set of line rating scales assessing hunger, fullness and desire to eat and mood was completed. At the end of the session, the participant's weight and height were measured and a post-experimental questionnaire asking the participant what he thought the experiment was about and whether there was anything he thought would have affected his food intake that day (e.g. illness) was completed. Finally, participants were asked to refrain from telling others about the experiment, thanked for their participation and told that debriefing would be by email. The amount of each type of popcorn consumed by each participant was calculated using successive weighing of the bowls of popcorn. 2.1.5. Analysis Popcorn intake and liking was analysed using ANOVA with condition (Lunch Yesterday/Lunch Today) and popcorn type (no salt, low salt, and high salt) as within-subjects factors. To check for order effects, condition order (Lunch Today first versus Lunch Yesterday first) was added as a between-subjects factor to the ANOVA but this did not change the outcome (data not reported). Baseline (pre-recall) ratings of hunger, fullness and desire to eat and pre- to post-recall changes in these ratings were analysed by paired samples t-tests (two-tailed). Statistical analyses were by SPSS 15.0 for Windows. A result was considered statistically significant if p b 0.05. 2.2. Results and discussion 2.2.1. Manipulation check Although it was not possible to independently verify what the participants had actually eaten for their lunch that day or the previous day, in both the Lunch Today and Lunch Yesterday conditions

participants wrote down detailed food-related information that was consistent with the manipulation. The post-experimental questionnaire also confirmed that no participant had second-guessed the purpose of the study. The majority of participants wrote that they thought the study was about the effects of food on mood. Three participants mentioned memory when asked to write down their thoughts on the purpose of the study. However, there was no indication that these participants were aware of the study hypotheses. One participant said they thought the study was about the effects of “hunger on mood and memory”, one participant said they thought the study was about “flavours of popcorn and how they make you remember other flavours” and one participant said they thought the study was about “the effect of food on memory”. 2.2.2. Rated hunger, fullness and desire to eat 2.2.2.1. Baseline ratings. There was no effect of condition on pre-recall appetite ratings. There were no significant effects of condition on rated hunger (t (13)= 0.3, p N 0.05, Lunch Today: mean= 53.1, SEM = 5.4; Lunch Yesterday: mean= 50.9, SEM. = 6.6), fullness (t (13)= 1.3, p N 0.05, Lunch Today: mean= 36.5, SEM = 5.2; Lunch Yesterday: mean= 28.3, SEM = 5.1), or desire to eat (t (13) = −0.4, p N 0.05, Lunch Today: mean = 51.9, SEM= 4.8; Lunch Yesterday: mean= 57.1, SEM= 6.4). 2.2.2.2. Pre- to post-recall changes. There was no effect of condition on the change in hunger, fullness, or desire to eat ratings observed after recall (all p N 0.05, Table 1). 2.2.3. Popcorn intake ANOVA revealed a significant main effect of condition, F(1, 13) = 6.5, p b 0.05. Participants ate significantly less popcorn in the Lunch Today compared with Lunch Yesterday condition. There was also a significant main effect of popcorn type, F(2, 26) = 4.8, p b 0.05, but no significant interaction between condition and popcorn type, F(2, 26) = 0.03, p N 0.05 (Fig. 1). Post-hoc testing revealed that both the salted types of corn were consumed significantly more than the non-salted corn (p b 0.05) but there was no difference in consumption of the two types of salted corn. 2.2.4. Popcorn preference and rated pleasantness There was a main effect of popcorn type for rated pleasantness of the flavour of the popcorn, F(1, 13) = 9.0, p b 0.01: rated pleasantness increased with increasing added salt. There was no effect of condition, F(1, 13) = 0.44, p N 0.05, but there was a significant condition × popcorn type interaction, F(1, 13) = 6.2, p b 0.05. However, post-hoc t-tests did not reveal any significant effect of condition on rated liking of each popcorn type. The pattern of data suggests that for the Lunch Yesterday condition, there was a tendency for the most salted popcorn Table 1 Pre- to post-recall changes in rated appetite and popcorn pleasantness and choice in Experiment 1 as a function of popcorn type and experimental condition Rating (mm)

Lunch Today (n = 14)

Lunch Yesterday (n = 14)

Pre- to post-recall change in hunger Pre- to post-recall change in fullness Pre- to post-recall change in desire to eat Popcorn pleasant Taste (0–100) No salt Low salt High salt Popcorn choice (0–100) No salt Low salt High salt

−3.3 (2.6) 7.5 (3.4) −3.6 (4)

−8.6 (2.4) 5.5 (2.8) −6.1 (3)

28.6 (3.3) 46.0 (5.3) 55.5 (5.0)

35.7 (5.0) 55.2 (4.0) 45.9 (6.2)

19.7 (6.2) 45.5 (6.4) 58.9 (3.8)

28.0 (6.4) 55.7 (4.52) 46.5 (6.3)

Data are presented as mean (standard error of the mean).

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disinhibition show greater reactivity to food-related cues [27–29] and so it is possible that participants with high levels of dietary restraint and tendency toward disinhibition are more responsive to the effects of meal recall on subsequent intake. Alternatively, because working memory capacity has also been shown to be impaired in dieters with a tendency towards disinhibition [30–32] it is possible that due to impaired encoding and/or retrieval of lunch-related memories such individuals are less responsive to the effects of lunch recall on subsequent intake. Therefore, in Experiment 2, we examined the effect of recalling today's versus yesterday's lunch on afternoon popcorn intake in participants who varied in their dietary traits. To identify the specific roles that restraint and tendency toward disinhibition might have to play in moderating the response to lunch recall we assessed these traits separately using the Dutch Eating Behaviour Questionnaire restraint scale [20] and the disinhibition scale of the Three Factor Eating Questionnaire [23]. Fig. 1. Intake of popcorn differing in added salt as a function of condition in Experiment 1. Data are shown as mean intake (g) + SEM, N = 14.

to be rated as slightly less pleasant than the medium salted popcorn, whereas for the Lunch Today condition there was a linear relationship between rated pleasantness and added salt. A similar pattern of results was observed for ratings of how often participants said they would choose the popcorn (main effect of popcorn, F(1, 13) = 11.5, p b 0.01, no main effect of condition , F(1, 13) = 0.32, p N 0.05, but a significant condition × popcorn interaction F(1, 13) = 5.7, p b 0.01) (Table 1). In this experiment, we investigated the effect of meal recall on intake of popcorn differing in added salt and rated pleasantness. We found that when participants were asked to recall lunch eaten that day, intake of all three popcorn types (no salt, low salt and high salt) was reduced compared with a condition in which lunch eaten the previous day was recalled. Furthermore, we found that there was no effect of Lunch Today recall on hedonic ratings of the popcorn. These data suggest that the inhibitory effect of recalling recent eating on subsequent intake is not related to changes in the hedonic evaluation of food [16,17] and is independent of the mechanisms underlying palatability responding. Furthermore, the results suggest that the inhibitory effects of meal recall on snack intake are not restricted to consumption of a high energy food such as cookies and therefore are unlikely to be mediated by adherence to social norms regarding the consumption of high energy foods. 3. Experiment 2. Recall of today's lunch and subsequent snack intake: effects of dietary restraint and disinhibition The aim of Experiment 2 was to investigate whether the effect of meal recall on snack intake is dependent upon individual dietary traits, in particular, the tendency to consciously restrict food intake (dietary restraint) [20] and the tendency to overeat in specific situations such as those in which tempting food is present or there are other people eating [23]. Dieters with a tendency towards

3.1. Method 3.1.1. Participants The participants were 73 young healthy female students (mean age 20 years, SEM = 0.2, mean BMI 21 kg/m2, SEM = 0.17) who were recruited from a database of volunteers maintained by the Eating Behavior Laboratory at the University of Birmingham and posters on campus. Participants were excluded from participating if they selfreported having diabetes or food allergies, were smokers, or had a BMI outside of the normal range (19–25 kg/m2). The initial sample comprised the first 75 volunteers who met the study's requirements, two participants were subsequently excluded because they reported feeling ill on one of the test days. So that participants were not alerted to the purpose of the experiment, and to disguise the hypothesis under test, recruitment to the study was via email/posters describing the experiment as an investigation of the effect of food on mood. Participants gave informed written consent prior to participation and were paid £6 Stirling. The study protocol was approved by the Intramural Ethics Committee and the study was conducted according to the ethical standards laid down in the Declaration of Helsinki 1964. 3.1.2. Experimental design A between-subjects design was used in which immediately before the snack tasting session, half the sample were asked to recall the lunch they had eaten that day (Lunch Today condition) and the other half were asked to recall the lunch they had eaten the previous day and to write these thoughts down (Lunch Yesterday condition). Dietary restraint and tendency toward disinhibition scores were gathered by responses to a lifestyle questionnaire that was emailed before the test session. Dietary restraint was determined using the restraint scale of the Dutch Eating Behaviour Questionnaire (DEBQ) [20]. Tendency toward disinhibition was assessed using the disinhibition scale of the Three Factor Eating Questionnaire [23] as described for Experiment 1. Participants were allocated to one of four groups (Low Restraint/Low Disinhibition (LR/LD), Low Restraint/High

Table 2 Participant characteristics as a function of condition, dietary restraint and disinhibition Lunch Today condition

Age (years) BMI Restraint (DEBQ) Disinhibition (TFEQ)

Lunch Yesterday condition

LR/LD (N = 10)

HR/LD (N = 10)

LR/HD (N = 7)

HR/HD (N = 9)

LR/LD (N = 11)

HR/LD (N = 10)

LR/HD (N = 6)

HR/HD (N = 10)

19.8 (0.6) 20.5 (0.5) 1.5 (0.2) 4.4 (0.6)

19.7 21.5 2.7 5.4

20.37 (0.7) 20.9 (0.5) 1.8 (0.2) 9.0 (0.7)

20.2 (0.7) 21.7 (0.5) 3 (0.1) 10.7 (0.68)

20.2 (0.6) 20.8 (0.4) 1.6 (0.1) 4.2 (0.6)

20.6 (0.6) 21.3 (0.5) 2.5 (0.2) 4.6 (0.6)

20.0 21.4 1.9 10.5

19.5 (0.6) 21.61 (0.5) 3.2 (0.2) 11.1 (0.6)

(0.6) (0.5) (0.2) (0.6)

(0.8) (0.6) (0.2) (0.7)

Values are expressed as mean (SEM). LR/LD = low restraint/low disinhibition, HR/LD = high restraint/low disinhibition, LR/HD = low restraint/high disinhibition, HR/HD = high restraint/high disinhibition. DEBQ = Dutch Eating Behaviour Questionnaire [20]. TFEQ = Three Factor Eating Questionnaire [23].

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Disinhibition (LR/HD), High Restraint/Low Disinhibition (HR/LD), High Restraint/High Disinhibition (HR/HD)) based on cut off scores of 2.3 for the DEBQ dietary restraint scale and 8 for the TFEQ disinhibition scale [26]. To ensure roughly equal numbers in experimental conditions participants were first categorised according to their restraint/ disinhibition status and then randomly allocated to either the lunch today or lunch yesterday group (see Table 2). 3.1.3. Procedure The procedure was as for Experiment 1, except that before taking part in the main test, participants attended an introductory session at which they tasted and rated the popcorn. This was to familiarise them with the test setting and procedure and to obtain a baseline measure of snack intake for the experimental groups. Participants were instructed to eat their lunch at least 2 h prior to the test session. 3.1.4. Analysis To check for baseline differences, popcorn intake on the introductory day was analysed by univariate ANOVA with condition (Lunch Yesterday/Lunch Today), restraint (High Restraint/Low Restraint) and disinhibition (High Disinhibition/Low Disinhibition) as betweensubjects factors. Participant characteristics were analysed by ANOVA with condition, restraint and disinhibition as group factors. For the test days, popcorn intake and liking was analysed using ANOVA with popcorn type (no salt, low salt, and high salt) as a within-subjects factor and condition (Lunch Yesterday/Lunch Today), restraint and disinhibition as between-subjects factors. Baseline (pre-recall) ratings of hunger, fullness and desire to eat and pre- to post-recall changes in these ratings were analysed by ANOVA with condition and restraint and disinhibition as factors. Statistical analyses were by SPSS 15.0 for Windows. A result was considered statistically significant if p b 0.05.

F(1, 65) = 6.8, p b 0.5, and desire to eat ratings, F(1, 65) = 7.7, p b 0.5, whereby the low disinhibition participants reported being more hungry and having a greater desire to eat before recall in the Lunch Today condition compared with the Lunch Yesterday condition. 3.2.3.2. Pre- to post-recall changes. There was no effect of condition on the change in hunger, fullness, or desire to eat ratings after recall (all p N 0.05). 3.2.4. Popcorn intake Analysis of the popcorn intake on the introductory day revealed that the groups did not differ in terms of their baseline intake, F(1, 65) = 0.8, p N 0.05 (mean popcorn intake for the Lunch Today condition= 14.0 g; mean popcorn intake for the Lunch Yesterday condition = 14.0 g), nor were there any significant interactions between condition and restraint or condition and disinhibition at baseline. For the test sessions, there was a significant main effect of popcorn type, F(2, 130) = 21, p b 0.01, whereby intake of the highest salted corn was significantly greater than the medium salted and non-salted corn (ps b 0.01). There were no significant main effects of condition, F(1, 65) = 0.6, p N 0.05, restraint, F(1, 65) = 0.3, p N 0.05, or disinhibition F(1, 65) = 0.6, p N 0.05, on popcorn intake. However, there was a significant interaction between condition and disinhibition, F(1, 65) = 4.9, p b 0.05. Posthoc analysis showed that there was a significant decrease in intake in the Lunch Today compared with the Lunch Yesterday conditions, but only for low disinhibition participants (p b 0.05). There were no other significant interactions (all p N 0.05) (Fig. 2). Because there were differences in rated hunger before the recall period, this hunger rating was added as covariate in the ANOVA but the interaction between

3.2. Experiment 2: results and discussion 3.2.1. Manipulation check All participants in both conditions wrote down detailed foodrelated information consistent with the manipulation. The postexperimental questionnaire also confirmed that no participant had second-guessed the exact purpose of the study. 3.2.2. Participant characteristics ANOVA revealed that for age and BMI, there were no main effects of condition, tendency toward disinhibition, or restraint and no significant interactions (all p N 0.1). For restrained eating, there was a main effect of group whereby the high restraint groups had significantly higher DEBQ restraint scores compared with the low restraint groups F(1, 65) = 66, p b 0.01, but there was no significant effect of condition and no significant group × condition interaction (all p N 0.05). Similarly, for tendency toward disinhibition scores, there was a main effect of group whereby the high disinhibition groups had significantly higher TFEQ disinhibition scores compared with the low disinhibition groups (1, 65) = 60, p b 0.01, but there was no significant effect of condition on disinhibition and no significant group × condition interaction (all p N 0.5) (Table 2). 3.2.3. Rated hunger, fullness and desire to eat 3.2.3.1. Baseline ratings. There were no differences in pre-recall rated fullness between the Lunch Today and Lunch Yesterday conditions, or as a function of tendency toward disinhibition or restraint (all p N 0.05). There was a significant main effect of restraint on hunger, F(1, 65) = 4.4, p b 0.05, whereby the restrained participants reported being less hungry than the unrestrained participants (mean hunger rating restrained = 49.6, SEM = 3.6; mean hunger rating unrestrained = 60.8, SEM = 3.9). There was also a significant interaction between tendency toward disinhibition and condition, for both hunger,

Fig. 2. Intake of popcorn differing in added salt as a function of condition for A) low disinhibition (N = 32) and B) high disinhibition participants (N = 41) in Experiment 2. Data are shown as mean intake (g) + SEM.

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disinhibition and condition remained, F(1, 65) = 4.8, p b 0.05, and no other significant effects emerged. 3.2.5. Popcorn preference and rated pleasantness There was a main effect of popcorn type for rated popcorn pleasantness, F(2, 130) = 10.8, p b 0.01 and post-hoc tests showed that both salted types of corn were rated as significantly more pleasant than the non-salted corn (ps b 0.01) (mean rating for no salt popcorn = 37.6, SD = 2.3; mean rating for low salt popcorn = 48.0, SD = 2.8; mean rating for high salt popcorn = 52.7, SD = 3.2). There were no main effects of condition, F(1, 65) = 1.5, p N 0.05, restraint F(1, 65) = 1.5, p N 0.05, or disinhibition F(1, 65) = 0.17, p N 0.05, and no significant interactions (all p N 0.05). A similar pattern of results was observed for ratings of how often participants said they would choose the popcorn (main effect of popcorn: F(2, 130) = 18.2, p b 0.01). In this experiment, we examined associations between measures of dietary restraint and tendency towards disinhibition and responses to meal recall. We found no evidence that dietary restraint affected the response to meal recall. However, only participants scoring low and not high in tendency toward disinhibition as measured by the TFEQ disinhibition scale [23] decreased their snack intake after thinking about a recent meal. The difference in snack intake between participants scoring low and high on the TFEQ disinhibition scale is not due to the latter group having a higher BMI because the groups did not differ in BMI. Neither can the results be explained by baseline differences in appetite because we found no relationship between these measures and snack intake. It is also unlikely that any effect of meal recall was masked because the snacks triggered overeating in participants with a tendency to disinhibit [33–35], because we did not find that the high disinhibition group ate more snacks overall than the low disinhibition group. Alternatively, it is possible that meal recall had no effect in participants scoring high on the disinhibition scale because encoding or retrieval of memory of their lunch was impaired, thus reducing the effectiveness of the manipulation. In support, dieters with a tendency towards disinhibition have been shown to exhibit impairments in working memory that are related to preoccupying thoughts of food and body shape [32]. Therefore, the participants in our studies with a tendency towards disinhibition may have been distracted by such thoughts and this interfered with encoding or retrieval of the lunch. As this hypothesis is speculative, we decided to find out if the effect could be replicated in Experiment 3. 4. Experiment 3. Recall of today's lunch and subsequent snack intake: effect of time elapsed since the lunch The primary aim of Experiment 3 was to test the hypothesis that the effect of meal recall on snack intake is dependent upon memory, as opposed to some non-memory related effect of the cueing procedure. The inclusion of a delay between a prior event and a later task is typical in memory testing and the decrease in performance found with increasing delay describes the forgetting function [36]. Therefore, in Experiment 3 we examined whether the effect of meal recall is time dependent. Participants recalled either their lunch eaten that day or their journey to the test session that day and the effect on cookie intake was measured after a short delay (1-hour post-lunch, and a longer delay (3-hours post-lunch). We predicted that compared with a short interval, a longer interval between lunch and recall would result in more forgetting of the meal and hence a stronger effect of the reminder. Based on the results of Experiment 2, we also assessed whether the effect of meal recall is moderated by dietary traits. 4.1. Method 4.1.1. Participants The participants were 47 healthy young female students (mean age = 22.0, SEM = 0.4 years, mean BMI = 22.0 kg/m2, SEM = 0.3) who

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were recruited from a database of volunteers maintained by the Eating Behavior Laboratory at the University of Birmingham and posters on campus. Participants were excluded from participating if they selfreported having diabetes or food allergies, were smokers, or had a BMI outside of the normal range (19–25 kg/m2) or were not habitual breakfast eaters (to control for intake prior to the controlled lunch). The sample comprised the first 47 volunteers who met the study's requirements. So that participants were not alerted to the purpose of the experiment, recruitment to the study was via email/posters describing the experiment as a study of “food on mood”. Participants gave informed written consent prior to participation and they were paid £10 Stirling. The study protocol was approved by the Intramural Ethics Committee and the study was conducted according to the ethical standards laid down in the Declaration of Helsinki 1964. 4.1.2. Experimental design A mixed within- and between-subjects design was used in which immediately before the snack tasting session, half of the sample were asked to recall the lunch they had eaten that day (Lunch Today condition) and the other half were asked to recall their journey to the University Campus (Journey control condition). Within each of these groups, participants attended two test days: on one test day, they returned to the laboratory for the taste test 1 h after they had consumed lunch in the laboratory and on the other test day, they returned to the lab 3 h after they had eaten the lunch in the laboratory. Participants were randomly allocated to the experimental conditions and then within each condition (Lunch Today versus Journey condition) the order of test days (1 h versus 3 h) was randomised so that approximately equal numbers of participants experienced the 1hour followed by the 3-hour test and the remaining participants experienced the tests in the other order. 4.1.3. Procedure Prior to the test days, participants were invited to attend an introductory session at which they tasted and rated the cookies that would be consumed in the main experiment. This was to familiarise them with the test setting and procedure and to obtain baseline measures of cookie intake. At individual sessions, the participants were presented with three plates of cookies containing a different variety, labelled A, B and C. The three types of cookies were digestives (McVitie, UK, 495 calories per 100 g), crinkle crunch (Fox's, UK 470 calories per 100 g) and Hobnobs (McVitie, UK 466 calories per 100 g). The quantity of cookies provided (15 cookies of each broken into quarters) allowed for a considerable amount to be eaten without the plates appearing empty to ensure that participants would not restrict the amount eaten based on whether the experimenter could see how much had been consumed. A glass of tap water was also provided. The participant was asked to rate each cookie in terms of how pleasant the taste was and how salty, sweet, and sour it was using 100 mm unmarked line rating scales anchored by “not at all” and “extremely”. These ratings were made while the participant was eating the cookie. The participants were told that could eat as many cookies as they wished after they had finished their ratings as there was an unlimited supply and they were left alone for 10 min to complete the task. At the end of the introductory session, the participant's weight and height were measured and a questionnaire asking about their age and eating habits was completed. This questionnaire included the restraint scale of the DEBQ [20] and the disinhibition scale of the TFEQ [23]. There were two test days each comprising two sessions: a lunch session and a snack tasting session. The first session (lunch session) took place between 12.00 and 1.30 p.m. and this was the same for all participants. On one of the test days, the participant was then required to return to the laboratory 1 h after lunch for the second session, and on the other test day she was required to return 3 h later. Approximately half the participants completed the 1-hour delay test first and the other half completed the 3-hour delay test first.

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Upon arrival for the first test session (the lunch session), the participant was seated individually at a table in a quiet room and asked to complete a series of unmarked line rating scales assessing mood and appetite. The following items were rated using a 100 mm line rating scale with “Not at all” and “Extremely” as end anchors and the question “How XXX do you feel right now?”: hungry, full, thirsty, bloated, friendly, headachey, drowsy (centred above the line). The participant also rated her current desire to eat using a similar unmarked line rating scale anchored with “Not at all strong” and “Extremely strong” and was asked write down what she had eaten for breakfast. Immediately after this, the participant was presented with lunch, which consisted of white bread cream cheese sandwiches (made with two slices of bread (Sainsbury, UK) and spread with cream cheese (Philadelphia, Kraft Foods, UK) cut into quarters) and a packet of ready salted potato chips (Walkers Crisps, UK). To disguise the portion size provided, the crisps were presented in a bowl. The lunch meal contained approximately 400 calories. While she was consuming the lunch, the participant was asked to rate how much she liked the taste of each lunch items (crisps and sandwiches) (“How pleasant is the flavour of XXX?” anchored “not at all pleasant” and “extremely pleasant”) and how often she would choose to eat the lunch item (“Would you choose to eat XXX?”, anchored “never choose ” and “always choose”). Once she had consumed all of the lunch, further ratings of hunger, fullness desire to eat and mood were taken. The participant was then thanked and reminded to return promptly for the afternoon session. She was asked to refrain from eating and drinking anything apart from water until the after the second session, and was given a 500 ml bottle of mineral water to take away. At the beginning of the second test session (the snack taste test), the participant was asked to rate her hunger, fullness, desire to eat and mood using the line rating scales described previously. Participants in the Lunch Today condition were then asked to think about the lunch they had eaten that day and to write down their thoughts about the lunch in as much detail as possible. Participants in the Journey condition were asked to write down in as much detail as possible their thoughts about their journey to the University campus that day. Further ratings of hunger, fullness and desire to eat were then completed, immediately followed by the taste test, which was the same as that completed as part of the introductory session. After the taste test, the experimenter returned and another set of line rating scales was completed (assessing hunger, fullness desire to eat and mood). On the final test day, the participant was asked to write down her thoughts on the purpose of the experiment. She was then thanked and told that debriefing would be by email. The amount of cookies consumed by each participant was calculated by weighing the plates before and after the taste test. 4.1.4. Analysis To check for baseline differences, cookie intake on the introductory day was analysed by univariate ANOVA with condition as a betweensubjects factor (Journey/Lunch Today). Because previous results suggested that the effect of condition might be influenced by individual differences in eating behavior we also included dietary restraint (High Restraint/Low Restraint) and disinhibition (High Disinhibition/Low Disinhibition) as between-subjects factors. The cut off values for categorisation of restraint and disinhibition were as described previously. Participant characteristics as a function of condition were analysed by independent t-tests. Cookie intake and liking on the test days was analysed using ANOVA with time since lunch (1 h/3 h) and cookie type (hobnobs, crinkle crunch and digestives) as within-subjects factors and condition (Lunch Today/ Journey), restraint (High Restraint/Low Restraint) and disinhibition (High Disinhibition/Low Disinhibition) as between-subjects factors. To check for order effects, condition order (1-hour delay first versus 3-hour delay first) was added as a between-subjects factor to the

ANOVA but this did not change the outcome (data not reported). Baseline and pre- to post-recall changes in rated hunger, fullness and desire to eat were analysed using ANOVA with time since lunch, condition and restraint and disinhibition as factors. Statistical analyses were by SPSS 15.0 for Windows. A result was considered statistically significant if p b 0.05. 4.2. Experiment 3: results and discussion 4.2.1. Manipulation check All participants ate all of the lunch. All participants in the Journey condition wrote down thoughts about their journey to university and did not mention thoughts of food or lunch. All but one participant in the Lunch Today condition wrote down thoughts about their lunch. One participant wrote down what she would like to eat rather than what she had eaten for lunch and she was excluded from the analysis. The post-experimental questionnaire also confirmed that no participant had second-guessed the exact purpose of the study. The majority of participants said that they thought the study was about food and mood (in line with the cover story). One participant mentioned that they thought the study was about “memory recall and when you ate lunch” suggesting that they thought the study was about the effect of lunch on memory rather than the effect of memory for lunch on snack intake. 4.2.2. Participant characteristics Independent t-tests confirmed that participants in Lunch Today versus Journey conditions did not differ in terms of their age (t = 0.3, p N 0.05, Journey: mean = 22.4, SEM = 0.7; Lunch Today: mean = 22.2, SEM = 0.5), BMI (t = 1.6, p N 0.05, Journey: mean = 22.4, SEM = 0.4; Lunch Today: mean = 21.5, SEM = 0.4), DEBQ restraint scores (t = −0.4, p N 0.05, Journey: mean = 2.5, SEM = 0.19; Lunch Today: mean = 2.3, SEM = 0.19), or TFEQ disinhibition scores (t = −0.2, p N 0.05, Journey: mean = 5.7, SEM = 0.6; Lunch Today: mean = 5.6, SEM = 0.7). 4.2.3. Rated hunger, fullness and desire to eat 4.2.3.1. Baseline ratings. There was a significant main effect of time for pre-recall rated hunger F(1, 37)= 17.7, p b 0.01. As expected, rated hunger was greater 3-hours post-lunch compared with 1-hour post-lunch (mean hunger rating 1-hour post-lunch= 32.6, SEM = 3.6; mean hunger rating 3-hours post-lunch= 54.6, SEM = 3.2). There were no significant main effects of condition or disinhibition and no significant interactions (all p N 0.05). However, there was a significant effect of restraint on rated hunger whereby the restrained participants rated themselves as more hungry than the unrestrained participants, F(1, 37)= 4.1, p b 0.05 (mean hunger rating restrained = 38.2, SEM = 4.2; mean hunger rating unrestrained = 49, SEM = 3.1). For pre-recall rated fullness, there was a significant main effect of time, F(1, 38) = 17.6, p b 0.01: fullness ratings were lower 3-hours post-lunch compared with 1-hour post-lunch (mean fullness rating 1-hour post-lunch= 55.9, SEM = 4.1; mean fullness rating 3-hours post-lunch= 39.7, SEM= 3.4), but there were no other significant main effects of interactions (all p N 0.05). Finally, pre-recall rated desire to eat was significantly higher 3-hours post-lunch compared with 1-hour post-lunch, F(1, 38) = 12, p b 0.01 (mean desire to eat rating 1-hour post-lunch= 35.4, SEM = 4; mean desire to eat rating 3-hours post-lunch= 52.6, SEM = 3.7). 4.2.3.2. Pre- to post-recall changes. There were no significant effects of time, disinhibition or restraint on pre- to post-recall changes in rated hunger or fullness. For desire to eat ratings only, there was a significant interaction between condition and time and disinhibition, F(1, 38) = 5.6, p b 0.05, which was due to there being a greater reduction in desire to eat ratings for participants with a tendency toward disinhibition after journey recall at 3-hours post-lunch compared with 1-hour post-lunch.

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4.2.4. Cookie intake Analysis of cookie intake on the introductory day revealed that the groups did not differ in terms of their baseline intake, F(1, 38) = 0.06, p N 0.05 (mean cookie intake for the Lunch Today condition = 32 g; mean cookie intake for the Journey condition = 34 g), nor were there any significant interactions between condition and restraint and condition and disinhibition at baseline. For the test sessions, there was a significant main effect time, F(1, 76) = 17.7, p b 0.01, whereby cookie intake was greater in the 3-hour delay condition compared with the 1-hour delay condition. There were no main effects of cookie type, F(2, 76) = 1.0, p N 0.05, condition, F(1, 38) = 0.1, p N 0.05, restraint, F(1, 38) = 0.04, p N 0.05, or disinhibition F(1, 38) = 2.0, p N 0.5, on cookie intake and no significant interactions between condition, restraint and disinhibition. However, there was a significant interaction between condition, time and disinhibition, F(1, 76) = 5.2, p b 0.05. Post-hoc analysis showed that this interaction was accounted for by a reduction in intake of cookies by low disinhibition not high disinhibition participants in the Lunch Today condition at the 3-hours post-lunch test time only (marginally significant condition × time interaction for low disinhibition participants only) (Fig. 3). Further post-hoc analysis showed that this effect was accounted for by a reduction in consumption of hobnob cookies in the Lunch Today condition (p b 0.05). 4.2.5. Cookie preference and rated pleasantness Analysis of the cookie preference ratings showed that participants rated the digestive cookies as less pleasant in taste than either the crinkle crunch or the hobnobs, but that all of the cookies were rated as pleasant tasting (mean pleasantness rating for the digestives = 55,

Fig. 3. Intake of cookies at 1-hour post-lunch and 3-hours post-lunch as a function of condition for A) low disinhibition (N = 30) and B) high disinhibition participants (N = 16) in Experiment 3. Data are shown as mean intake (g) + SEM.

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SEM = 5.5; mean pleasantness rating for crinkle crunch = 64, SEM 3.3; mean pleasantness rating for hobnobs = 66, SEM = 2.5). There was no effect on condition or time on cookie ratings (all p N 0.05). A similar pattern of results was found for the rating of how often participants would choose the cookies, although the effect of biscuit type was not significant (p = 0.1) (mean choice rating for the digestives = 48.8, SEM = 4.1; mean choice rating for crinkle crunch = 58.1, SEM 4.5; mean choice rating for hobnobs = 59, SEM = 3.4). In this experiment, we found an effect of lunch recall on subsequent snack intake for participants scoring low in tendency toward disinhibition, thus replicating the finding from Experiment 2. We further found that the effect of recall on snack intake was dependent upon the time that had elapsed between lunch and the recall session. Snack intake was decreased significantly after recall in the 3-hour delay condition, but not the 1-hour delay condition. It is unlikely that floor effects can account for the lack of effect of recall on intake at 1-hour post-lunch in participants scoring low in tendency toward disinhibition. The minimum the participants would be expected to consume to make the ratings would equate to the average weight of each portion of biscuit provided, which was about 3–4 g (a quarter of a biscuit), but in the meal recall condition participants were eating on average 10 g of biscuit. Rather, the delay-dependency of the effect suggests that it is dependent on memory of the most recent meal rather than some non-memory related effect of the recall procedure. 5. General discussion We found that asking participants to recall lunch eaten that day decreased afternoon snack intake compared with recall of lunch eaten the previous day and recall of non-food-related information and that the effect was observed regardless of the type of snack consumed (popcorn versus cookies) and the palatability of the snack. These data suggest that the effect of meal recall is not mediated via changes in hedonic responding and is not specific to consuming high energy foods. We also found that meal recall was only effective in reducing snack intake if participants scored low and not high on a measure of tendency toward dietary disinhibition (Experiments 2 and 3). Although speculative, it may be that memory impairments interfere with the encoding of meal-related information in individuals who have a tendency towards disinhibited eating. We have further shown that the effect of recent meal recall is delay-dependent and therefore is likely to rely on memory, because snack intake was only reduced when testing took place 3-hours post-lunch and not after a 1-hour lunch-test interval (Experiment 3). The present results are also important in confirming that demand characteristics cannot explain the effects of recent meal recall on subsequent snack intake. None of the participants second-guessed the purpose of the studies and all were unaware of the hypotheses under test. We also found that the effect was not specific to recall or intake of particular foods, such as high energy foods, because it was observed when the participants ate a sandwich lunch in laboratory (Experiment 3) or ate a self-determined lunch (Experiments 1 and 2) and when the snack was low energy (popcorn) and higher energy (cookies). Finally, baseline differences in food intake were controlled for either by using a repeated-measures design (Experiment 1) or by taking baseline food intake into account in the analyses (Experiments 2 and 3). The results do not elucidate how recalling recent eating affects subsequent intake. It is possible that participants eat less when reminded of a recent meal because they consider it appropriate to eat less given the recent meal [12]. It is possible that changes in appetite satiety are cognitively mediated and depend upon the conjunction in memory of representations of food-related sensory cues, information about the previous post-ingestive consequences of consuming that

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food, current internal state cues, and the likely post-ingestive effects of recently consumed food. In support, internal state-dependent reductions in food intake in the presence of a sensory cue previously paired with the mildly aversive consequences of ingesting concentrated carbohydrate have been demonstrated in both people and rats [37,38] suggesting that such learned satiety has a role to play in the control of normal meal size [39]. Although we found no consistent effects of meal recall on rated appetite, we did not assess appetite ratings during the snack tasting so we do not know whether the momentary disposition to consume the snacks in the presence of sensory/visceral stimulation provided by those snacks was affected by prior meal recall. A final possibility is that information about recent eating is necessary for the interpretation of interoceptive cues associated with the consumption of food. From the work of Schachter, it is known that manipulation of cognitive and situational variables can affect a person's labelling of states of physiological arousal and consequent behavior [40]. It may be that thinking about recent eating facilitates the labelling of internal states associated with the consumption of food. In conclusion, the present results confirm that recalling a recent eating episode before consuming a snack can decrease intake of that snack. The results also suggest that this effect is likely to be related to memory of that episode. However, high scores on a measure of tendency toward dietary disinhibition are associated with a lack of effect of meal recall on snack intake and the possibility that this is due to impaired meal encoding/retrieval should be tested. Finally, the results imply that variations in the ability to remember recent eating episodes may contribute to individual differences in short-term food intake. Acknowledgement This work was supported by the Biotechnology and Biological Sciences Research Council (BBSRC); grant reference: D17871. References [1] Bellisle F, Dalix AM. Cognitive restraint can be offset by distraction, leading to increased meal intake in women. Am J Clin Nutr 2001;74:197–200. [2] Bellisle F, Dalix AM, Slama G. Non food-related environmental stimuli induce increased meal intake in healthy women: comparison of television viewing versus listening to a recorded story in laboratory settings. Appetite 2004;43:175–80. [3] Hetherington MM, Foster R, Anderson AS, Norton GNM. Understanding variety: tasting different foods delays satiation. Physiol Behav 2006;87:263–71. [4] Schachter S, Gross LP. Manipulated time and eating behaviour. J Pers Soc Psychol 1968;10(98):106. [5] Wooley SC. Physiologic versus cognitive factors in short term food regulation in the obese and non obese. Psychosom Med 1972;34:62–8. [6] Pliner P, Zec D. Meal schemas during a preload decrease subsequent eating. Appetite 2007;48:278–88. [7] de Castro JM. Social facilitation of duration and size but not rate of the spontaneous meal intake of humans. Physiol Behav 1990;47:1129–35. [8] de Castro JM. Family and friends produce greater social facilitation of food intake than other companions. Physiol Behav 1994;56:445–55. [9] Roth DA, Herman CP, Polivy J, Pliner P. Self-presentational conflict in social eating situations: a normative perspective. Appetite 2001;36:165–71. [10] Herman CP, Roth DA, Polivy J. Effects of the presence of others on food intake: a normative interpretation. Psychol Bull 2003;129:873–86.

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