Increased familiarity with eating a food to fullness underlies increased expected satiety

Expected satiety informs self-selected portion sizes and thereby influences energy intake. At present the extent to which these beliefs are learned remains unclear. In an initial study the proposition that familiarity influences expected satiety was explored. Self-report measures of familiarity, along with other measures such as degree of liking, were collected for wine gums and milk chocolate, together with expected satiety estimates obtained using a psychophysical task. Familiarity was indeed significantly correlated with expected satiety, but only in respect of frequency of having eaten the food to fullness. In a second experiment a significant increase in expected satiety was observed after eating a large portion of wine gums at a subsequent test session. Together, these findings indicate that expected satiety changes in response to increased familiarity of eating a food to satiety.

Children's familiarity with snack foods changes expectations about fullness

BACKGROUND

Palatability is regarded as a major determinant of children's energy intake. However, few studies have considered nonhedonic beliefs about foods. In adults, there is emerging evidence that expectations about the satiating properties of foods are an important determinant of meal size, and these beliefs are learned.

OBJECTIVE

We measured and quantified children's expected satiation across energy-dense snack foods by using a method of adjustment. Participants changed a comparison-food portion (pasta and tomato sauce) to match the satiation that they expected from a snack food. We predicted that children who were especially familiar with snack foods would expect the foods to generate greater satiation and that children who were unfamiliar with snack foods would match expected satiation on the basis of the physical characteristics (perceived volume) of the foods.

DESIGN

Seventy 11- to 12-y-old children completed measures of expected satiation, perceived volume, familiarity, and liking across 6 snack foods.

RESULTS

As anticipated, familiarity and expected satiation were positively related (r = 0.37, P = 0.002), and this association remained after liking was controlled for. Furthermore, expected-satiation and perceived-volume judgments were more dissimilar as familiarity with the foods increased.

CONCLUSIONS

Our findings highlight the role of learning in shaping children's beliefs about the postingestive effects of the consumption of foods; children who ate the foods more often expected them to deliver greater satiation. Furthermore, our findings suggest that, in the absence of prior experience, children rely on a food's physical characteristics (a less-complex strategy) when they judge expected satiation. This trial was registered at clinicaltrials.gov as NCT01403753.

Using a novel computer-based approach to assess the acute effects of exercise on appetite-related measures

Measuring food intake using standard buffet meals can be complicated by sensory and external cues which can alter energy intake. The present study was designed to examine the effects of acute exercise on non-metabolic factors related to appetite and food intake using a computer-based assessment. Twenty-seven men and women participated in two sessions in random order: 60-min walking on the treadmill (exercise trial; EX) or seated rest (control trial; CON). Subjective hunger and fullness, food liking, food utility, and ideal portion size were assessed before and immediately after exercise or rest, and hourly for 2 h. The findings showed that an acute bout of moderate intensity exercise had an anorexigenic effect; characterised by diminished hunger (-17.4%, p=0.004) and lower prospective ideal portion size (-7.7%, p=0.003) compared to no exercise. This novel, computer-based assessment, is a useful alternative to buffet meals setting and allows for the determination of non-metabolic factors associated with feeding behaviour in relation to exercise.

Playing a computer game during lunch affects fullness, memory for lunch, and later snack intake

BACKGROUND

The presence of distracting stimuli during eating increases the meal size and could thereby contribute to overeating and obesity. However, the effects of within-meal distraction on later food intake are less clear.

OBJECTIVE

We sought to test the hypothesis that distraction inhibits memory encoding for a meal, which, in turn, increases later food intake.

DESIGN

The current study assessed the effects of playing solitaire (a computerized card-sorting game) during a fixed lunch, which was eaten at a fixed rate, on memory for lunch and food intake in a taste test 30 min later. A between-subjects design was used with 44 participants. Participants in the no-distraction group ate the same lunch in the absence of any distracting stimuli.

RESULTS

Distracted individuals were less full after lunch, and they ate significantly more biscuits in the taste test than did nondistracted participants (mean intake: 52.1 compared with 27.1 g; P = 0.017). Furthermore, serial-order memory for the presentation of the 9 lunch items was less accurate in participants who had been distracted during lunch.

CONCLUSIONS

These findings provide further evidence that distraction during one meal has the capacity to influence subsequent eating. They may also help to explain the well-documented association between sedentary screen-time activities and overweight.

What determines real-world meal size? Evidence for pre-meal planning

The customary approach to the study of meal size suggests that 'events' occurring during a meal lead to its termination. Recent research, however, suggests that a number of decisions are made before eating commences that may affect meal size. The present study sought to address three key research questions around meal size: the extent to which plate-cleaning occurs; prevalence of pre-meal planning and its influence on meal size; and the effect of within-meal experiences, notably the development of satiation. To address these, a large-cohort internet-based questionnaire was developed. Results showed that plate-cleaning occurred at 91% of meals, and was planned from the outset in 92% of these cases. A significant relationship between plate-cleaning and meal planning was observed. Pre-meal plans were resistant to modification over the course of the meal: only 18% of participants reported consumption that deviated from expected. By contrast, 28% reported continuing eating beyond satiation, and 57% stated that they could have eaten more at the end of the meal. Logistic regression confirmed pre-meal planning as the most important predictor of consumption. Together, our findings demonstrate the importance of meal planning as a key determinant of meal size and energy intake.

'Expected satiety' changes hunger and fullness in the inter-meal interval

Previously, we have shown that foods differ markedly in the satiety that they are expected to confer (compared calorie-for-calorie). In the present study we tested the hypothesis that 'expected satiety' plays a causal role in the satiety that is experienced after a food has been consumed. Before lunch, participants (N=32) were shown the ingredients of a fruit smoothie. Half were shown a small portion of fruit and half were shown a large portion. Participants then assessed the expected satiety of the smoothie and provided appetite ratings, before, and for three hours after its consumption. As anticipated, expected satiety was significantly higher in the 'large portion' condition. Moreover, and consistent with our hypothesis, participants reported significantly less hunger and significantly greater fullness in the large-portion condition. Importantly, this effect endured throughout the test period (for three hours). Together, these findings confirm previous reports indicating that beliefs and expectations can have marked effects on satiety and they show that this effect can persist well into the inter-meal interval. Potential explanations are discussed, including the prospect that satiety is moderated by memories of expected satiety that are encoded around the time that a meal is consumed.

Cognitive biases to healthy and unhealthy food words predict change in BMI

The current study explored the predictive value of cognitive biases to food cues (assessed by emotional Stroop and dot probe tasks) on weight change over a 1-year period. This was a longitudinal study with undergraduate students (N = 102) living in shared student accommodation. After controlling for the effects of variables associated with weight (e.g., physical activity, stress, restrained eating, external eating, and emotional eating), no effects of cognitive bias were found with the dot probe. However, for the emotional Stroop, cognitive bias to unhealthy foods predicted an increase in BMI whereas cognitive bias to healthy foods was associated with a decrease in BMI. Results parallel findings in substance abuse research; cognitive biases appear to predict behavior change. Accordingly, future research should consider strategies for attentional retraining, encouraging individuals to reorient attention away from unhealthy eating cues.

The role of sensitivity to reward and impulsivity in food-cue reactivity

Exposure to the visual and olfactory characteristics of food can elicit a desire to eat and can stimulate food intake. This study sought to determine the extent to which sensitivity to reward and impulsivity are associated with this 'food-cue reactivity' in two motivational states (food deprived and non-food deprived). Female participants (N=120) were exposed to a pizza cue for three minutes whilst food deprived and non-food deprived. Before and after this period, three measures of food-cue reactivity were taken (ratings of desire to eat, craving, and desired portion size of the cued food). Two important findings emerged from the study. Firstly, individuals with higher levels of trait impulsivity experienced greater changes in appetite ratings in both motivational states (food deprived and non-food deprived). They also reported greater changes in desired portion size of a cued food when food deprived. Secondly, individuals with a high sensitivity to reward experienced a greater change in their desired portion of the cued food, but only when non-food deprived. These results indicate that individual differences in food-cue reactivity could be related to variation in sensitivity to stimuli that predict the occurrence of a reward, and to an inability to exercise sufficient self control in the presence of tempting environmental stimuli.

Effects of repeated exposure on liking for a reduced-energy-dense food

BACKGROUND

Reduced-energy-dense diet foods are often formulated to match the sensory characteristics of their regular-energy-dense counterparts. However, the extent to which attitudes toward a reduced-energy-dense food remain constant, even after repeated ingestion, remains to be explored systematically.

OBJECTIVE

The objective was to determine whether liking, "expected satiety," and "expected satiation" change after repeated exposure to a familiar food that has been reduced in energy density. Expected satiety and expected satiation refer to the extent to which foods are expected to stave off hunger and to deliver "fullness," respectively, when compared on a calorie-for-calorie basis.

DESIGN

Participants (n = 36) consumed either reduced-energy-dense (374 kcal) or standard-energy-dense (567 kcal) spaghetti Bolognese for lunch over 5 test sessions. During each test session, liking for the spaghetti Bolognese was assessed, together with measures of expected satiety and expected satiation.

RESULTS

Participants in the reduced-energy-dense condition reported a decrease in liking for the spaghetti Bolognese over the test sessions ( approximately 30%), whereas liking in the standard condition remained constant [condition (reduced/standard) x session (1-5) interaction, P < 0.008]. By contrast, both expected satiation and expected satiety remained similar across conditions and test sessions.

CONCLUSIONS

Over time, the pleasantness of a reformulated low-energy-dense food can decrease, and this may undermine its efficacy as a weight-loss product. It remains to be determined whether a longer period of "flavor-nutrient learning" is needed for shifts in expected satiety and expected satiation to be observed.

Familiarity changes expectations about fullness

Expected satiation (the extent to which a food is expected to deliver fullness) is an excellent predictor of self-selected portion size (kcal). Here, we explored the prospect that expected satiation changes over time. Fifty-eight participants evaluated expected satiation in eight test foods (including two 'candidate' foods: sushi and muesli) and reported how often they consumed each food. In one of the candidate foods (sushi), and across other test foods, expected satiation increased with familiarity. Together, these findings are considered in the context of 'satiation drift' - the hypothesis that foods are expected to deliver poor satiation until experience teaches us otherwise.

How many calories are on our plate? Expected fullness, not liking, determines meal-size selection

The availability of highly palatable food is thought to stimulate the selection of larger meals (leading to weight gain and obesity). In this article, we explore aspects of this proposition. Specifically, we scrutinize two basic assumptions: (i) palatable energy-dense foods are more rewarding (desired), and (ii) these palatable foods are selected in relatively larger portions. In combination with palatability, we also consider the relative role for "expected satiation"-the extent to which a food is expected to deliver satiation. A total of 17 commonly consumed foods were assessed by 28 normal-weight participants at lunchtime. Critically, our measure of food reward and expected satiation involves comparisons between foods based on equicaloric portions. When assessed in this way, we find that food reward and ideal portion sizes (in kcal) are both closely associated with expected satiation, but not with "expected liking." Low expected satiation (not expected liking) predicts the selection of large portion sizes (in kcal) and foods with this characteristic tend to be more energy dense and are regarded as less (not more) rewarding (when compared calorie for calorie). Together, these findings challenge the role of palatability in meal-size selection and they highlight the importance of expected satiation, a "nonaffective" component of food reward.

Flavour-flavour learning occurs automatically and only in hungry participants

A novel flavour may become liked if it is presented repeatedly and in combination with a second flavour that is already liked. Conceptually, this 'flavour-flavour learning' is important, because it can account for many of our everyday food and flavour preferences. However, relatively little is known about the underlying process because learning paradigms have lacked reliability. Based on previous research we explored whether learning is determined by three variables; i) hunger state, ii) demand and contingency awareness, and iii) dietary restraint. Participants (male n=15/female n=15) consumed three different and novel-tasting fruit teas. One of the teas had a non-caloric sweetener added (CS+) and two were unsweetened (CS-). Before and after this training the participants ranked their preference for unsweetened versions of the three teas. We found that the training increased preference for the CS+ relative to the CS- teas. However, this effect was only found in hungry participants. We also found little evidence that learning was related to whether the participants could identify (recognition test) the specific tea that had been sweetened during training, suggesting that the underlying process is automatic and it operates outside conscious awareness. Learning was not predicted by dietary restraint (measured using the DEBQ-R scale). Together, these findings provide further evidence for a linkage between flavour-flavour learning and flavour-nutrient learning.

Associative learning and the control of human dietary behavior

Most of our food likes and disliked are learned. Relevant forms of associative learning have been identified in animals. However, observations of the same associative processes are relatively scarce in humans. The first section of this paper outlines reasons why this might be the case. Emphasis is placed on recent research exploring individual differences and the importance or otherwise of hunger and contingency awareness. The second section briefly considers the effect of learning on meal size, and the author revisits the question of how learned associations might come to influence energy intake in humans.

Flavor-nutrient learning in restrained and unrestrained eaters

After we consume a novel food an association can form between its sensory characteristics (e.g., taste properties) and the effect it has on the body (rewarding). Associations of this kind underpin much of our everyday dietary behavior because they mediate both the affective quality of food (flavor-preference learning) and the amount that we choose to consume (learning satiation). Notwithstanding this fact, very few studies have successfully demonstrated the process of dietary learning in human adults. In addition, based on evidence from related research, we explored whether learning is less likely to occur in individuals who have high scores on a measure of dietary restraint. Female participants (N = 44) consumed two differently flavored desserts. Each was presented three times on separate days. One was formulated with a high-energy content (1882 kJ) and the other with a low-energy content (226 kJ). After training, we found little evidence for learned satiation. However, we did observe flavor-preference learning. Specifically, participants acquired a greater liking and desire-to-eat the dessert flavor that was paired with a higher energy density during training. Further analysis revealed that this effect on liking is qualified by dietary restraint. As predicted, unrestrained eaters demonstrated greater differential responding to the two desserts than did restrained eaters. These data provide further evidence for flavor-nutrient learning in adults and they highlight a hitherto unexplored and potentially important difference between restrained and unrestrained eaters.

Effects of distraction on the development of satiety

Two experiments explored the hypothesis that distraction causes a reduced sensitivity to the physiological and sensory cues that signal when to terminate a meal. In Experiment 1, eighty-eight females ate five 'Jaffa Cakes' either while distracted by a computer game or while sitting in silence. Analysis of the difference in rated hunger, fullness and desire to eat (pre- to post-intake) revealed that distracted participants experienced smaller changes in their desire to eat and fullness than did non-distracted participants. Experiment 2 assessed whether changes in ratings are attenuated because sensory-specific satiety (or a related process) fails to develop. Using a similar procedure, eighty-four females provided desire to eat, pleasantness and intensity ratings for Jaffa Cakes and for two 'uneaten' foods, both before and at three time-points after consuming five Jaffa Cakes. Non-distracted participants reported a reduction in their desire to eat the eaten food relative to the uneaten food (food-specific satiety), whereas distracted participants maintained a desire to eat all foods. Moreover, this difference between distracted and non-distracted participants was evident 5 and 10 min after the eating episode had terminated. The present findings invite speculation that distraction attenuates the development of sensory-specific satiety, and that this effect persists (at least for a brief period) after the distractor has terminated. More generally, this kind of phenomenon warrants further scrutiny because it holds the potential to contribute towards overeating, either by prolonging an eating episode or by reducing the interval between meals.

Everyday dietary behaviour and the relationship between attention and meal size

Previously, it has been demonstrated that overeating can occur when an individual engages in a cognitive task during a meal. One possibility, therefore, is that task performance can provide a measure of attention to dietary control. To explore this idea we measured performance on an otherwise irrelevant task during a meal. In two experiments, we compared intake and performance across five groups of females; dieters, and four groups of non-dieters, each with contrasting high and low scores on the restraint scale of the Dutch Eating Behaviour Questionnaire and the disinhibition scale of the Three-Factor Eating Questionnaire. Our analysis suggests that a correspondence can exist between task performance and intake (Experiment 1) and this might be influenced by the extent to which foods are regarded as forbidden (Experiment 2). However, aspects of our data are difficult to reconcile with the idea that task performance reflects a simple measure of attention to dietary control. Instead, one possibility is that individuals differ in the way that they choose to allocate attention during a meal. In relation to this idea, we discuss the possibility that some individuals choose to avoid food-related cognition by engaging strategically with other aspects of their cognitive environment.

Dietary restraint and US devaluation predict evaluative learning

Previous research has indicated that flavor-flavor learning is impaired in restrained eaters. In Experiment 1 we sought to extend this finding using a larger sample and a more comprehensive assessment of dietary behavior. Participants (N=90, including 30 current dieters) sampled three novel flavors (CSs), each on 10 separate occasions, in a randomized order. Each flavor was paired with chocolate (US) either 10%, 50%, or 90% of the time. We then assessed liking for the three CSs and asked participants to complete the DEBQ-restraint and TFEQ-disinhibition sub-scales. After these CS-US parings, restrained eaters tended to prefer the 10% paired flavor whereas unrestrained eaters tended to prefer the 90% paired flavor. Differential CS liking was not evident in dieters and it was not predicted by disinhibition. Using a similar methodology, in Experiment 2 (N=76) we assessed evaluative change following picture-sweet pairings. Relative to the other CSs, the restrained eaters reported a greater increase in their liking for the 10% paired CS and the unrestrained eaters reported a greater increase in their liking for the 90% paired CS. We also discovered that evaluative change is related to the level of US devaluation that takes place during conditioning. Evidence that a sweet US can bring about a decrease in liking has not been reported previously. One interpretation is that negative beliefs and attitudes can contaminate the representation of the US during training.

Dietary restraint and cognitive performance in children

Adults who attempt to restrict their dietary intake also tend to perform worse on a range of cognitive tasks. However, the extent to which this finding generalises to children has remained unclear. Following studies involving adults, we asked 44 girls (mean age = 10.1 years) to complete a simple reaction-time task and the Tower of London task. This group was selected from a local community school in the East Midlands (UK). Dietary restraint was measured using a version of the Dutch Eating Behaviour Questionnaire that had been adapted for use by children. Our results indicate that children with high restraint scores have longer reaction times and they also tend to perform worse on the TOL task. Other aspects of our data also suggest the dietary restraint may be correlated negatively with a measure of academic ability. We discuss reasons why restraint and performance might be related causally and we conclude that this issue warrants further scrutiny.