Jeffrey Michael Brunstrom

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.

‘I just can’t help myself’: effects of food-cue exposure in overweight and lean individuals

Objective:Even brief exposure to the sight and smell of food has been shown to increase reported appetite, initiate ‘cephalic phase responses,’ and increase planned and actual consumption. This experiment tested the hypothesis that overweight individuals are especially sensitive to these established effects of food-cue exposure.Design:Overweight (n=52) and normal-weight (n=52) participants were exposed to the sight and smell of a ‘cued’ food (pizza) for 60 s. Before and after this period, we assessed salivation, prospective (planned) portion size, and desire to eat pizza and other ‘non-cued’ foods. Participants were then offered ad libitum access to pizza.Results:Consistent with previous studies, food-cue exposure increased rated hunger and desire to eat, increased prospective portion size of all savory foods, and increased salivation. In overweight individuals, cue exposure (i) elicited a significantly greater salivary response and, (ii) evoked a significantly greater increase in desire to eat both the cued food and another non-cued food.Conclusion:After cue exposure, overweight individuals experience a greater motivation to consume food but do not desire or consume greater amounts of food. These findings are consistent with evidence that snacking and meal variability predict weight gain and they expose ‘cue reactiveness’ as a potential predisposing factor for overweight.

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.

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.

Computer-based assessments of expected satiety predict behavioural measures of portion-size selection and food intake ☆

Previously, expected satiety (ES) has been measured using software and two-dimensional pictures presented on a computer screen. In this context, ES is an excellent predictor of self-selected portions, when quantified using similar images and similar software. In the present study we sought to establish the veracity of ES as a predictor of behaviours associated with real foods. Participants (N=30) used computer software to assess their ES and ideal portion of three familiar foods. A real bowl of one food (pasta and sauce) was then presented and participants self-selected an ideal portion size. They then consumed the portion ad libitum. Additional measures of appetite, expected and actual liking, novelty, and reward, were also taken. Importantly, our screen-based measures of expected satiety and ideal portion size were both significantly related to intake (p<.05). By contrast, measures of liking were relatively poor predictors (p>.05). In addition, consistent with previous studies, the majority (90%) of participants engaged in plate cleaning. Of these, 29.6% consumed more when prompted by the experimenter. Together, these findings further validate the use of screen-based measures to explore determinants of portion-size selection and energy intake in humans.

Acute sleep deprivation increases portion size and affects food choice in young men

Acute sleep loss increases food intake in adults. However, little is known about the influence of acute sleep loss on portion size choice, and whether this depends on both hunger state and the type of food (snack or meal item) offered to an individual. The aim of the current study was to compare portion size choice after a night of sleep and a period of nocturnal wakefulness (a condition experienced by night-shift workers, e.g. physicians and nurses). Sixteen men (age: 23 ± 0.9 years, BMI: 23.6 ± 0.6 kg/m(2)) participated in a randomized within-subject design with two conditions, 8-h of sleep and total sleep deprivation (TSD). In the morning following sleep interventions, portion size, comprising meal and snack items, was measured using a computer-based task, in both fasted and sated state. In addition, hunger as well as plasma levels of ghrelin were measured. In the morning after TSD, subjects had increased plasma ghrelin levels (13%, p=0.04), and chose larger portions (14%, p=0.02), irrespective of the type of food, as compared to the sleep condition. Self-reported hunger was also enhanced (p<0.01). Following breakfast, sleep-deprived subjects chose larger portions of snacks (16%, p=0.02), whereas the selection of meal items did not differ between the sleep interventions (6%, p=0.13). Our results suggest that overeating in the morning after sleep loss is driven by both homeostatic and hedonic factors. Further, they show that portion size choice after sleep loss depend on both an individuals hunger status, and the type of food offered.

Subtle changes in the flavour and texture of a drink enhance expectations of satiety

BackgroundThe consumption of liquid calories has been implicated in the development of obesity and weight gain. Energy-containing drinks are often reported to have a weak satiety value: one explanation for this is that because of their fluid texture they are not expected to have much nutritional value. It is important to consider what features of these drinks can be manipulated to enhance their expected satiety value. Two studies investigated the perception of subtle changes in a drink’s viscosity, and the extent to which thick texture and creamy flavour contribute to the generation of satiety expectations. Participants in the first study rated the sensory characteristics of 16 fruit yogurt drinks of increasing viscosity. In study two, a new set of participants evaluated eight versions of the fruit yogurt drink, which varied in thick texture, creamy flavour and energy content, for sensory and hedonic characteristics and satiety expectations.ResultsIn study one, participants were able to perceive small changes in drink viscosity that were strongly related to the actual viscosity of the drinks. In study two, the thick versions of the drink were expected to be more filling and have a greater expected satiety value, independent of the drink’s actual energy content. A creamy flavour enhanced the extent to which the drink was expected to be filling, but did not affect its expected satiety.ConclusionsThese results indicate that subtle manipulations of texture and creamy flavour can increase expectations that a fruit yogurt drink will be filling and suppress hunger, irrespective of the drink’s energy content. A thicker texture enhanced expectations of satiety to a greater extent than a creamier flavour, and may be one way to improve the anticipated satiating value of energy-containing beverages.

Episodic Memory and Appetite Regulation in Humans

Psychological and neurobiological evidence implicates hippocampal-dependent memory processes in the control of hunger and food intake. In humans, these have been revealed in the hyperphagia that is associated with amnesia. However, it remains unclear whether ‘memory for recent eating’ plays a significant role in neurologically intact humans. In this study we isolated the extent to which memory for a recently consumed meal influences hunger and fullness over a three-hour period. Before lunch, half of our volunteers were shown 300 ml of soup and half were shown 500 ml. Orthogonal to this, half consumed 300 ml and half consumed 500 ml. This process yielded four separate groups (25 volunteers in each). Independent manipulation of the ‘actual’ and ‘perceived’ soup portion was achieved using a computer-controlled peristaltic pump. This was designed to either refill or draw soup from a soup bowl in a covert manner. Immediately after lunch, self-reported hunger was influenced by the actual and not the perceived amount of soup consumed. However, two and three hours after meal termination this pattern was reversed - hunger was predicted by the perceived amount and not the actual amount. Participants who thought they had consumed the larger 500-ml portion reported significantly less hunger. This was also associated with an increase in the ‘expected satiation’ of the soup 24-hours later. For the first time, this manipulation exposes the independent and important contribution of memory processes to satiety. Opportunities exist to capitalise on this finding to reduce energy intake in humans.

Individual differences in food-cue reactivity. The role of BMI and everyday portion-size selections.

This study sought to explore the association between sensitivity to food cues (sight and smell of food) and (i) body weight (overweight or non-overweight), (ii) typical everyday portion sizes, and (iii) the DEBQ-restraint scale. One hundred and twenty female participants (aged between 18 and 30) were exposed to the sight and smell of pizza for three minutes. Both before and after this period, three measures of food-cue reactivity were taken (ratings of desire to eat, craving, and a measure of desired portion size of the cued food). Separate regression analyses were used to explore the associations between the change in measures of cue reactivity from pre- to post-cue exposure, and (i) an overweight/non-overweight classification, (ii) a measure of participants everyday portion-size selection, and (iii) scores on the DEBQ-restraint scale. This analysis revealed that scores on the DEBQ-restraint scale were not significantly associated with changes in food-cue reactivity. However, individuals identified as overweight, and participants who reported consuming the largest everyday portion sizes, experienced a significantly greater change in their desired portion size of the cued food. The findings suggest that heightened food-cue reactivity might present an under-explored risk factor for overeating, and becoming overweight, and/or maintaining an overweight body shape.

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.