Inhibitory control mediates the effect of high intensity interval exercise on food choice

Exercise is associated with changes in food consumption and cognitive function. The aim of this study was to examine the immediate effects of acute exercise on appetite, food choices, and cognitive processes, and the mediating role of cognitive functioning, namely inhibitory control, working memory, cognitive flexibility and decision making. We compared the effects of high-intensity interval exercise (HIIE) to a resting condition on appetite and food choices, using visual analogue rating scales and a computerised portion selection task. Mediation analysis was performed with exercise/rest condition as a predictor variable and cognitive measures were entered as mediating variables and food choice measures as outcomes. Young women with low activity levels, aged between 18-35 years with a body mass index (BMI) between 18-25 kg/m2, were recruited. Participants (n=30) demonstrated improved performance on a Stroop task following HIIE compared to the rest session, indicating enhanced attentional inhibition. Accuracy on an N-back task was significantly higher after HIIE, indicating an improvement in working memory and response times on the N-back task were shorter after HIIE, suggesting increased processing speed. Delay discounting for food (but not money) was reduced after HIEE but there were no significant on go/no-go task performance. On the trail-making task (a measure of cognitive flexibility), the time difference between trail B and A was significantly lower after HIIE, compared to rest. HIIE reduced rated enjoyment and ideal portion size selection for high energy dense foods. The relationship between exercise and food choices was mediated by inhibition as assessed by the Stoop task. These results suggest that HIIE leads to cognitive benefits and a reduced preference for high-calorie foods and that an enhancement of attentional inhibition may underlie this relationship.

Development of Momentary Appetite Capture (MAC): A versatile tool for monitoring appetite over long periods

Understanding how an intervention impacts appetite in real-life settings and over several days remains a challenging and under-explored research question. To this end, we developed Momentary Appetite Capture (MAC), a form of ecological momentary assessment that combines automated text messaging with an online platform. Participants report their appetite using visual analogue scales (hunger, desire to eat, and fullness) and a virtual portion-size selection task. In two separate studies, we assessed the feasibility and test-retest reliability of MAC. Participants were prompted every 2 hours over a 14-hour window, and they repeated this assessment over two consecutive weekdays. For each participant, we calculated a daily time-averaged area under the curve (AUC) for each appetite measure. In Study One (N = 25) time-averaged AUC was significantly positively correlated across test days for hunger (r = 0.563, p = .003), desire to eat (r = 0.515, p = .008) and prospective portion size (r = 0.914, p < .001), but not for fullness (r = 0.342, p = .094). Participants completed 95% of MACs (380 of 400), and we used participant feedback to improve the MAC tool and study protocol for Study Two. In Study Two (N = 31), 94% of MACs were completed (468 of 496). Across days, time-averaged AUC was significantly positively correlated for hunger (r = 0.595, p = < .001), fullness (r = 0.501, p = .004), desire to eat (r = 0.585, p < .001), and prospective portion size (r = 0.757, p < .001). Together, these studies suggest that MAC could be an acceptable and reliable tool to track appetite throughout the day. In the future, MAC could be used to explore the impact of weight-loss interventions on natural fluctuations in appetite.

Evidence that carbohydrate-to-fat ratio and taste, but not energy density or NOVA level of processing, are determinants of food liking and food reward

This virtual (online) study tested the common but largely untested assumptions that food energy density, level of processing (NOVA categories), and carbohydrate-to-fat (CF) ratio are key determinants of food reward. Individual participants (224 women and men, mean age 35 y, 53% with healthy weight, 43% with overweight or obesity) were randomised to one of three, within-subjects, study arms: energy density (32 foods), or level of processing (24 foods), or CF ratio (24 foods). They rated the foods for taste pleasantness (liking), desire to eat (food reward), and sweetness, saltiness, and flavour intensity (for analysis averaged as taste intensity). Against our hypotheses, there was not a positive relationship between liking or food reward and either energy density or level of processing. As hypothesised, foods combining more equal energy amounts of carbohydrate and fat (combo foods), and foods tasting more intense, scored higher on both liking and food reward. Further results were that CF ratio, taste intensity, and food fibre content (negatively), independent of energy density, accounted for 56% and 43% of the variance in liking and food reward, respectively. We interpret the results for CF ratio and fibre in terms of food energy-to-satiety ratio (ESR), where ESR for combo foods is high, and ESR for high-fibre foods is low. We suggest that the metric of ESR should be considered when designing future studies of effects of food composition on food reward, preference, and intake.

Further evidence for sensitivity to energy density and a two-component model of meal size: Analysis of meal calorie intakes in Argentina and Malaysia

Previously, we demonstrated a non-linear association between meal caloric intake and meal energy density (ED, kcal/g) in data from a controlled trial in the US and from free-living participants in the UK [1]. In both datasets, meal caloric intake increased with ED in lower energy-dense meals (below ∼1.75 kcal/g) and decreased in higher energy-dense meals (above ∼1.75 kcal/g). In the current study, we sought to explore whether this pattern extends to data from free-living participants in Argentina (N = 2738 meals) and Malaysia (N = 4658 meals). Again, a significant breakpoint was found in both the Argentinean (2.04 kcal/g (SE = 0.06)) and Malaysian (2.17 kcal/g (SE = 0.06)) datasets with mean centered meal caloric intake increasing with ED below the breakpoint and decreasing above the breakpoint. These results lend further support for our two-component theoretical model of meal size (g) in which a volume signal is dominant in lower energy-dense meals and a calorie-content signal is dominant in higher energy-dense meals. Together, our research adds to evidence supporting human sensitivity to calories and exposes a complexity in the correspondence between meal energy content and meal size in everyday (non-manipulated) meals. Further research is needed to provide causal evidence for this sensitivity and whether individual variation impacts meal size and energy balance.

The Effect of Intermittent Fasting on Appetite: A Systematic Review and Meta-Analysis

Previously, narrative reviews have considered the effects of intermittent fasting on appetite. One suggestion is that intermittent fasting attenuates an increase in appetite that typically accompanies weight loss. Here, we conducted the first systematic review and meta-analysis to quantify the effects of intermittent fasting on appetite, when compared to a continuous energy restriction intervention. Five electronic databases and trial registers were searched in February 2021 and February 2022. Abstracts (N = 2800) were screened and 17 randomized controlled trials (RCTs), consisting of a variety of intermittent fasting regimes, met our inclusion criteria. The total number of participants allocated to interventions was 1111 and all RCTs were judged as having either some concerns or a high risk of bias (Cochrane RoB 2.0 tool). Random effects meta-analyses were conducted on change-from-baseline appetite ratings. There was no clear evidence that intermittent fasting affected hunger (WMD = -3.03; 95% CI [-8.13, 2.08]; p = 0.25; N = 13), fullness (WMD = 3.11; 95% CI [-1.46, 7.69]; p = 0.18; N = 10), desire to eat (WMD = -3.89; 95% CI [-12.62, 4.83]; p = 0.38; N = 6), or prospective food consumption (WMD = -2.82; 95% CI [-3.87, 9.03]; p = 0.43; N = 5), differently to continuous energy restriction interventions. Our results suggest that intermittent fasting does not mitigate an increase in our drive to eat that is often associated with continuous energy restriction.

Human nutritional intelligence underestimated? Exposing sensitivities to food composition in everyday dietary decisions

The social and cultural significance of food is woven into every aspect of our dietary behaviour, and it contributes to our complex interaction with food. To find order within this complexity scientists often look for dietary 'universals' - phenomena or basic principles that guide our food choice and meal size, irrespective of wider context. One such idea is that taste characteristics provide a signal for dietary composition (e.g., sweet taste signals carbohydrate). Others have suggested that behaviour is guided by learning and is based on associations that form between the flavour of a food and its post-ingestive effects. Despite a large body of research, evidence supporting both processes is equivocal, leading some to conclude that humans are largely indifferent to food composition. Here, we argue that human abilities to gauge the nutritional composition or value of food have been underestimated, and that they can be exposed by embracing alternative methods, including cross-cultural comparisons, large nutrition surveys, and the use of virtual portion-selection tools. Our group has focused on assessments of food choice and expected satiety, and how comparisons across everyday foods can reveal non-linear relationships with food energy density, and even the potential for sensitivity to micronutrient composition. We suggest that these abilities might reflect a complex form of social learning, in which flavour-nutrient associations are not only formed but communicated and amplified across individuals in the form of a cuisine. Thus, rather than disregarding sociocultural influences as extraneous, we might reimagine their role as central to a process that creates and imbues a 'collective dietary wisdom.' In turn, this raises questions about whether rapid dietary, technological, and cultural change disrupts a fundamental process, such that it no longer guarantees a 'nutritional intelligence' that confers benefits for health.

Portion-control tableware differentially impacts eating behaviour in women with and without overweight

Portion control tableware has been described as a potentially effective approach for weight management, however the mechanisms by which these tools work remain unknown. We explored the processes by which a portion control (calibrated) plate with visual stimuli for starch, protein and vegetable amounts modulates food intake, satiety and meal eating behaviour. Sixty-five women (34 with overweight/obesity) participated in a counterbalanced cross-over trial in the laboratory, where they self-served and ate a hot meal including rice, meatballs and vegetables, once with a calibrated plate and once with a conventional (control) plate. A sub-sample of 31 women provided blood samples to measure the cephalic phase response to the meal. Effects of plate type were tested through linear mixed-effect models. Meal portion sizes (mean ± SD) were smaller for the calibrated compared with the control plate (served: 296 ± 69 vs 317 ± 78 g; consumed: 287 ± 71 vs 309 ± 79 g respectively), especially consumed rice (69 ± 24 vs 88 ± 30 g) (p < 0.05 for all comparisons). The calibrated plate significantly reduced bite size (3.4 ± 1.0 vs 3.7 ± 1.0 g; p < 0.01) in all women and eating rate (32.9 ± 9.5 vs 33.7 ± 9.2 g/min; p < 0.05), in lean women. Despite this, some women compensated for the reduced intake over the 8 h following the meal. Pancreatic polypeptide and ghrelin levels increased post-prandially with the calibrated plate but changes were not robust. Plate type had no influence on insulin, glucose levels, or memory for portion size. Meal size was reduced by a portion-control plate with visual stimuli for appropriate amounts of starch, protein and vegetables, potentially because of the reduced self-served portion size and the resulting reduced bite size. Sustained effects may require the continued use of the plate for long-term impact.

Development and validation of a new methodological platform to measure behavioral, cognitive, and physiological responses to food interventions in real time

To fully understand the causes and mechanisms involved in overeating and obesity, measures of both cognitive and physiological determinants of eating behavior need to be integrated. Effectively synchronizing behavioral measures such as meal micro-structure (e.g., eating speed), cognitive processing of sensory stimuli, and metabolic parameters, can be complex. However, this step is central to understanding the impact of food interventions on body weight. In this paper, we provide an overview of the existing gaps in eating behavior research and describe the development and validation of a new methodological platform to address some of these issues. As part of a controlled trial, 76 men and women self-served and consumed food from a buffet, using a portion-control plate with visual stimuli for appropriate amounts of main food groups, or a conventional plate, on two different days, in a random order. In both sessions participants completed behavioral and cognitive tests using a novel methodological platform that measured gaze movement (as a proxy for visual attention), eating rate and bite size, memory for portion sizes, subjective appetite and portion-size perceptions. In a sub-sample of women, hormonal secretion in response to the meal was also measured. The novel platform showed a significant improvement in meal micro-structure measures from published data (13 vs. 33% failure rate) and high comparability between an automated gaze mapping protocol vs. manual coding for eye-tracking studies involving an eating test (ICC between methods 0.85; 90% CI 0.74, 0.92). This trial was registered at Clinical Trials.gov with Identifier NCT03610776.

Time to revisit the passive overconsumption hypothesis? Humans show sensitivity to calories in energy-rich meals

BACKGROUND

A possible driver of obesity is insensitivity (passive overconsumption) to food energy density (ED, kcal/g); however, it is unclear whether this insensitivity applies to all meals.

OBJECTIVES

We assessed the influence of ED on energy intake (kcal) across a broad and continuous range of EDs comprised of noncovertly manipulated, real-world meals. We also allowed for the possibility that the association between energy intake and ED is nonlinear.

METHODS

We completed a secondary analysis of 1519 meals which occurred in a controlled environment as part of a study conducted by Hall and colleagues to assess the effects of food ultra-processing on energy intake. To establish the generalizability of the findings, the analyses were repeated in 32,162 meals collected from free-living humans using data from the UK National Diet and Nutrition Survey (NDNS). Segmented regressions were performed to establish ED "breakpoints" at which the association between consumed meal ED and mean centered meal caloric intake (kcal) changed.

RESULTS

Significant breakpoints were found in both the Hall et al. data set (1.41 kcal/g) and the NDNS data set (1.75 and 2.94 kcal/g). Centered meal caloric intake did not increase linearly with consumed meal ED, and this pattern was captured by a 2-component ("volume" and "calorie content" [biologically derived from the sensing of fat, carbohydrate, and protein]) model of physical meal size (g), in which volume is the dominant signal with lower energy-dense foods and calorie content is the dominant signal with higher energy-dense foods.

CONCLUSIONS

These analyses reveal that, on some level, humans are sensitive to the energy content of meals and adjust meal size to minimize the acute aversive effects of overconsumption. Future research should consider the relative importance of volume and calorie-content signals, and how individual differences impact everyday dietary behavior and energy balance.

Virtual reality exergaming improves affect during physical activity and reduces subsequent food consumption in inactive adults

An individual's affective (i.e. emotional) response to exercise may play an important role in post-exercise eating behaviour for some individuals. Taking advantage of advances in fully immersive virtual reality (VR) technology, this study aimed to: a) examine whether VR exergaming can improve the psychological response to exercise in inactive adults, and b) assess the extent to which this improvement reduces post-exercise appetite and eating behaviour. In a cross-over study, 34 adults not meeting the World Health Organisation's physical activity recommendations completed two exercise sessions on a stationary bike; one while engaging in a VR exergame and one without VR. Monitoring enabled heart rate, energy expenditure, and duration across conditions to be closely matched. The Physical Activity Enjoyment Scale, Feeling Scale, Felt Arousal Scale and Borg's Ratings of Perceived Exertion were measured to capture the affective responses to exercise. Appetite and eating behaviour were evaluated using visual-analogue scales, a computerised food preference task, and intake at a post-exercise buffet meal. Cycling in VR elicited greater exercise enjoyment (p < 0.001, η2p = 0.62), pleasure (p < 0.001, η2p = 0.47), and activation (p < 0.001, η2p = 0.55). VR exergaming did not alter perceived physical exertion (p = 0.64), perceived appetite (p = 0.68), and preference for energy dense (p = 0.78) or sweet/savoury foods (p = 0.90) compared to standard exercise. However, it did result in a mean 12% reduction in post-exercise food intake (mean difference: 105.9 kcal; p < 0.01; η2p = 0.20) and a decrease in relative food intake (p < 0.01; η2p = 0.20), although inter-individual differences in response to VR exergaming were observed. The integration of VR in a cycling workout improves the affective experience of physical activity for inactive adults and reduces subsequent food intake. Virtual reality technology shows potential as an adjunct tool to support adults in weight management programmes become more active, especially for those individuals who are prone to eat in excess after physical activity.

Current appetite influences relative differences in the expected satiety of foods for momentary, but not hypothetical, expected satiety assessments

Research has shown that expected satiety is highly associated with portion-size selection and can vary (kcal-for-kcal) significantly between foods. However, research has not adequately investigated whether current appetite influences relative differences in the expected satiety of foods. This is important to explore to better understand how current motivational state influences food choice and portion selection. This study used 'hypothetical' and 'momentary' expected-satiety assessments to understand whether methods requiring a reflection on current motivational state [momentary] versus more hypothetical considerations when assessing expected satiety can influence the interpretation of results. It was hypothesised that current appetite would only influence relative differences in expected satiety between foods for momentary, but not hypothetical, expected satiety assessments. Participants (n = 54) were shown images of twelve foods, once when hungry and once when full. In each case, they selected a portion for each food to 1) match the expected satiety of a fixed-portion 'standard' food [hypothetical], and 2) stave off hunger until their next meal [momentary]. Results showed that the relative between-food comparison of expected satiety was stable for hypothetical (p=.73) but not momentary assessments (p<.001) suggesting that while current motivational state may influence food choice and portion selection in the moment, more generalised comparisons of the satiating abilities of foods (learned over a longer period) remain stable. This is important 1) for methods in future studies, as immediate dietary intake does not appear to influence hypothetical expected satiety, thus dietary control is not necessary before participants undertake these assessments, and 2) as it confirms that difficulties associated with dietary regulation may not be due to inaccurate hypothetical judgements about foods, but instead appear to be influenced by contextual nuances that occur in the moment.

Social facilitation of energy intake in adult women is sustained over three days in a crossover laboratory experiment and is not compensated for under free-living conditions

People eat more when they eat a meal with familiar others than they do when eating alone. However, it is unknown whether eating socially impacts intake over the longer-term. The aim of Study 1 was to examine whether socially facilitated intake is sustained across all meals and across three consecutive days. The aim of Study 2 was to examine whether increased intake during a social meal taken in the laboratory is compensated for under free-living conditions. In Study 1, adult women (n = 26) ate all their meals across three days either with a friend or alone in a counterbalanced cross-over design. In Study 2 adult women (n = 63) consumed a meal in the laboratory either alone or with two friends and then recorded everything they ate and drank for the next three days using electronic food diary software. In Study 1 intake across 3 days was significantly greater in the Social (M = 7310 kcal, SD = 1114) than in the Alone condition (M = 6770 kcal, SD = 974) (F(1,423) = 16.10, p < .001, d = 0.51). In Study 2 participants consumed significantly more in the laboratory when eating with their friends (M = 1209 kcal, SD = 340) than when eating alone (M = 962 kcal, SD = 301) (F(1,63) = 13.28, p = .001, d = 0.77). Analysis of food diary data plus laboratory intake showed that intake remained significantly greater in the Social (M = 6396 kcal, SD = 1470) than in the Alone condition after 4 days (M = 5776 kcal, SD = 1182) (F(1,59) = 5.59, p = .021, d = 0.05). These results show that social facilitation of eating is sustained over three days and suggest that people fail to compensate for the social facilitation of eating.

Micronutrients and food choice: A case of 'nutritional wisdom' in humans?

Many reports show that non-human animals have the ability to select foods based on their micronutrient composition. However, it is unclear whether humans also have this ability, and we have lacked appropriate methods to investigate this question. In response to this challenge, we developed an approach that derives evidence from patterns of choices across a range of food images. In two studies (Study 1, N = 45; Study 2, N = 83) adults selected one of two pairs of fruits and vegetables in a series of trials (N = 210). Consistent with variety seeking, they preferred 'varied' over 'monotonous' pairs (same-food pairs were less attractive). However, and even after controlling for explicit nutritional knowledge (Study 2) and food energy density (Study 1 and 2), we observed a significant tendency to select pairings that offered: i) greater total micronutrient intake and ii) greater 'micronutrient complementarity' (MC), i.e., a broader range of micronutrients. In a separate analysis, a similar pattern was observed in two-component meals (e.g., steak and fries) drawn from a large national nutrition survey in the UK (1086 records). Specifically, the MC of these meals was greater than would be predicted by chance (p < .0001) and when a meal provided an excess of micronutrients (>100% daily recommended amount) then this occurred less often than by chance (p < .0001), i.e., 'micronutrient redundancy' was avoided. Together, this work provides new evidence that micronutrient composition influences food choice (a form of 'nutritional wisdom') and it raises questions about whether nutritional requirements are otherwise met through dietary 'variety seeking'. In turn, it also exposes the potential for a complexity in human dietary decision making that has not been recognised previously.

Multi-component food-items and eating behaviour: What do we know and what do we need to know?

Multi-component food-items are single food products that comprise more than one food class, brought together usually via some form of processing. Importantly, individual components of the food-item remain discernible and sensorially distinguishable from each other (e.g., chocolate chip cookies or 'choc ice'). Despite a sizable research literature on the formulation of such products, there lacks a concomitant research literature on the effect(s) of multi-component food-items (compared to single component food-items) on eating behaviour. Considerable previous research has investigated the effect of multiple separate food items on food intake, portion size selection and palatability. However, studies rarely use test foods that capture the physical or chemical interactions between components that are characteristic of multi-component foods. Nevertheless, previous research and relevant theory allow us to generate hypotheses about how multi-component foods may affect eating behaviour; consideration of food variety and perceived sensory complexity suggest that consumption of multi-component foods are likely to increase perceived palatability of such foods, self-selected portion size and food intake. Moreover, many (but not all) multi-component foods would be considered ultra-processed, which is a driver of food intake in and of itself. One possibility is that food components brought together as part of a multi-component food-item interact to strongly drive eating behaviour. To explore this idea, researchers will need to work across disciplines to address various practical and methodological barriers including the technical preparation of test foods.

Sensory and physical characteristics of foods that impact food intake without affecting acceptability: Systematic review and meta-analyses

This systematic review with meta-analyses aimed to identify the sensory and physical characteristics of foods/beverages which increase satiation and/or decrease/delay subsequent consumption without affecting acceptability. Systematic searches were first undertaken to identify review articles investigating the effects of any sensory and physical food characteristic on food intake. These articles provided some evidence that various textural parameters (aeration, hardness, homogeneity, viscosity, physical form, added water) can impact food intake. Individual studies investigating these effects while also investigating acceptability were then assessed. Thirty-seven individual studies investigated a textural manipulation and provided results on food intake and acceptability, 13 studies (27 comparisons, 898 participants) investigated effects on satiation, and 29 studies (54 comparisons, 916 participants) investigated effects on subsequent intake. Meta-analyses of within-subjects comparisons (random-effects models) demonstrated greater satiation (less weight consumed) from food products that were harder, chunkier, more viscous, voluminous, and/or solid, while demonstrating no effects on acceptability. Textural parameters had limited effects on subsequent consumption. Between-subjects studies and sensitivity analyses confirmed these results. These findings provide some evidence that textural parameters can increase satiation without affecting acceptability. The development of harder, chunkier, more viscous, voluminous, and/or solid food/beverage products may be of value in reducing overconsumption.

The social facilitation of eating: why does the mere presence of others cause an increase in energy intake?

There is strong evidence that people eat more when eating with friends and family, relative to when eating alone. This is known as the 'social facilitation of eating'. In this review, we discuss several gaps in the current scientific understanding of this phenomenon, and in doing so, highlight important areas for future research. In particular, we discuss the need for research to establish the longer-term consequences of social eating on energy balance and weight gain, and to examine whether people are aware of social facilitation effects on their own food intake. We also suggest that future research should aim to establish individual and contextual factors that moderate the social facilitation of eating (e.g. sex/gender), and it should clarify how eating socially causes people to eat more. Finally, we propose a novel evolutionary framework in which we suggest that the social facilitation of eating reflects a behavioural strategy that optimises the evolutionary fitness of individuals who share a common food resource.

Associations between number of siblings, birth order, eating rate and adiposity in children and adults

Eating quickly is associated with eating larger amounts at mealtimes and faster eaters tend to have a higher BMI. Evidence suggests that sibling structure influences the development of childhood eating behaviours. We hypothesized that number of siblings and birth order might play a role in the development of eating rate. In two UK studies, children in Bristol (n = 132; Study 1) and adults and children in London (adults n = 552, children n = 256; Study 2) reported their eating rate, number of siblings, and birth order. A BMI measurement was obtained and in Study 2 waist circumference was recorded. Ordered logistic regression was used to examine effects of sibling structure on eating rate and linear regression assessed effects of eating rate on BMI. Faster eating was associated with higher BMI and a larger waist, in children and adults (ps < .01). In Study 1, first-born children were twice as likely to eat faster compared to children who were not first-born (P < .04). In Study 2, only-child adults reported eating slower than adults who were not first-born (P < .003). Additionally, higher number of siblings was associated with faster eating rate in children from Bristol (P < .05), but not in children from London. London adults without siblings ate slower than those with two or more (P = .01), but having one sibling was associated with eating faster than having two or more (P = .01). These findings reveal how birth order and number of siblings might influence eating rate. Exploring these relationships through direct observation would be beneficial in future studies.

Recalled and momentary virtual portions created of snacks predict actual intake under laboratory stress condition

Virtual portion tasks have been used to predict food intake in healthy individuals, severity of illness in individuals with anorexia nervosa, and weight loss in bariatric surgery patients. Whether portion creation in response to a recalled interpersonal stress ("recalled stress portions") could be used as a proxy for ad lib intake, after a stressor, remains untested, and the mechanism supporting this relationship is unclear. The present study's goals were: 1) to validate virtual portion tasks as proxies for actual food intake in a stressful context and 2) to test a causal pathway in which these virtual stress portions predict ad lib intake after stress. We proposed that this relationship is mediated by virtual portions created the moment after laboratory stress or rest manipulation (momentary portions), and before the participant actually ate food. At screening, 29 healthy undergraduate white women created virtual portions of eight snacks (apples, olives, potato chips, pretzels, caramel popcorn, milk chocolate) that they typically eat and also portions they recall eating in response to a stressful interpersonal situation. In addition, after a Trier Social Stress Test, or a rest period, on separate days in counterbalanced order, participants created 'momentary' virtual portions of the same snacks presented during screening, and then were given potato chips, mini golden Oreos, and M&Ms to eat. Recalled stress (b = 0.07 ± 0.02, p = 0.003), and momentary stress (b = 0.12 ± 0.02, p = 0.00001), portions of milk chocolate accounted for 29% and 51%, respectively, of the variance in ad lib stress intake of M&Ms. Typical (b = 0.15 ± 0.07, p = 0.03), and momentary rest (b = 0.21 ± 0.06, p = 0.002), portions of chips accounted for 16% and 31%, respectively, of the variance in ad lib rest intake of chips. The causal pathway from recalled stress portion to ad lib stress snack intake was completely mediated by momentary stress portion for milk chocolate and M&Ms (β = 0.04 ± 0.02, z = 2.4, p = 0.0154). These findings illustrate the planning and recall components of eating in response to stress, but not necessarily under rest conditions. This recalled stress virtual portion paradigm has clinical and research value in that it can detect those who overconsume in response to stress.

People serve themselves larger portions before a social meal

One of the most powerful influences on food intake yet identified is the presence of familiar others at an eating occasion: people eat much more when they eat with friends/family than when they eat alone. But why this is the case is unclear. Across two studies (Study 1: N = 98; Study 2: N = 120), we found that the mere anticipation of social interaction is all that is needed to promote the selection of larger meals, and that this occurs even when a person is alone when they make their decision. Adult women served themselves larger portions when they knew they were going to eat socially versus when they knew they were going to eat alone. These data suggest that how other people influence our food intake reaches beyond the specific eating context to affect pre-meal portion size decisions, suggesting that a fundamental shift is required in our thinking about social influences on eating.

When do children learn how to select a portion size?

The reduction of portion sizes supports weight-loss. This study looks at whether children have a conceptual understanding of portion size, by studying their ability to manually serve a portion size that corresponds to what they eat. In a clinical setting, discussion around portion size is subjective thus a computerised portion size tool is also trialled, with the portion sizes chosen on the screen being compared to amounts served manually. Children (n = 76) age 5-6, 7-8 and 10-11 were asked to rate their hunger (VAS scale), liking (VAS scale) and 'ideal portion size for lunch' of eight interactive meal images using a computerised portion size tool. Children then manually self-served and consumed a portion of pasta. Plates were weighed to allow for the calculation of calories served and eaten. A positive correlation was found between manually served food portions and the amount eaten (r = 0.53, 95%CI [0.34, 0.82, P < .001), indicating that many children were able to anticipate their likely food intake prior to meal onset. A regression model demonstrates that age contributes to 9.4% of the variance in portion size accuracy (t(68) = -2.3, p = .02). There was no relationship between portion size and either hunger or liking. The portion sizes chosen on the computer at lunchtime correlated to the amount manually served overall (r = .34, 95%CI [0.07, 0.55], p < .01), but not in 5-6-year-old children. Manual portion-size selection can be observed in five-year olds and from age seven, children's 'virtual' responses correlate with their manual portion selections. The application of the computerised portion-size tool requires further development but offers considerable potential.

Reliability and responsiveness of virtual portion size creation tasks: Influences of context, foods, and a bariatric surgical procedure

Food portion size influences energy intake and sustained high-energy intake often leads to obesity. Virtual portion creation tasks (VPCTs), in which a participant creates portions of food on a computer screen, predict intake in healthy individuals. The objective of this study was to determine whether portions created in VPCTs are stable over time (test-retest reliability) and responsive to factors known to influence food intake, such as eating contexts and food types, and to determine if virtual portions can predict weight loss. Patients with obesity scheduled for bariatric surgery (n = 29), and individuals with a normal BMI (18.5-24.9 kg/m2, controls, n = 29), were instructed to create virtual portions of eight snack foods, which varied in energy density (low and high) and taste (sweet and salty). Portions were created in response to the following eating situations, or "contexts": What they would a) eat to stay healthy (healthy), b) typically eat (typical), c) eat to feel comfortably satisfied (satisfied), d) consider the most that they could tolerate eating (maximum), and e) eat if nothing was limiting them (desired). Tasks were completed before, and 3 months after, surgery in patients, and at two visits, 3 months apart, in controls. Body weight (kg) was recorded at both visits. Virtual portions differed significantly across groups, visits, eating contexts, energy densities (low vs. high), and tastes (sweet vs. salty). Portions created by controls did not change over time, while portions created by patients decreased significantly after surgery, for all contexts except healthy. For patients, desired and healthy portions predicted 3-month weight loss. VPCTs are replicable, responsive to foods and eating contexts, and predict surgical weight loss. These tasks could be useful for individual assessment of expectations of amounts that are eaten in health and disease and for prediction of weight loss.

Comparing supermarket loyalty card data with traditional diet survey data for understanding how protein is purchased and consumed in older adults for the UK, 2014-16

Background

Our ability to understand population-level dietary intake patterns is dependent on having access to high quality data. Diet surveys are common diet assessment methods, but can be limited by bias associated with under-reporting. Food purchases tracked using supermarket loyalty card records may supplement traditional surveys, however they are rarely available to academics and policy makers. The aim of our study is to explore population level patterns of protein purchasing and consumption in ageing adults (40 years onwards).

Methods

We used diet survey data from the National Diet and Nutrition Survey (2014–16) on food consumption, and loyalty card records on food purchases from a major high street supermarket retailer (2016–17) covering the UK. We computed the percentage of total energy derived from protein, protein intake per kg of body mass, and percentage of protein acquired by food type.

Results

We found that protein consumption (as the percentage of total energy purchased) increased between ages 40–65 years, and declined thereafter. In comparison, protein purchased in supermarkets was roughly 2–2.5 percentage points lower at each year of age. The proportion of adults meeting recommended levels of protein was lowest in age groups 55–69 and 70+. The time of protein consumption was skewed towards evening meals, with low intakes during breakfast or between main meals. Meat, fish and poultry dominated as sources of protein purchased and consumed, although adults also acquired a large share of their protein from dairy and bread, with little from plant protein.

Conclusions

Our study provides novel insights into how protein is purchased and consumed by ageing adults in the UK. Supermarket loyalty card data can reveal patterns of protein purchasing that when combined with traditional sources of dietary intake may enhance our understanding of dietary behaviours.

Caregiver Influences on Eating Behaviors in Young Children: A Scientific Statement From the American Heart Association

A substantial body of research suggests that efforts to prevent pediatric obesity may benefit from targeting not just what a child eats, but how they eat. Specifically, child obesity prevention should include a component that addresses reasons why children have differing abilities to start and stop eating in response to internal cues of hunger and satiety, a construct known as eating self‐regulation. This review summarizes current knowledge regarding how caregivers can be an important influence on children's eating self‐regulation during early childhood. First, we discuss the evidence supporting an association between caregiver feeding and child eating self‐regulation. Second, we discuss what implications the current evidence has for actions caregivers may be able to take to support children's eating self‐regulation. Finally, we consider the broader social, economic, and cultural context around the feeding environment relationship and how this intersects with the implementation of any actions. As far as we are aware, this is the first American Heart Association (AHA) scientific statement to focus on a psychobehavioral approach to reducing obesity risk in young children. It is anticipated that the timely information provided in this review can be used not only by caregivers within the immediate and extended family but also by a broad range of community‐based care providers.

No evidence of flavour-nutrient learning in a two-week 'home exposure' study in humans

Flavour-nutrient learning is robust in animals but remains elusive in humans. Recent evidence suggests flavour-nutrient learning may be more likely to occur with beverages that contain relatively few calories (compared to no calories), while others show that learned associations can influence satiation, without an effect on preference. The objective of this research was to determine whether acquired liking for a caloric drink could be observed in a 'home learning' context over 2 weeks, and whether it is impacted by viscosity. In combination, we also explored changes in learning relating to fullness and expected satiety. In a double-blind study, participants (N = 83; BMI = 23.3 kg/m²) were randomly allocated to one of four groups differing in either calories (0 kcal vs. 112.5 kcal) or viscosity (low vs. high) and consumed a novel-flavoured drink over 15 days. Measures of flavour (10 ml sample) and beverage liking, grip force (a measure of beverage reward value), fullness, and expected satiety were taken at the start and the end of the study. While the high-viscous beverages were less liked (M = 40.3 mm, SD = 24.7) than the low viscous beverages (M = 64.4 mm, SD = 15.3; p = .022), there was no evidence that repeated exposure to a calorie-containing beverage impacted subsequent liking for the flavour (p = .115) or for the beverage (p = .448), grip force (ps > .26), fullness, and expected satiety (ps > .12). Accordingly, we conclude that we found no evidence of flavour-nutrient learning and flavour-satiety learning. This null finding accords with previous observations indicating that humans do not acquire flavour-nutrient associations as readily as some non-human animals.

Protein Valuation in Food Choice Is Positively Associated with Lean Mass in Older Adults

BACKGROUND

Calorie for calorie, protein is more satiating than carbohydrate or fat. However, it remains unclear whether humans perceive calories derived from these macronutrients equally and whether lean mass is associated with a tendency to "value" protein when dietary decisions are made.

OBJECTIVES

This study aimed to determine the test-retest reliability of a novel method for quantifying macronutrient valuations in human volunteers and to determine whether "protein valuation" is associated with a higher fat-free mass index (FFMI) in older adults.

METHODS

A 2-alternative, forced-choice task in which 25 foods were compared in 300 trials was undertaken in 2 studies. In study 1, participants (age range 19-71 y, n = 92) attended 2 test sessions, spaced 1 wk apart. In study 2, older adults (age range 40-85 y; n = 91) completed the food-choice task and assessed the test foods for liking, expected satiety, and perceived healthiness. Body composition and habitual protein intake were assessed in both studies. Data were analyzed through the use of individual binomial logistic regressions and multilevel binomial logistic regressions.

RESULTS

In study 1, measures of macronutrient valuation showed excellent test-retest reliability; responses in the forced-choice task were highly correlated (week 1 compared with week 2; protein, r = 0.83, P < 0.001; carbohydrate, r = 0.90, P < 0.001; fat, r = 0.90, P < 0.001). Calorie for calorie, protein and carbohydrate were stronger predictors of choice than fat (P < 0.001). In study 2, protein was a stronger predictor than both carbohydrate (P = 0.039) and fat (P = 0.003), and a positive interaction was observed between protein valuation and FFMI (OR = 1.64; 95% CI: 1.38, 1.95; P < 0.001). This was the case after controlling for age, gender, liking for foods, and habitual protein consumption.

CONCLUSIONS

Together, these findings demonstrate that adult humans value calories derived from protein, carbohydrate, and fat differently, and that the tendency to value protein is associated with greater lean mass in older adults.

A systematic review and meta-analysis of the social facilitation of eating

BACKGROUND

Research suggests that people tend to eat more when eating with other people, compared with when they eat alone, and this is known as the social facilitation of eating. However, little is known about when and why this phenomenon occurs.

OBJECTIVES

This review aimed to quantify the evidence for social facilitation of eating and identify moderating factors and underlying mechanisms.

METHODS

We systematically reviewed studies that used experimental and nonexperimental approaches to examine food intake/food choice as a function of the number of co-eaters. The following databases were searched during April 2019: PsychInfo, Embase, Medline, and Social Sciences Citation Index. Studies that used naturalistic techniques were narratively synthesized, and meta-analyses were conducted to synthesize results from experimental studies.

RESULTS

We reviewed 42 studies. We found strong evidence that people select and eat more when eating with friends, compared with when they eat alone [Z = 5.32; P < 0.001; standardized mean difference (SMD) = 0.76; 95% CI: 0.48, 1.03]. The meta-analysis revealed no evidence for social facilitation across studies that had examined food intake when participants ate alone or with strangers/acquaintances (Z = 1.32; P = 0.19; SMD = 0.21, 95% CI: -0.10, 0.51). There was some evidence that the social facilitation of eating is moderated by gender, weight status, and food type. However, this evidence was limited by a lack of experimental research examining the moderating effect of these factors on the social facilitation of eating among friends. In 2 studies, there was evidence that the effect of the social context on eating may be partly mediated by longer meal durations and the perceived appropriateness of eating.

CONCLUSIONS

Findings suggest that eating with others increases food intake relative to eating alone, and this is moderated by the familiarity of co-eaters. The review identifies potential mechanisms for the social facilitation of eating and highlights the need for further research to establish mediating factors. Finally, we propose a new theoretical framework in which we suggest that the social facilitation of eating has evolved as an efficient evolutionary adaptation.

A review of evidence supporting current strategies, challenges, and opportunities to reduce portion sizes

Although there is considerable evidence for the portion-size effect and its potential impact on health, much of this has not been successfully applied to help consumers reduce portion sizes. The objective of this review is to provide an update on the strength of evidence supporting strategies with potential to reduce portion sizes across individuals and eating contexts. Three levels of action are considered: food-level strategies (targeting commercial snack and meal portion sizes, packaging, food labels, tableware, and food sensory properties), individual-level strategies (targeting eating rate and bite size, portion norms, plate-cleaning tendencies, and cognitive processes), and population approaches (targeting the physical, social, and economic environment and health policy). Food- and individual-level strategies are associated with small to moderate effects; however, in isolation, none seem to have sufficient impact on food intake to reverse the portion-size effect and its consequences. Wider changes to the portion-size environment will be necessary to support individual- and food-level strategies leading to portion control.

Portion size influences intake in Samburu Kenyan people not exposed to the Western obesogenic environment

For people in the modernized food environment, external factors like food variety, palatability, and ubiquitous learned cues for food availability can overcome internal, homeostatic signals to promote excess intake. Portion size is one such external cue; people typically consume more when served more, often without awareness. Though susceptibility to external cues may be attributed to the modernized, cue-saturated environment, there is little research on people living outside that context, or with distinctly different food norms. We studied a sample of Samburu people in rural Kenya who maintain a traditional, semi-nomadic pastoralist lifestyle, eat a very limited diet, and face chronic food insecurity. Participants (12 male, 12 female, aged 20-74, mean BMI = 18.4) attended the study on two days and were provided in counterbalanced order an individual serving bowl containing 1.4 or 2.3 kg of a familiar bean and maize stew. Amount consumed was recorded along with post-meal questions in their dialect about their awareness of intake amount. Data were omitted from two participants who consumed the entire portion in a session. Even though the 'smaller' serving was a very large meal, participants consumed 40% more when given the larger serving, despite being unable to reliably identify which day they consumed more food. This result in the Samburu demonstrates the portion size effect is not a by-product of the modern food environment and may represent a more fundamental feature of human dietary psychology.

Breaking the fast: Meal patterns and beliefs about healthy eating style are associated with adherence to intermittent fasting diets

Many believe that eating three meals each day is healthy and that skipping meals can be detrimental. What remains unclear is whether this belief undermines attempts to restrict energy intake by skipping meals. In an online survey, participants (N = 312) with experience of intermittent fasting (IF) reported their beliefs about healthy meal and snack frequency, as well as their non-fasting-dasy and fasting-day eating patterns. They also reported their level of concern with fasting-day meal patterns and their concern to generate fullness when selecting foods. Individuals currently following an IF diet (Current-IF dieters) and those who had previously attempted an IF diet but were non-adherent (Former-IF dieters) took part. Former-IF dieters were more likely to believe that it is healthy to eat three meals a day, punctuated by several snacks. On fasting-days, Former-IF dieters were also more likely to eat breakfast, a mid-morning snack, lunch, and a mid-afternoon snack whereas Current-IF dieters tended to save their eating for dinner and a late evening snack. Former-IF dieters were also more likely to be concerned about the negative consequences of missing a meal, to eat in anticipation of future hunger, and to prioritise fullness over taste when selecting foods. These findings reveal how beliefs about a healthy eating style can play an important role in shaping dietary patterns. Interventions aimed at modifying beliefs about healthy meal patterns may promote IF diet adherence.

Protein for Life: Review of Optimal Protein Intake, Sustainable Dietary Sources and the Effect on Appetite in Ageing Adults

With an ageing population, dietary approaches to promote health and independence later in life are needed. In part, this can be achieved by maintaining muscle mass and strength as people age. New evidence suggests that current dietary recommendations for protein intake may be insufficient to achieve this goal and that individuals might benefit by increasing their intake and frequency of consumption of high-quality protein. However, the environmental effects of increasing animal-protein production are a concern, and alternative, more sustainable protein sources should be considered. Protein is known to be more satiating than other macronutrients, and it is unclear whether diets high in plant proteins affect the appetite of older adults as they should be recommended for individuals at risk of malnutrition. The review considers the protein needs of an ageing population (>40 years old), sustainable protein sources, appetite-related implications of diets high in plant proteins, and related areas for future research.

Intermittent fasting, energy balance and associated health outcomes in adults: study protocol for a randomised controlled trial

Background

Prior studies have shown that intermittent fasting is capable of producing improvements in body weight and fasted health markers. However, the extent to which intermittent fasting incurs compensatory changes in the components of energy balance and its impact on postprandial metabolism are yet to be ascertained.

Methods

A total of 30–36 lean participants and 30–36 overweight/obese participants will be recruited to provide two separate study groups who will undergo the same protocol. Following an initial assessment of basic anthropometry and key health markers, measurements of habitual energy intake (weighed food and fluid intake) and physical activity energy expenditure (combined heart rate and accelerometry) will be obtained over 4 weeks under conditions of energy balance. Participants will then be randomly allocated to one of three experimental conditions for 20 days, namely (1) daily calorie restriction (reduce habitual daily energy intake by 25%), (2) intermittent fasting with calorie restriction (alternate between 24-hour periods of fasting and feeding to 150% of habitual daily energy intake), (3) intermittent fasting without calorie restriction (alternate between 24-hour periods of fasting and feeding to 200% of habitual daily energy intake). In addition to continued monitoring of energy intake and physical activity during the intervention, participants will report for laboratory-based assessments of various metabolic parameters both before and after the intervention. Specifically, fasting and postprandial measurements of resting metabolic rate, substrate oxidation, appetite, food preference, and plasma concentrations of key metabolites and hormones will be made, in addition to subcutaneous abdominal adipose tissue biopsies in the fasted state and an assessment of body composition via dual-energy x-ray absorptiometry.

Discussion

Comparing observed changes in these measures across the three intervention arms in each group will establish the impact of intermittent fasting on postprandial metabolism and the components of energy balance in both lean and overweight/obese populations. Furthermore, this will be benchmarked against current nutritional interventions for weight management and the relative contributions of negative energy balance and fasting-dependent mechanisms in inducing any observed effects will be elucidated.

Trial registration

Trial retrospectively registered at clinicaltrials.gov under reference number NCT02498002 (version: IMF-02, date: July 6, 2015).

Electronic supplementary material

The online version of this article (10.1186/s13063-018-2451-8) contains supplementary material, which is available to authorized users.

Undervalued and ignored: Are humans poorly adapted to energy-dense foods?

In many species the capacity to accurately differentiate the energy density (kcal/g) of foods is critical because it greatly improves efficiency in foraging. In modern humans this ability remains intact and is expressed in a selective preference for types of fruit and vegetables that contain more calories. However, humans evolved consuming these low energy-dense foods (typically < 1.75 kcal/g) and it remains unclear whether they can also discriminate more energy-dense foods that now feature in modern Western diets. In two experiment participants (both N = 40) completed four tasks that assessed the 'value' of different sets of 22 foods that ranged in energy density (0.1 kcal/g-5.3 kcal/g and range 0.1 kcal/g to 6.2 kcal/g in Experiment 1 and 2, respectively). In Experiment 1 three measures (expected fullness, calorie estimation, and food choice), and in foods less than approximately 1.5 kcal/g (typically fruits and vegetables), the relationship between perceived value and energy density is linear. Above this, we observed clear compressive functions, indicating relative and progressive undervaluation of higher energy-dense foods. The fourth task (rated liking) failed to provide evidence for any relationship with energy density. In Experiment 2 the same pattern was replicated in measures of expected fullness, and in two different assessments of subjective calorie content. Consistent with the concept of 'evolutionary discordance,' this work indicates that modern human physiology is poorly adapted to evaluate foods that have a historically unusual (high) energy density. This has implications both for our understanding of how 'modern' energy-dense foods affect choice and energy intake, and for strategies aimed at removing calories from highly energy-rich foods.