Connecting biology with psychology to make sense of appetite control

An all 2D bio-inspired gustatory circuit for mimicking physiology and psychology of feeding behavior

Animal behavior involves complex interactions between physiology and psychology. However, most AI systems neglect psychological factors in decision-making due to a limited understanding of the physiological-psychological connection at the neuronal level. Recent advancements in brain imaging and genetics have uncovered specific neural circuits that regulate behaviors like feeding. By developing neuro-mimetic circuits that incorporate both physiology and psychology, a new emotional-AI paradigm can be established that bridges the gap between humans and machines. This study presents a bio-inspired gustatory circuit that mimics adaptive feeding behavior in humans, considering both physiological states (hunger) and psychological states (appetite). Graphene-based chemitransistors serve as artificial gustatory taste receptors, forming an electronic tongue, while 1L-MoS2 memtransistors construct an electronic-gustatory-cortex comprising a hunger neuron, appetite neuron, and feeding circuit. This work proposes a novel paradigm for emotional neuromorphic systems with broad implications for human health. The concept of gustatory emotional intelligence can extend to other sensory systems, benefiting future humanoid AI.

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.

Apple versus chocolate: Evidence for discrimination of distension-related and calorie-related satiety signals in post-prandial fullness and hunger, and in the quality and location of other body sensations

Gastric distension and detection of macronutrients (calories) in the gut are determinants of satiation and satiety. We tested effects of these variables on body sensations after eating, and their connection with visual-analogue scale (VAS) hunger and fullness ratings. Participants completed VAS ratings and quality and location of body sensations tasks after consumption of milk chocolate (38 g, 200 kcal) versus fresh apple fruit matched for weight (38 g, 20 kcal) and matched for calories (380 g, 200 kcal). Effects of food weight (380 vs 38 g) were large and located predominantly in the abdominal region. They also occupied a greater body area and occurred sooner after eating than effects related to calories (200 vs 20 kcal). The same pattern was apparent in the results from the quality of sensations task. VAS ratings indicated that hunger was affected by food volume and calories, whereas fullness was affected primarily by food volume. Together, these results provide evidence of dissociation of the perceived after-effects of food ingestion related to food volume and food calorie content in humans. Additionally, the studies demonstrate the utility of two rarely used, semi-quantitative tasks, which generate information on the identity, intensity, valence, and location of eating-related sensations.

Attitudes to Three Weight Maintenance Strategies: A Qualitative Study

Weight loss maintenance can be difficult and ultimately unsuccessful, due to psychological, behavioural, social, and physiological influences. The present study investigated three strategies with the potential to improve weight maintenance success: daily weighing, missing an occasional meal, habitually changing high energy foods. The principal aim was to gain an understanding of attitudes to these strategies in participants who had recent experience of weight loss attempts, with or without maintenance. This was a qualitative study involving semi-structured interviews, with 20 participants aged 18–67 (twelve females), analysed using thematic analysis. Most participants disliked daily weighing and missing an occasional meal for long-term maintenance and were concerned about potential negative effects on mental health. All participants had experience of habitual changes to high energy foods and regarded this strategy as obvious and straightforward. Replacement of high energy foods was favoured over elimination. Participants preferred strategies that felt flexible, “normal” and intuitive and disliked those that were thought to have a negative impact on mental health. Further investigation is needed on whether concerns regarding mental health are well founded and, if not, how the strategies can be made more acceptable and useful.

"This snack is too small - I'll take a different one": Quantifying 'norm' and 'choice' boundaries to inform effective portion-reduction strategies

Previous research suggests that portion sizes can be categorised as 'normal' or 'abnormal' and that reduced portions which are still categorised as normal do not promote compensatory responses in intake. However, a critical question remains - will consumers choose a reduced portion product from among standard portion competitors? For the first time, we explore the effects of portion reduction on food choice. Participants (N = 45) categorised 20 different portions (range 40-420 kcal) of five snacks as normal or abnormal (to quantify individual 'norm boundaries' for each food) and rated their desire to eat each snack. Using a 2-alternative forced choice hypothetical task, we then calculated a 'choice boundary' by offering smaller portions of their most-desired snack (range 40-240 kcal) alongside standardised portions (240 kcal) of the less-desired foods. Boundaries were derived using probit analysis (choice boundary mean = 185.8 kcal, SD = 54, norm boundary mean = 127.3 kcal, SD = 49.5) and these deviated significantly (p < .01, d = 0.98, mean difference = 58.0 kcal, SD = 59.1). Critically, this shows that only a small reduction - where the product is still considered normal - can nudge a consumer to select an alternative. Choice boundaries were also affected by differences in desire to eat; when two foods were desired to a similar degree, only minor reductions in the size of the favourite food elicited a switch in choice. Together, these findings indicate that portion reduction can also influence food choice, highlighting the importance of measuring choice boundaries before reformulating commercial products.

A two-component pictured-based appetite assessment tool is capable of detecting appetite sensations in younger children: A pilot study

Visual analogue scales (VAS) have commonly been used to assess appetite in children 8 years and older; however, these tools have been considered unreliable for children 7 years old and under. The objective of this pilot study was to develop a picture-based appetite assessment (PBAA) tool for children aged 4-10 years and pilot test it compared to a VAS-based appetite assessment. The study hypothesis was that the PBAA scores would decrease following the consumption of an ad libitum snack compared to the scores in the fasted state in children 4 to 10 years old; furthermore, there would be a good level of agreement (intraclass correlation coefficients >0.75) between the appetite scores by the PBAA and VAS tools in children aged 8 years or older. At Visit 1, in a fasted state, all children (n = 15) completed the PBAA. Children who were 8-10 years old (n = 8) also completed the VAS-based appetite assessment. Then, an ad libitum snack was provided, and appetite assessments were repeated at 5-, 30- and 60-minutes post-snack. The same assessments were completed at visit 2 pre (fasting)- and post-consumption of a snack containing 25% of the amount consumed at visit 1 (limited snack). PBAA scores were different across time (P < .001) and between types of meal (ad libitum vs limited snack) (P = .015) in all children. A good agreement between the PBAA and VAS scores at 30 and 60 minutes after both types of meal was found (intraclass correlation coefficients >0.75). The PBAA tool was able to detect expected changes in appetite sensations and was in good agreement with the VAS instrument.

Identifying Barriers to Reducing Portion Size: A Qualitative Focus Group Study of British Men and Women

Reducing portion size might reduce meal satisfaction, which could minimize adherence to portion size interventions. The present study sought to identify the perceived barriers for consumers to eat smaller portions. A secondary aim explored the relative contribution of enjoyment of taste and post-meal fullness as determinants of meal satisfaction. Focus groups (N = 42) evaluated consumers' feelings toward a small reduction in portion size. Thematic analysis of written free association tasks and open-ended group discussions revealed that most participants expected to feel hungry and unsatisfied, which motivated them to consume something else. However, others expected to feel comfortable, healthy, and virtuous. The acceptability of the reduced portion was also determined by meal characteristics (e.g., time and setting) and individual characteristics (e.g., predicted energy requirements). Compared to post-meal fullness, enjoyment of taste was perceived to be the more important determinant of meal satisfaction. In conclusion, interventions should present portion reduction as a marginal modification with little physiological consequence to energy reserves, while emphasizing the positive feelings (e.g., comfort, satisfaction, and self-worth) experienced after consuming a smaller portion. Additionally, focusing on taste enjoyment (rather than fullness) might be a useful strategy to maintain meal satisfaction despite a reduction in meal size.

Food portion size influences accompanying beverage selection in adults

When trying to reduce food portion size, it is important that meal satisfaction is, as far as possible, preserved. Otherwise, individuals may select accompaniments to the meal (e.g., snacks, beverages) to achieve satisfaction and, in doing so, negate any benefit of the original portion size reduction. This study investigated whether varying portion sizes of food would influence choice of accompanying beverages. That is, when presented with a food portion size that is smaller or larger than their ideal, an individual may compensate by choosing a beverage based on its satiating and/or orosensory properties to balance the expected satiation and satisfaction of a meal. Data from an online interactive study (n = 93) was analysed using multilevel ordinal logistic regression models. Food portion size (100, 300, 500, 700, or 900 kcal) predicted beverage choice (water, low-energy sweetened beverage, high-energy sweetened beverage). For example, the sweetened beverages were more likely to be selected with small food portion sizes (p < .001). Participant ideal food portion size did not interact with this relationship. Participants appear to have recognised that sweetened beverages provide flavour and/or energy, and used them to compensate for a smaller meal. While switching to a low-energy beverage with an increased food portion size is advantageous for energy balance, choosing a high-energy beverage with a decreased food portion size is likely to be detrimental for those attempting to reduce energy intake and body weight.

Slow Down: Behavioural and Physiological Effects of Reducing Eating Rate

Slowing eating rate appears to be an effective strategy for reducing food intake. This feasibility study investigated the effect of eating rate on post-meal responses using functional magnetic resonance imaging (fMRI), plasma gastrointestinal hormone concentrations, appetite ratings, memory for recent eating, and snack consumption. Twenty-one participants (mean age 23 years with healthy body mass index) were randomly assigned to consume a 600 kcal meal at either a “normal” or “slow” rate (6 vs. 24 min). Immediately afterwards, participants rated meal enjoyment and satisfaction. FMRI was performed 2-h post-meal during a memory task about the meal. Appetite, peptide YY, and ghrelin were measured at baseline and every 30 min for 3 h. Participants were given an ad-libitum snack three hours post-meal. Results were reported as effect sizes (Cohen’s d) due to the feasibility sample size. The normal rate group found the meal more enjoyable (effect size = 0.5) and satisfying (effect size = 0.6). Two hours post-meal, the slow rate group reported greater fullness (effect size = 0.7) and more accurate portion size memory (effect sizes = 0.4), with a linear relationship between time taken to make portion size decisions and the BOLD response in satiety and reward brain regions. Ghrelin suppression post-meal was greater in the slow rate group (effect size = 0.8). Three hours post-meal, the slow rate group consumed on average 25% less energy from snacks (effect size = 0.5). These data offer novel insights about mechanisms underlying how eating rate affects food intake and have implications for the design of effective weight-management interventions.

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.

Combating Excessive Eating: A Role for Four Evidence-Based Remedies

OBJECTIVE

The aim of this study is to review the control of energy balance and outline some causes of and remedies for excessive energy intake.

METHODS

A narrative review was conducted.

RESULTS

There is negative feedback control of energy intake and body weight, but, nonetheless, energy intake is only loosely coupled with energy expenditure. Consequently, we are vulnerable to eating in excess of energy requirements. In this context, energy density, portion size, and habitual meal patterns have strong influences on energy intake and, accordingly, can be targeted to reduce energy intake. For example, energy density can be reduced without much affecting food reward (approximately the pleasure gained from eating) because their relationship is such that reward value is affected relatively little by increments in energy density above 1.5 kcal/g. This and other strategies that increase reward per calorie eaten may be superior to increasing the satiety effect of products because fullness is not inherently rewarding. Low-calorie sweeteners provide a means to reduce energy density while largely preserving food or beverage reward value. Consistent with this, consumption of low-calorie sweeteners compared with consumption of sugars has been found to reduce energy intake and body weight.

CONCLUSIONS

Understanding what causes excessive eating also provides insights into how to combat this problem.

A Comparison of the Satiety Effects of a Fruit Smoothie, Its Fresh Fruit Equivalent and Other Drinks

Energy-containing liquids are claimed to have relatively low satiating power, although energy in liquids is not without effect on appetite. Using the preload test-meal method, effects on fullness and energy intake compensation were compared across four drinks (water, blackcurrant squash, milk and fruit smoothie) and the fresh fruit equivalent of the smoothie. Preload volumes were similar, and the energy value of each preload was 569 kJ, except for water (0 kJ). Healthy, adult participants rated the preloads for liking, enjoyment, satisfaction, familiarity and how ‘food-like’ they seemed. The preload to test-meal interval was 2 min (n = 23) or 2 h (n = 24). The effects of the preloads on fullness varied with food-likeness and the rate at which they were consumed. In contrast, energy intake compensation versus water did not differ between the energy-containing preloads, although it decreased over time (from 82% at 2 min to 12% at 2 h). In conclusion, although fullness increased with food-likeness, subsequent energy intake compensation did not differ for energy/nutrients consumed in drinks compared with a food. The results also support the proposal that food intake is influenced predominantly by the immediate, but rapidly waning, post-ingestive effects of the previous ‘meal’ (rather than by changes in energy balance).

The role of low-calorie sweeteners in the prevention and management of overweight and obesity: evidence v. conjecture

By virtue of reducing dietary energy density, low-calorie sweeteners (LCS) can be expected to decrease overall energy intake and thereby decrease body weight. Such effects will be limited by the amount of sugar replaced by LCS, and the dynamics of appetite and weight control (e.g., acute compensatory eating, and an increase in appetite and decrease in energy expenditure accompanying weight loss). Consistent with these predictions, short-term intervention studies show incomplete compensation for the consumption of LCS v. sugar, and longer-term intervention studies (from 4 weeks to 40 months duration) show small decreases in energy intake and body weight with LCS v. sugar. Despite this evidence, there are claims that LCS undermine weight management. Three claims are that: (1) LCS disrupt the learned control of energy intake (sweet taste confusion hypothesis); (2) exposure to sweetness increases desire for sweetness (sweet tooth hypothesis); (3) consumers might consciously overcompensate for 'calories saved' when they know they are consuming LCS (conscious overcompensation hypothesis). None of these claims stands up to close examination. In any case, the results of the intervention studies comparing LCS v. sugar indicate that the effect of energy dilution outweighs any tendency LCS might conceivably have to increase energy intake.

What can the food and drink industry do to help achieve the 5% free sugars goal?

AIMS

To contribute evidence and make recommendations to assist in achieving free sugars reduction, with due consideration to the broader picture of weight management and dietary quality.

METHODS

An expert workshop in July 2016 addressed options outlined in the Public Health England report 'Sugar reduction: The evidence for action' that related directly to the food industry. Panel members contributed expertise in food technology, public heath nutrition, marketing, communications, psychology and behaviour. Recommendations were directed towards reformulation, reduced portion sizes, labelling and consumer education. These were evaluated based on their feasibility, likely consumer acceptability, efficacy and cost.

RESULTS

The panel agreed that the 5% target for energy from free sugars is unlikely to be achievable by the UK population in the near future, but a gradual reduction from average current level of intake is feasible. Progress requires collaborations between government, food industry, non-government organisations, health professionals, educators and consumers. Reformulation should start with the main contributors of free sugars in the diet, prioritising those products high in free sugars and relatively low in micronutrients. There is most potential for replacing free sugars in beverages using high-potency sweeteners and possibly via gradual reduction in sweetness levels. However, reformulation alone, with its inherent practical difficulties, will not achieve the desired reduction in free sugars. Food manufacturers and the out-of-home sector can help consumers by providing smaller portions. Labelling of free sugars would extend choice and encourage reformulation; however, government needs to assist industry by addressing current analytical and regulatory problems. There are also opportunities for multi-agency collaboration to develop tools/communications based on the Eatwell Guide, to help consumers understand the principles of a varied, healthy, balanced diet.

CONCLUSION

Multiple strategies will be required to achieve a reduction in free sugars intake to attain the 5% energy target. The panel produced consensus statements with recommendations as to how this might be achieved.