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.

A social norm intervention increases liking and intake of whole crickets, and what this tells us about food disgust.

Edible insects are healthy and sustainable but are rejected as food in Western populations due to disgust. We tested the effectiveness of written interventions to reduce disgust and increase intake of whole crickets. Cricket acceptance after reading a descriptive social norm or food preparation intervention passage was compared with a control passage, and an unfamiliar but non-disgusting food ('leblebi' - roasted chickpeas). Participants (N = 120) were randomised to one of four conditions (control + crickets, food preparation + crickets, social norm + crickets and control + leblebi). Outcome measures included taste pleasantness, desire to eat, food intake and, to measure disgust, self-report disgust, tactile sensitivity and latency to eat. In the control condition, crickets were rejected due to disgust and low desire to eat. In comparison, in the social norm condition, crickets were rated as tasting more pleasant, more desirable, and less disgusting, and intake was greater. The food preparation passage had a small but positive effect on cricket intake. For the first time, this study shows that a descriptive social norm can affect eating behaviour even when a food is disgusting; however, a food preparation intervention cannot overcome high disgust. The pattern of results suggested that expected and perceived taste pleasantness affects disgust. Therefore, taste quality and normalising consumption are targets for promoting acceptance of insects, and probably other novel, sustainable foods.

It tastes OK, but I don't want to eat it: New insights into food disgust.

To better understand food-disgust, we investigated the long-standing theory that disgust towards a food causes it to taste 'bad'. To induce disgust, participants were served cookies labelled as containing crickets (Study 1); or served whole crickets versus novel (leblebi) and familiar (peanuts) control foods (Study 2). Participants (Study 1: N = 80; Study 2: N = 90) tasted the foods and rated taste pleasantness, desire to eat, disgust and, in Study 1, 16 taste attributes (e.g., nuttiness). Latency to eat and food intake were included as behavioural indicators of disgust. In both studies disgusting foods were presumed to taste bad, but this was disconfirmed after tasting - disgust did not cause the food to taste bad. Nonetheless, the taste attribute results suggested increased attention towards cricket flavours/textures. Furthermore, desire to eat and intake results suggested that disgust, but not novelty, was associated with reduced food wanting. Even if a disgust-inducing food tastes OK, people do not 'want' to consume it. By offering novel insights into our understanding of disgust, these results may stimulate progress in new avenues of emotion research, as well as informing the development of methods to reduce disgust and increase the acceptance of novel, sustainable, foods. For example, interventions should encourage tasting to overcome negative expectations of taste pleasantness and should tackle low levels of wanting, e.g., by normalising consumption of the target food.

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.

Consumers' attitudes towards alternatives to conventional meat products: Expectations about taste and satisfaction, and the role of disgust.

The livestock sector has environmental, health, and animal welfare impacts. This UK-based, quantitative study aimed to elucidate consumers' valuation of alternatives to conventional meat products. In an online study, 151 meat eaters and 44 non-meat eaters were shown pictures of meat, dairy, and bakery products, including beef burger, cheese sandwich and blueberry muffin. Each product was evaluated with three different labels (e.g., 'conventional', 'plant-based' and 'cultured' for beef burger). Participants rated expected taste pleasantness, fullness, satisfaction, healthiness, disgust and willingness-to-pay for each product/label combination. The results obtained demonstrate that alternatives to conventional meat products overall are acceptable to both meat and non-meat eaters. Although meat eaters' expected plant-based meat alternatives to be less satisfying, due to lower expected taste pleasantness and fillingness (Cohen's d = 0.14 to 0.63), they perceived the plant-based alternatives to be more healthy (d ≥ 1.18). Cultured meat products were perceived by meat eaters to be equally or more healthy, but more disgusting (d ≥ 0.41), than conventional meat products. These results suggest there is an opportunity to promote (motivate) acceptance of alternatives to conventional meat products based on their perceived healthiness, to at least partly balance reduced expected taste pleasantness and other negative attributes (i.e., barriers).

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.

Restricting sugar or carbohydrate intake does not impact physical activity level or energy intake over 24 h despite changes in substrate use: a randomised crossover study in healthy men and women.

PURPOSE: To determine the effects of dietary sugar or carbohydrate restriction on physical activity energy expenditure, energy intake, and physiological outcomes across 24 h. METHODS: In a randomized, open-label crossover design, twenty-five healthy men (n = 10) and women (n = 15) consumed three diets over a 24-h period: moderate carbohydrate and sugar content (MODSUG = 50% carbohydrate [20% sugars], 15% protein, 35% fat); low sugar content (LOWSUG = 50% carbohydrate [< 5% sugars], 15% protein, 35% fat); and low carbohydrate content (LOWCHO = 8% carbohydrate [< 5% sugars], 15% protein, 77% fat). Postprandial metabolic responses to a prescribed breakfast (20% EI) were monitored under laboratory conditions before an ad libitum test lunch, with subsequent diet and physical activity monitoring under free-living conditions until blood sample collection the following morning. RESULTS: The MODSUG, LOWSUG and LOWCHO diets resulted in similar mean [95%CI] rates of both physical activity energy expenditure (771 [624, 919] vs. 677 [565, 789] vs. 802 [614, 991] kcal·d-1; p = 0.29] and energy intake (2071 [1794, 2347] vs. 2195 [1918, 2473] vs. 2194 [1890, 2498] kcal·d-1; P = 0.34), respectively. The LOWCHO condition elicited the lowest glycaemic and insulinaemic responses to breakfast (P < 0.01) but the highest 24-h increase in LDL-cholesterol concentrations (P < 0.001), with no differences between the MODSUG and LOWSUG treatments. Leptin concentrations decreased over 24-h of consuming LOWCHO relative to LOWSUG (p < 0.01). CONCLUSION: When energy density is controlled for, restricting either sugar or total dietary carbohydrate does not modulate physical activity level or energy intake over a 24-h period (~ 19-h free-living) despite substantial metabolic changes. CLINICAL TRIALS REGISTRATION ID: NCT03509610, https://clinicaltrials.gov/show/NCT03509610.

Preference for high-carbohydrate foods does not change for children and adolescents in insulin-induced hypoglycemia.

INTRODUCTION: Hypoglycemia elicits coordinated counter-regulatory neuroendocrine responses. The extent to which this process involves an increased drive to eat, together with greater preference for foods high in carbohydrate content, is unclear. Our objective was to examine this effect in children and adolescents (age 5-19 years) without diabetes and no prior known experience of hypoglycemic episodes. RESEARCH DESIGN AND METHODS: We administered a computerised task designed to examine preference for high-carbohydrate foods (sweet and savory) to pediatric patients (n=26) undergoing an insulin tolerance test as part of the routine clinical assessment of pituitary hormone secretory capacity. The task was completed at baseline and three time points after intravenous infusion of insulin (approximately 7, 20 and 90 min). RESULTS: Although all patients reached insulin-induced hypoglycemia (mean venous glucose at nadir=1.9 mmol/L), there was moderate evidence of no effect on preference for high-carbohydrate foods (moderate evidence for the null hypothesis) compared with euglycemia. Patients also did not display an increase in selection of foods of high compared with low energy density. Sensitivity of the task was demonstrated by decreased preference for sweet, high-carbohydrate foods after consumption of sweet food and drink. CONCLUSIONS: Results support the view that acute hypoglycemia does not automatically prompt the choice of high-carbohydrate foods for rapid glucose restoration, and further stresses the importance that people and families with children vulnerable to hypoglycemic episodes ensure that 'rapidly absorbed glucose rescue therapy' is always available.

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.

Consumption of low-calorie sweetened drinks is associated with 'sweet satiation', but not with 'sweet-taste confusion': A virtual study.

Originating from studies on rats, the 'taste confusion' hypothesis predicts that exposure to low-calorie sweeteners (LCS) will impair compensatory responses to sugar intake, resulting in increased overall calorie intake. We conducted a virtual study in which young adult human participants (n = 332), who differed in their history of exposure to sweet drinks (e.g., drank 'diet' (LCS) soft drinks or 'regular' (sugar-sweetened) soft drinks), imagined consuming a cheese sandwich and two-thirds of a 500 ml drink (still water, sparkling water, diet Coca Cola, regular Coca Cola, or semi-skimmed milk), or no drink, as a hypothetical lunch-time meal. They then used a screen-based tool to select the amount of a sweet snack (chocolate M&M's) or savoury snack (salted peanuts) that they would eat immediately with the remaining third of their drink (i.e., a total of 12 drink and snack combinations per participant). The results were inconsistent with the predictions of the taste confusion hypothesis; specifically, the extent to which consumption of sugar cola compared with water (still or sparkling) reduced snack intake did not differ between habitual diet (LCS) and habitual sugar soft-drink consumers. Other results showed a 'sweet satiation' effect (i.e., lower sweet versus savoury snack intake when the drink accompanying the meal was sweet compared with when it was water), and negligible compensation in snack food intake for the difference in the energy content of diet versus sugar cola.

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.

Varied Effects of COVID-19 Chemosensory Loss and Distortion on Appetite: Implications for Understanding Motives for Eating and Drinking.

A common symptom of COVID-19 is altered smell and taste. This qualitative study sought to further characterise this altered chemosensory perception and its effects on appetite for food and drink. Eighteen women and two men who had experienced chemosensory loss associated with COVID-19 participated in semi-structured interviews. Thematic analysis of the interview transcripts revealed five major themes. These confirmed that all participants had experienced an altered sense of smell (anosmia, and less frequently parosmia and phantosmia) of variable duration. Loss of taste (ability to detect sweetness, saltiness, etc.) was less common. Participants experienced decreased, no change or increased appetite, with six participants reporting weight loss. Consistent with evidence linking diminished appetite with inflammation, for two participants, decreased appetite preceded anosmia onset. Anosmia reduced enjoyment of food and drink. Compensatory strategies included choosing salty, sweet and 'spicy' foods, and increased attention to food texture, and there was evidence that the postingestive rewarding effects of food intake were also important for maintaining appetite. Some participants mentioned increased alcohol intake, in part facilitated by reduced intensity of disliked flavours of alcoholic drinks. The narratives also underlined the value placed on the sociability and structuring of time that daily meals provide. This research adds to the record and analysis of lived experiences of altered chemosensory perception resulting from SARS-CoV-2 infection, and it contributes insights concerning the role of smell and flavour in motivating and rewarding food ingestion.

Stress, caffeine and psychosis-like experiences-A double-blind, placebo-controlled experiment.

OBJECTIVE: Psychosis-like perceptual distortions can occur in the general population, and both stress and caffeine can enhance the proneness to psychosis-like experiences, such as hallucinations. The current study aims to explore the effects of acute caffeine intake and acute stress on perceptual distortions in a double-blind, placebo-controlled experiment. METHODS: Regular caffeine consumers (n = 92) and non/low consumers (n = 89) were assigned to 100 mg caffeine/placebo and stress/no stress conditions. The White Christmas Paradigm (WCP) was used to measure hallucination-like symptoms, and bias towards threat-related words was used as an indicator of persecutory ideation. Participants reported their daily caffeine intake, and completed the State-Trait Anxiety Inventory, the Launay-Slade Hallucination Scale, the Persecutory Ideation Questionnaire and the Marlow-Crowne Social Desirability Scale. RESULTS: Acute stress slightly increased hallucination-like experiences, but not recall bias, while the small amount of caffeine had a time-dependent effect on recall bias. Proneness to persecutory ideation was positively and social desirability was negatively correlated with recall bias towards threat-related words, while proneness to hallucinations positively correlated with hallucination-like experiences. CONCLUSIONS: Our results indicate that psychosocial stress-in line with the diathesis-stress model-can lead to the enhancement of hallucination-like experiences.

Associations between plasma fatty acid concentrations and schizophrenia: a two-sample Mendelian randomisation study.

BACKGROUND: Although studies suggest that concentrations of omega-3 and omega-6 fatty acids are lower in individuals with schizophrenia, evidence for beneficial effects of fatty acid supplementation is scarce. Therefore, in this study, we aimed to determine whether omega-3 and omega-6 fatty acid concentrations are causally related to schizophrenia. METHODS: We did a two-sample Mendelian randomisation study, using deidentified summary-level data that were publicly available. Exposure-outcome relationships were evaluated using the inverse variance weighted two-sample Mendelian randomisation method using results from genome-wide association studies (GWASs) of fatty acid concentrations and schizophrenia. GWAS results were available for European (fatty acids) and European and Asian (schizophrenia) ancestry samples. Overall age and gender information were not calculable from the summary-level GWAS results. Weighted median, weighted mode, and Mendelian randomisation Egger regression methods were used as sensitivity analyses. To address underlying mechanisms, further analyses were done using single instruments within the FADS gene cluster and ELOVL2 gene locus. FADS gene cluster and ELOVL2 gene causal effects on schizophrenia were calculated by dividing the single nucleotide polymorphism (SNP)-schizophrenia effect estimate by the SNP-fatty acid effect estimate with standard errors derived using the first term from a delta method expansion for the ratio estimate. Multivariable Mendelian randomisation was used to estimate direct effects of omega-3 fatty acids on schizophrenia, independent of omega-6 fatty acids, lipoproteins (ie, HDL and LDL), and triglycerides. FINDINGS: Mendelian randomisation analyses indicated that long-chain omega-3 and long-chain omega-6 fatty acid concentrations were associated with a lower risk of schizophrenia (eg, inverse variance weighted odds ratio [OR] 0·83 [95% CI 0·75-0·92] for docosahexaenoic acid). By contrast, there was weak evidence that short-chain omega-3 and short-chain omega-6 fatty acids were associated with an increased risk of schizophrenia (eg, inverse variance weighted OR 1·07 [95% CI 0·98-1·18] for α-linolenic acid). Effects were consistent across the sensitivity analyses and the FADS single-SNP analyses, suggesting that long-chain omega-3 and long-chain omega-6 fatty acid concentrations were associated with lower risk of schizophrenia (eg, OR 0·74 [95% CI 0·58-0·96] for docosahexaenoic acid) whereas short-chain omega-3 and short-chain omega-6 fatty acid concentrations were associated with an increased risk of schizophrenia (eg, OR 1·08 [95% CI 1·02-1·15] for α-linolenic acid). By contrast, estimates from the ELOVL2 single-SNP analyses were more imprecise and compatible with both risk-increasing and protective effects for each of the fatty acid measures. Multivariable Mendelian randomisation indicated that the protective effect of docosahexaenoic acid on schizophrenia persisted after conditioning on other lipids, although evidence was slightly weaker (multivariable inverse variance weighted OR 0·84 [95% CI 0·71-1·01]). INTERPRETATION: Our results are compatible with the protective effects of long-chain omega-3 and long-chain omega-6 fatty acids on schizophrenia, suggesting that people with schizophrenia might have difficulty converting short-chain polyunsaturated fatty acids to long-chain polyunsaturated fatty acids. Further studies are required to determine whether long-chain polyunsaturated fatty acid supplementation or diet enrichment might help prevent onset of schizophrenia. FUNDING: National Institute for Health Research Biomedical Research Centre at University Hospitals Bristol and Weston NHS Foundation Trust and the University of Bristol.

No effects of sweet taste exposure at breakfast for 3 weeks on pleasantness, desire for, sweetness or intake of other sweet foods: a randomised controlled trial.

This work investigated the effects of repeated sweet taste exposure at breakfast on perceptions and intakes of other sweet foods, while also examining the effects due to duration of exposure (1/3 weeks), test context (breakfast/lunch) and associations between taste perceptions and intakes. Using a randomised controlled parallel-group design, participants (n 54, 18 male, mean age: 23·9 (sd 5·8) years, mean BMI: 23·6 (sd 3·5) kg/m2) were randomised to consume either a sweet breakfast (cereal with sucralose) (n 27) or an equienergetic non-sweet breakfast (plain cereal) (n 27) for 3 weeks. On days 0 (baseline), 7 and 21, pleasantness, desire to eat and sweetness were rated for other sweet and non-sweet foods and sweet food consumption was assessed in an ad libitum meal at breakfast and lunch. Using intention-to-treat analyses, no statistically significant effects of exposure were found at breakfast (largest F2,104 = 1·84, P = 0·17, ηp2 = 0·03) or lunch (largest F1,52 = 1·22, P = 0·27, ηp2 = 0·02), and using Bayesian analyses, the evidence for an absence of effect in all rating measures was strong to very strong (smallest BF01 = 297·97 (BF01error = 2·68 %)). Associations between ratings of pleasantness, desire to eat and intake were found (smallest r = 0·137, P < 0·01). Effects over time regardless of exposure were also found: sugars and percentage energy consumed from sweet foods increased throughout the study (smallest (F2,104 = 4·54, P = 0·01, ηp2 = 0·08). These findings demonstrate no effects of sweet taste exposure at breakfast for 1 or 3 weeks on pleasantness, desire for, sweetness or intakes of other sweet foods in either the same (breakfast) or in a different (lunch) meal context.