Integration of Sweet Taste and Metabolism Determines Carbohydrate Reward

Effect of sweet and caloric drinks on cardiac reactivity to slow-paced breathing in healthy adults

Cardiac reactivity is proposed to be a central indicator of autonomic functioning. While hyperglycemia plays a limited role in cardiac stress reactivity, it is unclear whether it may modulate cardiac reactivity in non-stressful situations. We investigated the effect of glucose on cardiac reactivity to a relaxing exercise, namely, slow-paced breathing (SPB). A total of 115 adults (age mean = 23.28 years, SD = 6.88; 76% female) either consumed a sweet & caloric, a sweet, a caloric drink, or pure water after baseline. Later, they performed a sustained attention test and SPB. Electrocardiography and impedance cardiography was obtained, and blood glucose and subjective relaxation were measured repeatedly. We analyzed changes in parasympathetic (root mean square of successive differences [RMSSD]) and sympathetic (pre-ejection period [PEP]) cardiac activity and subjective relaxation using growth curve models and performed correlational analyses. Hyperglycemia triggered cardiac PNS withdrawal and SNS activation. Despite this, SPB increased cardiac PNS activity and subjective relaxation and decreased cardiac SNS activity in all groups. Our results align with the autonomic space model and highlight the tight link between autonomic regulation and blood glucose homeostasis. Hyperglycemia might play a limited modulating role in cardiac reactivity to slow-paced breathing.

A menu for microbes: unraveling appetite regulation and weight dynamics through the microbiota-brain connection across the lifespan

Appetite, as the internal drive for food intake, is often dysregulated in a broad spectrum of conditions associated with over- and under-nutrition across the lifespan. Appetite regulation is a complex, integrative process comprising psychological and behavioral events, peripheral and metabolic inputs, and central neurotransmitter and metabolic interactions. The microbiota-gut-brain axis has emerged as a critical mediator of multiple physiological processes, including energy metabolism, brain function, and behavior. Therefore, the role of the microbiota-gut-brain axis in appetite and obesity is receiving increased attention. Omics approaches such as genomics, epigenomics, transcriptomics, proteomics, and metabolomics in appetite and weight regulation offer new opportunities for featuring obesity phenotypes. Furthermore, gut-microbiota-targeted approaches such as pre-, pro-, post-, and synbiotic, personalized nutrition, and fecal microbiota transplantation are novel avenues for precision treatments. The aim of this narrative review is 1) to provide an overview of the role of the microbiota-gut-brain axis in appetite regulation across the lifespan and 2) to discuss the potential of omics and gut microbiota-targeted approaches to deepen understanding of appetite regulation and obesity.

Neural and metabolic factors in carbohydrate reward: Rationale, design, and methods for a flavor-nutrient learning paradigm in humans

Overconsumption of ultra-processed foods (UPFs), which are linked with adverse health outcomes, is a growing public health concern. UPFs deliver highly bioavailable calories rapidly, which may contribute to their reinforcing potential and drive overconsumption. Our primary aim is to test the role of speed of nutrient availability on reward learning. We hypothesize that brain activity in reward related areas and behavioral preferences will be greater to a flavored drink predicting rapidly available calories (CS + Fast) compared with a flavored drink predicting more slowly available (CS + Slow) or no (CS-) calories. Participants (n = 64, aged 18-45 years, will consume 3 novel flavored, isosweet beverages containing 110 kcal of sucrose (CS + Fast), 110 kcal of maltodextrin (CS + Slow), or 0-kcal sucralose (CS-) 6 times in randomized, crossover order. Blood metabolites and indirect calorimetry measures, including metabolic rate and carbohydrate oxidation, will be assessed before and for 1 h after beverage consumption. Behavioral preference for beverages will be assessed in a pre- and post-test. Brain response to each flavor without calories will be assessed via functional magnetic resonance imaging in a post-test. Findings from this study will contribute to the understanding of basic mechanisms that may drive overconsumption of UPFs. Trial registration:clinicaltrials.gov registration #NCT06053294.

Postingestive reward acts through behavioral reinforcement and is conserved in obesity and after bariatric surgery

Postingestive nutrient stimulation conditions food preferences through striatal dopamine and may be associated with blunted brain responses in obesity. In a cross-sectional study, we tested flavor-nutrient conditioning (FNC) with maltodextrin-enriched yogurt, with maltodextrin previously optimized for concentration and dextrose equivalents (n = 57), and to mask texture cues (n = 102). After conditioning, healthy volunteers (n = 52) increased preference for maltodextrin-paired (+102 kcal, CS+), relative to control (+1.8 kcal, CS-) flavors, as assessed according to intake, but not pleasantness. In a clinical study (n = 61), behavioral conditioning without effects on pleasantness was confirmed across pre-bariatric candidates with obesity, weight-stable post-surgery patients, and healthy controls, without significant differences between groups. Striatal dopamine D2-like receptor (DD2lR) availability, assessed with [123I]IBZM SPECT, was reduced in the obesity group and strongly correlated with conditioning strength and a measure of restrained eating in patients with gastric bypass. These results show that postingestive nutrient stimulation influences human food choices through behavioral reinforcement, and is conserved in obesity and after bariatric surgery. Trial Registration: ISRCTN17965026: Dopaminergic neurotransmission in dietary learning and obesity.

Circular RNAs mediate the regulation of maternal placental nutrient transport and fetal development by sugar-sweetened beverages

Epidemiological and experimental studies have demonstrated a strong association between maternal diet and fetal birth weight, obesity, and metabolic syndrome. We investigated the pathways and modes of action of circular RNAs (circRNAs) that mediate the regulation of maternal reproductive performance and fetal development by sugar-sweetened beverages (20 % sucrose water, SSBs) using C57BL/6J mice as a model. Results showed that SSBs significantly increased the reproductive performance (P<0.05), body weight (P<0.01), fetal birth weight (P<0.05), placental weight (P<0.01), and the expression of nutrient transporter genes in the placenta and fetal liver (P<0.05), mainly by accelerating the maternal energy metabolism during pregnancy. However, maternal serum biochemical indices, antioxidant indices, and pathological damage to the liver and placenta predicted that the mother would be at greater health risks during this period. Moreover, transcriptomics results indicated that the differentially expressed (DE) circRNAs in the placenta regulate the maternal multiple metabolic pathways and the placental nutrient transport efficiency by sponging miRNAs and forming growth factors and proteins, ultimately improving the maternal reproductive performance. In addition, we verified the reliability of the sequencing results using reverse transcription polymerase chain reaction and identified the possibility of DE circRNAs binding to nutrient transporter genes using targeting relationship prediction. Finally, we constructed a correlation network that regulates maternal placental nutrient transport based on DE circRNAs, targeted miRNAs and nutrient transport-related genes. This study will provide scientific dietary guidance for pregnant women and new research ideas for preventing and treating pregnancy complications.

Dynamics of combatting market-driven epidemics: Insights from U.S. reduction of cigarette, sugar, and prescription opioid consumption

Misuse and overconsumption of certain consumer products have become major global risk factors for premature deaths, with their total costs in trillions of dollars. Progress in reducing such deaths has been slow and difficult. To address this challenge, this review introduces the definition of market-driven epidemics (MDEs), which arise when companies aggressively market products with proven harms, deny these harms, and resist mitigation efforts. MDEs are a specific within the broader landscape of commercial determinants of health. We selected three illustrative MDE products reflecting different consumer experiences: cigarettes (nicotine delivery product), sugar (food product), and prescription opioids (medical product). Each met the MDE case definition with proven adverse health impacts, well-documented histories, longitudinal product consumption and health impact data, and sustained reduction in product consumption. Based on these epidemics, we describe five MDE phases: market expansion, evidence of harm, corporate resistance, mitigation, and market adaptation. From the peak of consumption to the most recent data, U.S. cigarette sales fell by 82%, sugar consumption by 15%, and prescription opioid prescriptions by 62%. For each, the consumption tipping point occurred when compelling evidence of harm, professional alarm, and an authoritative public health voice and/or public mobilization overcame corporate marketing and resistance efforts. The gap between suspicion of harm and the consumption tipping point ranged from one to five decades-much of which was attributable to the time required to generate sufficient evidence of harm. Market adaptation to the reduced consumption of target products had both negative and positive impacts. To our knowledge, this is the first comparative analysis of three successful efforts to change the product consumption patterns and the associated adverse health impacts of these products. The MDE epidemiological approach of shortening the latent time to effective mitigation provides a new method to reduce the impacts of harmful products.

Investigating Taste Perception of Maltodextrins Using Lactisole and Acarbose

Previous research has demonstrated that complex carbohydrates (maltodextrins) can be perceived in the oral cavity. However, little research has been conducted to thoroughly investigate complex carbohydrate taste perception and contributing factors. This study explored the effects of the degree of polymerization and the concentration of complex carbohydrates on taste perception. Additionally, the impact of lactisole and acarbose on carbohydrate taste perception was investigated. Using a blinded, Latin Square design, participants (n = 40) received samples (control) or samples with acarbose (5 mM) or lactisole (1.4 mM). Per visit, participants received solutions: (1) short chain maltodextrin (average DP 6) (SCM), (2) long chain maltodextrin (average DP 24) (LCM), (3) maltose, and (4) glucose. Samples were evaluated in duplicate, both at low concentration and high concentration. Participants tasted the samples and rated sweetness, starchiness, and viscosity (mouthfeel) perceived on a 10 cm continuous line scale and perceived intensity on a Labelled Magnitude Scale. There was a significant effect of degree of polymerisation on sweetness (p = 0.001) and intensity (p = 0.001). For low concentration samples, no significant differences were found between LCM and acarbose LCM or SCM and acarbose SCM for sweetness, starchiness, or mouthfeel (all p > 0.05). Significant differences were observed between LCM and lactisole LCM for sweetness (1.1 ± 0.1 vs. 2.5 ± 0.3, p = 0.001), starchiness (1.4 ± 0.2 vs. 2.3 ± 0.3, p = 0.005), and mouthfeel (1.4 ± 0.2 vs. 2.3 ± 0.3, p = 0.013). In conclusion, the taste perception of maltodextrins is influenced by the degree of polymerisation. Furthermore, for this study, the sweet taste receptor was not involved in maltodextrin taste perception. While salivary α-amylase did not appear to influence taste perception with low concentration maltodextrins, further investigation is necessary.

Creation and validation of a NOVA scored picture set to evaluate ultra-processed foods

There has been a rapid shift in the modern food environment towards increased processing in foods consumed in the United States (US) and globally. The NOVA system (not an acronym) for classifying food on degree of processing currently has the most empirical support. Consumption of foods in the NOVA 4 category, ultra-processed foods (UPF), is a risk factor for a host of poor health outcomes including heart disease, stroke, and cancer. Despite these poor health outcomes, UPF make up 58% of calories consumed in the US. Methodologies for assessing the reinforcing and rewarding properties of these foods are necessary tools. The Becker-DeGroot-Marschak auction paradigm (BDM) is a well validated tool for measuring value and is amenable to neuromonitoring environments. To allow for the testing of hypotheses based on level of food processing, we present a picture set of 14 UPF and 14 minimally-processed foods (MPF) matched on visual properties, food characteristics (fat, carbohydrate, cost, etc.), and rated perceptual properties. Further, we report our scoring of these foods using the NOVA classification system and provide additional data from credentialed nutrition professionals and on inter-rater reliability using NOVA, a critique of the system. Finally, we provide all pictures, data, and code used to create this picture set as a tool for researchers.

Acute and two-week effects of neotame, stevia rebaudioside M and sucrose-sweetened biscuits on postprandial appetite and endocrine response in adults with overweight/obesity-a randomised crossover trial from the SWEET consortium

BACKGROUND

Sweeteners and sweetness enhancers (S&SE) are used to replace energy yielding sugars and maintain sweet taste in a wide range of products, but controversy exists about their effects on appetite and endocrine responses in reduced or no added sugar solid foods. The aim of the current study was to evaluate the acute (1 day) and repeated (two-week daily) ingestive effects of 2 S&SE vs. sucrose formulations of biscuit with fruit filling on appetite and endocrine responses in adults with overweight and obesity.

METHODS

In a randomised crossover trial, 53 healthy adults (33 female, 20 male) with overweight/obesity in England and France consumed biscuits with fruit filling containing 1) sucrose, or reformulated with either 2) Stevia Rebaudioside M (StRebM) or 3) Neotame daily during three, two-week intervention periods with a two-week washout. The primary outcome was composite appetite score defined as [desire to eat + hunger + (100 - fullness) + prospective consumption]/4.

FINDINGS

Each formulation elicited a similar reduction in appetite sensations (3-h postprandial net iAUC). Postprandial insulin (2-h iAUC) was lower after Neotame (95% CI (0.093, 0.166); p < 0.001; d = -0.71) and StRebM (95% CI (0.133, 0.205); p < 0.001; d = -1.01) compared to sucrose, and glucose was lower after StRebM (95% CI (0.023, 0.171); p < 0.05; d = -0.39) but not after Neotame (95% CI (-0.007, 0.145); p = 0.074; d = -0.25) compared to sucrose. There were no differences between S&SE or sucrose formulations on ghrelin, glucagon-like peptide 1 or pancreatic polypeptide iAUCs. No clinically meaningful differences between acute vs. two-weeks of daily consumption were found.

INTERPRETATION

In conclusion, biscuits reformulated to replace sugar using StRebM or Neotame showed no differences in appetite or endocrine responses, acutely or after a two-week exposure, but can reduce postprandial insulin and glucose response in adults with overweight or obesity.

FUNDING

The present study was funded by the Horizon 2020 program: Sweeteners and sweetness enhancers: Impact on health, obesity, safety and sustainability (acronym: SWEET, grant no: 774293).

Mechanisms for survival: vagal control of goal-directed behavior

Survival is a fundamental physiological drive, and neural circuits have evolved to prioritize actions that meet the energy demands of the body. This fine-tuning of goal-directed actions based on metabolic states ('allostasis') is deeply rooted in our brain, and hindbrain nuclei orchestrate the vital communication between the brain and body through the vagus nerve. Despite mounting evidence for vagal control of allostatic behavior in animals, its broader function in humans is still contested. Based on stimulation studies, we propose that the vagal afferent pathway supports transitions between survival modes by gating the integration of ascending bodily signals, thereby regulating reward-seeking. By reconceptualizing vagal signals as catalysts for goal-directed behavior, our perspective opens new avenues for theory-driven translational work in mental disorders.

Ultra-processed Food and Obesity: What Is the Evidence?

PURPOSE OF REVIEW

Obesity is a growing global healthcare concern. A proposed driver is the recent increase in ultra-processed food (UPF) intake. However, disagreement surrounds the concept of UPF, the strength of evidence, and suggested mechanisms. Therefore, this review aimed to critically appraise the evidence on UPF and obesity.

RECENT FINDINGS

Observational studies demonstrate positive associations between UPF intake, weight gain, and overweight/obesity, more clearly in adults than children/adolescents. This is supported by high-quality clinical data. Several mechanisms are proposed, but current understanding is inconclusive. Greater UPF consumption has been a key driver of obesity. There is a need to change the obesogenic environment to support individuals to reduce their UPF intake. The UPF concept is a novel approach that is not explained with existing nutrient- and food-based frameworks. Critical analysis of methodologies provides confidence, but future observational and experimental research outputs with greater methodological rigor will strengthen findings, which are outlined.

The influence of ultra-processed food consumption on reward processing and energy intake: Background, design, and methods of a controlled feeding trial in adolescents and young adults

BACKGROUND

The greatest age-related weight gain occurs in the early/mid-20s. Overall dietary quality among adolescents and emerging adults (age 18-25) is poor, with ultra-processed foods (UPF) representing more than two-thirds of adolescents' total energy intake (i.e., 68%). UPF consumption may impact cognitive and neurobiological factors that influence dietary decision-making and energy intake (EI). To date, no research has addressed this in this population.

METHODS

Participants aged 18-25 will undergo two 14-day controlled feeding periods (81% UPF, 0% UPF) using a randomly assigned crossover design, with a 4-week washout between conditions. Brain response to a UPF-rich milkshake, as well as behavioral measures of executive function, will be evaluated before and after each diet. Following each diet, measurements include ad libitum buffet meal EI, food selection, eating rate, and eating in the absence of hunger (EAH). Prior to initiating recruitment, controlled diet menus, buffet, and EAH snacks were developed and evaluated for palatability. Sensory and texture attributes of buffet and EAH snack foods were also evaluated.

RESULTS

Overall diet palatability was rated "like very much" (8)/"like moderately"(7) (UPF: 7.6 ± 1.0; Non-UPF: 6.8 ± 1.5). Subjective hardness rating (range = 1-9 [1 = soft, 9 = hard] was similar between UPF and Non-UPF buffet and snack items (UPF:4.22 ± 2.19, Non-UPF: 4.70 ± 2.03), as was the objective measure of hardness (UPF: 2874.33 ± 2497.06 g, Non-UPF: 2243.32 ± 1700.51 g).

CONCLUSIONS

Findings could contribute to an emerging neurobiological understanding of the effects of UPF consumption including energy overconsumption and weight gain among individuals at a critical developmental stage.

[Structural and functional characteristics of the brain and their role in the development of eating behaviour in obesity: A review]

Obesity is a major public health problem that requires new approaches. Despite all interventions, the behavioural and therapeutic interventions developed have demonstrated limited effectiveness in curbing the obesity epidemic. Findings from imaging studies of the brain suggest the existence of neural vulnerabilities and structural changes that are associated with the development of obesity and eating disorders. This review highlights the clinical relevance of brain neuroimaging research in obese individuals to prevent risky behaviour, early diagnosis, and the development of new safer and more effective treatments.

Effect of Non- and Low-Caloric Sweeteners on Substrate Oxidation, Energy Expenditure, and Catecholamines in Humans-A Systematic Review

The use of non- and low-caloric sweetener(s) (NCS and LCS) as a means to prevent overweight and obesity is highly debated, as both NCS and LCS have been proposed to have a negative impact on energy homeostasis. This systematic review aimed to assess the impact of NCS and LCS on fasting and postprandial substrate oxidation, energy expenditure, and catecholamines, compared to caloric sweeteners or water, across different doses and types of NCS and LCS, acutely and in the longer-term. A total of 20 studies were eligible: 16 studies for substrate oxidation and energy expenditure and four studies for catecholamines. Most studies compared the acute effects of NCS or LCS with caloric sweeteners under non-isoenergetic conditions. These studies generally found higher fat oxidation and lower carbohydrate oxidation with NCS or LCS than with caloric sweeteners. Findings for energy expenditure were inconsistent. With the limited number of studies, no convincing pattern for the remaining outcomes and comparisons could be seen. In conclusion, drinks or meals with NCS or LCS resulted in higher fat and lower carbohydrate oxidation compared to caloric sweeteners. No other conclusions could be drawn due to insufficient or inconsistent results. Further studies in this research field are warranted.

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.

Habitual daily intake of a sweet and fatty snack modulates reward processing in humans

Western diets rich in fat and sugar promote excess calorie intake and weight gain; however, the underlying mechanisms are unclear. Despite a well-documented association between obesity and altered brain dopamine function, it remains elusive whether these alterations are (1) pre-existing, increasing the individual susceptibility to weight gain, (2) secondary to obesity, or (3) directly attributable to repeated exposure to western diet. To close this gap, we performed a randomized, controlled study (NCT05574660) with normal-weight participants exposed to a high-fat/high-sugar snack or a low-fat/low-sugar snack for 8 weeks in addition to their regular diet. The high-fat/high-sugar intervention decreased the preference for low-fat food while increasing brain response to food and associative learning independent of food cues or reward. These alterations were independent of changes in body weight and metabolic parameters, indicating a direct effect of high-fat, high-sugar foods on neurobehavioral adaptations that may increase the risk for overeating and weight gain.

Evolution of beverage portion sizes consumed in Brazil between 2008 and 2018

Objective

To describe the evolution of beverage portion sizes consumed in Brazil between 2008 and 2018.

Methods

Data from the dietary surveys of 2008-2009 and 2017-2018 Brazilian Household Budget Surveys, conducted with 34,003 and 46,164 individuals, respectively, were used to analyze the portion size of beverages. Food consumption data were used to group beverages according to nutritional characteristics, type and size of portions into eight groups: high-calorie soft drinks, fruit refreshments, alcoholic beverages, coffee/tea, fruit juices, milk and milk substitutes and ultra-processed milk-based beverages. The two-day food record and recall were considered to analyze the consumed portions. Comparisons between the surveys were done using Chi-Square tests and linear regression models.

Results

Between 2008 and 2018, the average portion consumed showed a significant increase for the group of alcoholic beverages (+29%), flavored juices (+11%), caloric soft drinks (+8%), milk and milk substitutes (+6%) and fruit juices (+5%); and reduction for the coffee/tea group (-11%). Analyzes by age group showed that among individuals between 20 and 40 years of age, the soft drinks and alcoholic beverage groups showed the greatest increase in portion size, +12 and +44%, respectively.

Conclusion

The beverage portion sizes consumed in Brazil between 2008 and 2018 increased for the group of alcoholic beverages, flavored juices, caloric soft drinks, milk and milk substitutes, and fruit juices.

Enhanced sweet taste perception in obesity: Joint analysis of gustatory data from multiple studies

Introduction

While sweet taste perception is a potential determinant of feeding behavior in obesity, the supporting evidence is inconsistent and is typically associated with methodological limitations. Notably, possible associations between sweet taste perception and measures of food reward remain undetermined.

Materials and methods

We conducted a cross-sectional analysis comparing 246 individuals with severe obesity and 174 healthy volunteers using a validated method for taste perception assessment. We included gustatory variables, namely intensity and pleasantness ratings of sour, salt, sweet, and bitter tastants, and taste thresholds assessed by electrogustometry. Reward-related feeding behavior, including hedonic hunger, food addiction, feeding behavior traits, and acceptance of foods and alcohol, was evaluated using self-rated scales for comparison with gustatory measures.

Result

In logistic regressions adjusted for age, gender, educational level, and research center, we found that a greater likelihood of belonging to the obesity group was associated with higher sweet intensity ratings (OR = 1.4, P = 0.01), hedonic hunger, food addiction symptoms, restrained and emotional eating (1.7 < OR ≤ 4.6, all P ≤ 0.001), and lower alcohol acceptance (OR = 0.6, P = 0.0002). Using principal component analysis, we found that while hedonic hunger, food addiction, and emotional eating were strongly interrelated, they were not associated with sweet intensity perception that, in turn, had a closer relationship with alcohol acceptance and restrained eating.

Conclusion

We found that individuals with obesity report higher sweet taste intensity ratings than healthy controls. Furthermore, while psychological measures of reward-related feeding behavior assess a common construct, sweet intensity perception may represent a different obesity-related dimension.

"Liking" as an early and editable draft of long-run affective value

Psychological and neural distinctions between the technical concepts of "liking" and "wanting" pose important problems for motivated choice for goods. Why could we "want" something that we do not "like," or "like" something but be unwilling to exert effort to acquire it? Here, we suggest a framework for answering these questions through the medium of reinforcement learning. We consider "liking" to provide immediate, but preliminary and ultimately cancellable, information about the true, long-run worth of a good. Such initial estimates, viewed through the lens of what is known as potential-based shaping, help solve the temporally complex learning problems faced by animals.

How we decide what to eat: Toward an interdisciplinary model of gut-brain interactions

Everyday dietary decisions have important short-term and long-term consequences for health and well-being. How do we decide what to eat, and what physiological and neurobiological systems are involved in those decisions? Here, we integrate findings from thus-far separate literatures: (a) the cognitive neuroscience of dietary decision-making, and (b) growing evidence of gut-brain interactions and especially influences of the gut microbiome on diet and health outcomes. We review findings that suggest that dietary decisions and food consumption influence nutrient sensing, homeostatic signaling in the gut, and the composition of the gut microbiome. In turn, the microbiome can influence host health and behavior. Through reward signaling pathways, the microbiome could potentially affect food and drink decisions. Such bidirectional links between gut microbiome and the brain systems underlying dietary decision-making may lead to self-reinforcing feedback loops that determine long-term dietary patterns, body mass, and health outcomes. This article is categorized under: Economics > Individual Decision-Making Psychology > Brain Function and Dysfunction Psychology > Reasoning and Decision Making.

Visual cues associated with sweet taste increase short-term eating and grab attention in healthy volunteers

Most studies that examine responses to food cues use images of actual foods as stimuli. Since foods are rewarding in multiple ways, it then becomes difficult to try and partial out the role of the importance of different aspects of food reward. Here we aimed to evaluate the impact of novel visual cues specifically associated with the immediate sensory reward from a liked sweet taste. In the training phase, one visual cue (CSsweet) was associated with the experience of sweet taste (10%sucrose) and a second, control cue (CSneutral) with a neutral taste (artificial saliva) using a disguised training procedure. In Experiment 1, participants (n = 45) were given an ad libitum snack intake test 30 min post-training, either labelled with CSsweet or CSneutral. Total caloric consumption was significantly higher in the CSsweet (650 ± 47 kcal) than CSneutral (477 ± 45 kcal) condition, but ratings of liking for the snacks did not differ significantly between conditions. In Experiment 2, participants (n = 80) exhibited an overall attentional bias (22.1 ± 9.9 ms) for the CSsweet relative to CSneutral cue (assessed using a dot-probe task), however rated liking for the CSsweet did not change significantly after cue-sweet training. Likewise, measures of expected satiety for drinks labelled with CSsweet did not differ significantly from CSneutral. Overall these two experiments provide evidence that associations between neutral visual cues and the experience of a liked sweet taste leads to cue-potentiated eating in the presence of the CSsweet cue. With no evidence that cue-sweet training altered rated liking for the visual cues, and in keeping with extant literature on the dissociation of hedonic and rewarding properties of food rewards, we propose this potentiation effect to reflect increased incentive salience.

Effects of psychological, sensory, and metabolic energy prime manipulation on the acute endocrine stress response in fasted women

The stress response supports survival through energy mobilization. Paradoxically, a low blood glucose level dampens the endocrine stress response, and sugar consumption prior to stress restores it. Thus, energy availability may play a causal role in the endocrine stress response. Yet, it has never been tested whether sweet taste or expectations towards a drink content modulate the stress response. We investigated the potential role of sweetness, energy load and expectations towards energy load of a drink consumed prior to stress in restoring stress reactivity after fasting. N = 152 women (meanage=21.53, sdage=2.61) participated in the Trier Social Stress Test for groups in the morning after an overnight fast. Prior to stress induction, participants consumed a drink containing saccharose (sugar, n = 51), an equally sweet drink containing non-caloric sweetener (sweetener, n = 46), or water (n = 56). Additionally, participants in the sugar and sweetener group (n = 97) were informed whether or not their drink contained any calories (energy prime), which was deceptive in 50% of the cases. Eight salivary cortisol (-30, -20, -10, 0, +12, +25, +35, +45 min) and three blood glucose samples (-30, 0, +25 min) were assessed throughout the experiment. The effects of the experimental manipulations on cortisol trajectories were tested using multilevel mixed models. We found that compared with water, sugar and sweetener both significantly increased cortisol stress reactivity and with comparable intensity. However, our sensitivity analysis revealed a significant effect of sugar on cortisol trajectories compared to water and to sweetener. Drink-induced changes in blood glucose concentration were not associated with increases in cortisol. The energy prime did not affect the stress response. Overall, we could replicate the boosting effect of sugar consumption in a female sample after 8 h of fasting. The specific contribution of sweet taste and metabolic hormones to this boosting effect should be tested more rigorously in sex-balanced designs in the future.

Reconsolidation of a post-ingestive nutrient memory requires mTOR in the central amygdala

The central control of feeding behavior and metabolic homeostasis has been proposed to involve a form of post-ingestive nutrient learning independent of the gustatory value of food. However, after such learning, it is unknown which brain regions or circuits are activated to retrieve the stored memory and whether this memory undergoes reconsolidation that depends on protein synthesis after its reactivation through retrieval. In the present study, using a conditioned-flavor-preference paradigm by associating flavors with intra-gastric infusion of glucose to minimize the evaluation of the taste of food, we show that retrieval of the post-ingestive nutrient-conditioned flavor memory stimulates multiple brain regions in mice, including the central nucleus of the amygdala (CeA). Moreover, memory retrieval activated the mammalian target of rapamycin complex 1 (mTORC1) in the CeA, while site-specific or systemic inhibition of mTORC1 immediately after retrieval prevented the subsequent expression of the post-ingestive nutrient-associated flavor memory, leading to a long-lasting suppression of reinstatement. Taken together, our findings suggest that the reconsolidation process of a post-ingestive nutrient memory modulates food preferences.

Monitoring In Vivo Neural Activity to Understand Gut-Brain Signaling

Appropriate food intake requires exquisite coordination between the gut and the brain. Indeed, it has long been known that gastrointestinal signals communicate with the brain to promote or inhibit feeding behavior. Recent advances in the ability to monitor and manipulate neural activity in awake, behaving rodents has facilitated important discoveries about how gut signaling influences neural activity and feeding behavior. This review emphasizes recent studies that have advanced our knowledge of gut-brain signaling and food intake control, with a focus on how gut signaling influences in vivo neural activity in animal models. Moving forward, dissecting the complex pathways and circuits that transmit nutritive signals from the gut to the brain will reveal fundamental principles of energy balance, ultimately enabling new treatment strategies for diseases rooted in body weight control.

Understanding sweet-liking phenotypes and their implications for obesity: Narrative review and future directions

Building on a series of recent studies that challenge the universality of sweet liking, here we review the evidence for multiple sweet-liking phenotypes which strongly suggest, humans fall into three hedonic response patterns: extreme sweet likers (ESL), where liking increases with sweetness, moderate sweet likers (MSL), who like moderate but not intense sweetness, and sweet dislikers (SD), who show increasing aversion as sweetness increases. This review contrasts how these phenotypes differ in body size and composition, dietary intake and behavioural measures to test the widely held view that sweet liking may be a key driver of obesity. Apart from increased consumption of sugar-sweetened beverages in ESL, we found no clear evidence that sweet liking was associated with obesity and actually found some evidence that SD, rather than ESL, may have slightly higher body fat. We conclude that ESL may have heightened awareness of internal appetite cues that could protect against overconsumption and increased sensitivity to wider reward. We note many gaps in knowledge and the need for future studies to contrast these phenotypes in terms of genetics, neural processing of reward and broader measures of behaviour. There is also the need for more extensive longitudinal studies to determine the extent to which these phenotypes are modified by exposure to sweet stimuli in the context of the obesogenic environment.

Confection Confusion: Interplay Between Diet, Taste, and Nutrition

Although genetics shapes our sense of taste to prefer some foods over others, taste sensation is plastic and changes with age, disease state, and nutrition. We have known for decades that diet composition can influence the way we perceive foods, but many questions remain unanswered, particularly regarding the effects of chemosensory plasticity on feeding behavior. Here, we review recent evidence on the effects of high-nutrient diets, especially high dietary sugar, on sweet taste in vinegar flies, rodents, and humans, and discuss open questions about molecular and neural mechanisms and research priorities. We also consider ways in which diet-dependent chemosensory plasticity may influence food intake and play a role in the etiology of obesity and metabolic disease. Understanding the interplay between nutrition, taste sensation, and feeding will help us define the role of the food environment in mediating chronic disease and design better public health strategies to combat it.

Glucose and fat sensing in the human hypothalamus

Energy balance is centrally regulated by the brain through several interacting neuronal systems involving external, peripheral, and central factors within the brain. The hypothalamus integrates these factors and is the key brain area in the regulation of energy balance. In this review, we will explain the structure of the hypothalamus and its role in the regulation of energy balance. An important part of energy balance regulation is the sensing of nutrient status and availability. This review will focus on the sensing of the two main sources of energy by the hypothalamus: glucose and fat. As many common health problems and chronic diseases can be traced back to a disrupted hypothalamic function, we will also discuss hypothalamic sensing of glucose and fats in these pathologies. Finally, we will summarize the current knowledge and discuss how this may be applied clinically and for future research perspectives.

Perspective: Measuring Sweetness in Foods, Beverages, and Diets: Toward Understanding the Role of Sweetness in Health

Various global public health agencies recommend minimizing exposure to sweet-tasting foods or beverages. The underlying rationale is that reducing exposure to the perception of sweet tastes, without regard to the source of sweetness, may reduce preferences for sweetness, added sugar intake, caloric intake, and body weight. However, the veracity of this sequence of outcomes has yet to be documented, as revealed by findings from recent systematic reviews on the topic. Efforts to examine and document the effects of sweetness exposure are needed to support evidence-based recommendations. They require a generally agreed-upon methodology for measuring sweetness in foods, beverages, and the overall diet. Although well-established sensory evaluation techniques exist for individual foods in laboratory settings, they are expensive and time-consuming, and agreement on the optimal approach for measuring the sweetness of the total diet is lacking. If such a measure could be developed, it would permit researchers to combine data from different studies and populations and facilitate the design and conduct of new studies to address unresolved research questions about dietary sweetness. This narrative review includes an overview of available sensory techniques, their strengths and limitations, recent efforts to measure the sweetness of foods and diets across countries and cultures, and a proposed future direction for improving methods for measuring sweetness toward developing the data required to support evidence-based recommendations around dietary sweetness.

Chemospecific deficits in taste sensitivity following bilateral or right hemispheric gustatory cortex lesions in rats

Our prior studies showed bilateral gustatory cortex (GC) lesions significantly impair taste sensitivity to salts (NaCl and KCl) and quinine ("bitter") but not to sucrose ("sweet"). The range of qualitative tastants tested here has been extended in a theoretically relevant way to include the maltodextrin, Maltrin, a preferred stimulus by rats thought to represent a unique taste quality, and the "sour" stimulus citric acid; NaCl was also included as a positive control. Male rats (Sprague-Dawley) with histologically confirmed neurotoxin-induced bilateral (BGCX, n = 13), or right (RGCX, n = 13) or left (LGCX, n = 9) unilateral GC lesions and sham-operated controls (SHAM, n = 16) were trained to discriminate a tastant from water in an operant two-response detection task. A mapping system was used to determine placement, size, and symmetry (when bilateral) of the lesion. BGCX significantly impaired taste sensitivity to NaCl, as expected, but not to Maltrin or citric acid, emulating our prior results with sucrose. However, in the case of citric acid, there was some disruption in performance at higher concentrations. Interestingly, RGCX, but not LGCX, also significantly impaired taste sensitivity, but only to NaCl, suggesting some degree of lateralized function. Taken together with our prior findings, extensive bilateral lesions in GC do not disrupt basic taste signal detection to all taste stimuli uniformly. Moreover, GC lesions do not preclude the ability of rats to learn and perform the task, clearly demonstrating that, in its absence, other brain regions are able to maintain sensory-discriminative taste processing, albeit with attenuated sensitivity for select stimuli.

Satiety, Taste and the Cephalic Phase: A Crossover Designed Pilot Study into Taste and Glucose Response

The glycemic response produced by a food depends on both the glycemic index of the food itself, and on how the body reacts to the food as it is consumed and digested, in turn dependent on sensory cues. Research suggests that taste stimulation can induce the cephalic phase insulin response before food has reached the digestion, priming the body for an incoming glucose load. This glycemic response can consequently affect the amount of food consumed in a subsequent meal. The aim of this study was to investigate the effects on satiety of four preloads that differed in caloric content and sensory properties, in a small group of female and male participants (n = 10). Water, sucrose, sucralose, and maltodextrin were used to represent 4 different conditions of the preload, with or without energy, and with or without sweet taste. Individual plasma glucose concentrations were sampled at baseline, 45 min after consuming the preload, and after consuming an ad-libitum test meal. Hunger, fullness, desire to eat, and thoughts of food feeling were assessed every 15 min using visual analog scales. Results in male participants when comparing two solutions of equal caloric content, maltodextrin and sucrose, showed that plasma glucose concentration spiked in the absence of taste input (p = 0.011). Maltodextrin, while providing calories does not have the sweet taste that can serve to trigger cephalic phase insulin release to attenuate an incoming glucose load, and was accompanied by significantly greater change in feelings of satiety than with the other preloads. Despite the difference in postprandial blood glucose, the energy consumed in the test meal across the treatments was not significantly different in either males or females. Results highlight the importance of taste in stimulating the body for the efficient and effective glucose homeostasis.

Deep Representational Similarity Learning for Analyzing Neural Signatures in Task-based fMRI Dataset

Similarity analysis is one of the crucial steps in most fMRI studies. Representational Similarity Analysis (RSA) can measure similarities of neural signatures generated by different cognitive states. This paper develops Deep Representational Similarity Learning (DRSL), a deep extension of RSA that is appropriate for analyzing similarities between various cognitive tasks in fMRI datasets with a large number of subjects, and high-dimensionality - such as whole-brain images. Unlike the previous methods, DRSL is not limited by a linear transformation or a restricted fixed nonlinear kernel function - such as Gaussian kernel. DRSL utilizes a multi-layer neural network for mapping neural responses to linear space, where this network can implement a customized nonlinear transformation for each subject separately. Furthermore, utilizing a gradient-based optimization in DRSL can significantly reduce runtime of analysis on large datasets because it uses a batch of samples in each iteration rather than all neural responses to find an optimal solution. Empirical studies on multi-subject fMRI datasets with various tasks - including visual stimuli, decision making, flavor, and working memory - confirm that the proposed method achieves superior performance to other state-of-the-art RSA algorithms.

A Gut Feeling about Dopamine

In this issue of Neuron, Fernandes et al. (2020) compare intra-gastric sugar and non-caloric sweetener to investigate how post-ingestive effects can be reinforcing, revealing a role for the hepatic vagus nerve in transforming sugar sensing by the gut into behavioral reinforcement via midbrain dopamine neuron responses.

FGF21 Signals to Glutamatergic Neurons in the Ventromedial Hypothalamus to Suppress Carbohydrate Intake

Fibroblast growth factor 21 (FGF21) is an endocrine hormone produced by the liver that regulates nutrient and metabolic homeostasis. FGF21 production is increased in response to macronutrient imbalance and signals to the brain to suppress sugar intake and sweet-taste preference. However, the central targets mediating these effects have been unclear. Here, we identify FGF21 target cells in the hypothalamus and reveal that FGF21 signaling to glutamatergic neurons is both necessary and sufficient to mediate FGF21-induced sugar suppression and sweet-taste preference. Moreover, we show that FGF21 acts directly in the ventromedial hypothalamus (VMH) to specifically regulate sucrose intake, but not non-nutritive sweet-taste preference, body weight, or energy expenditure. Finally, our data demonstrate that FGF21 affects neuronal activity by increasing activation and excitability of neurons in the VMH. Thus, FGF21 signaling to glutamatergic neurons in the VMH is an important component of the neurocircuitry that functions to regulate sucrose intake.

Vagus nerve stimulation boosts the drive to work for rewards

Interoceptive feedback transmitted via the vagus nerve plays a vital role in motivation by tuning actions according to physiological needs. Whereas vagus nerve stimulation (VNS) reinforces actions in animals, motivational effects elicited by VNS in humans are still largely elusive. Here, we applied non-invasive transcutaneous auricular VNS (taVNS) on the left or right ear while participants exerted effort to earn rewards using a randomized cross-over design (vs. sham). In line with preclinical studies, acute taVNS enhances invigoration of effort, and stimulation on the left side primarily facilitates invigoration for food rewards. In contrast, we do not find conclusive evidence that acute taVNS affects effort maintenance or wanting ratings. Collectively, our results suggest that taVNS enhances reward-seeking by boosting invigoration, not effort maintenance and that the stimulation side affects generalization beyond food reward. Thus, taVNS may enhance the pursuit of prospective rewards which may pave avenues to treat motivational deficiencies.

The vagus nerve transmits signals between the gut and the brain thereby tuning motivated behavior to physiological needs. Here, the authors show that acute non-invasive stimulation of the vagus nerve via the ear enhances the invigoration of effort for rewards.

Effects of Non-nutritive Sweeteners on Sweet Taste Processing and Neuroendocrine Regulation of Eating Behavior

PURPOSE OF REVIEW

Non-nutritive sweeteners (NNS) are increasingly used as a replacement for nutritive sugars as means to quench the desire for "sweets" while contributing few or no dietary calories. However, there is concern that NNS may uncouple the evolved relationship between sweet taste and post-ingestive neuroendocrine signaling. In this review, we examine the effects of NNS exposure on neural and peripheral systems in humans.

RECENT FINDINGS

NNS exposure during early development may influence sweet taste preferences, and NNS consumption might increase motivation for sweet foods. Neuroimaging studies provide evidence that NNS elicit differential neuronal responsivity in areas related to reward and satiation, compared with caloric sweeteners. Findings are heterogenous regarding whether NNS affect physiological responses. Additional studies are warranted regarding the consequences of NNS on metabolic outcomes and neuroendocrine pathways. Given the widespread popularity of NNS, future studies are essential to establish their role in long-term health.

Fructose vs glucose decreased liking/wanting and subsequent intake of high-energy foods in young women

Recent research on the health impacts of added sugar has prompted the comparison of the effects of its 2 major components: glucose and fructose. Fructose was identified as a risk factor for obesity and metabolic syndrome. However, because of the differences in metabolic responses and responsivity of reward circuitry to palatable food, it is unknown if glucose and fructose induce similar appetite-related responses in humans with varying weights. This study compared the behavioral responses to food in young women of a healthy weight (n = 31) and with excess weight (n = 28). We hypothesized that (1) the inhibitory effect of glucose (vs fructose) on food-related responses would be greater in subjects of a healthy weight than in those with overweight/obesity and (2) subjects with overweight/obesity would exhibit a stronger preference for food than subjects with a healthy weight. After an overnight fast, the subjects ingested a glucose or equienergetic fructose beverage on 2 separate days, respectively. Then, they completed liking and wanting ratings and 2 decision-making tasks followed by ad libitum food intake. The results revealed that fructose reduced both liking and wanting for food in subjects with overweight/obesity and also decreased energy intake in all subjects. Relative to the healthy-weight group, subjects with overweight/obesity preferred the immediate reward. Moreover, only in the healthy-weight group were liking and wanting scores for food positively associated with actual food consumption. Overall, fructose (vs glucose) showed an acute inhibitory effect on appetite-related responses in subjects with excess weight.

Studies of human twins reveal genetic variation that affects dietary fat perception

To learn more about the mechanisms of human dietary fat perception, 398 human twins rated fattiness and liking for six types of potato chips that differed in triglyceride content (2.5, 5, 10, and 15% corn oil); reliability estimates were obtained from a subset (n = 50) who did the task twice. Some chips also had a saturated long-chain fatty acid (hexadecanoic acid, 16:0) added (0.2%) to evaluate its effect on fattiness and liking. We computed the heritability of these measures and conducted a genome-wide association study (GWAS) to identify regions of the genome that co-segregate with fattiness and liking. Perceived fattiness and liking for the potato chips were reliable (r = 0.31-0.62, p < 0.05) and heritable (up to h2 = 0.29, p < 0.001, for liking). Adding hexadecanoic acid to the potato chips significantly increased ratings of fattiness but decreased liking. Twins with the G allele of rs263429 near GATA3-AS1 or the G allele of rs8103990 within ZNF729 reported more liking for potato chips than did twins with the other allele (multivariate GWAS, p < 1×10-5), with results reaching genome-wide suggestive but not significance criteria. Person-to-person variation in the perception and liking of dietary fat was (a) negatively affected by the addition of a saturated fatty acid and (b) related to inborn genetic variants. These data suggest liking for dietary fat is not due solely to fatty acid content and highlight new candidate genes and proteins within this sensory pathway.

Stimulation of the vagus nerve reduces learning in a go/no-go reinforcement learning task

When facing decisions to approach rewards or to avoid punishments, we often figuratively go with our gut, and the impact of metabolic states such as hunger on motivation are well documented. However, whether and how vagal feedback signals from the gut influence instrumental actions is unknown. Here, we investigated the effect of non-invasive transcutaneous auricular vagus nerve stimulation (taVNS) vs. sham (randomized cross-over design) on approach and avoidance behavior using an established go/no-go reinforcement learning paradigm in 39 healthy human participants (23 female) after an overnight fast. First, mixed-effects logistic regression analysis of choice accuracy showed that taVNS acutely impaired decision-making, p = .041. Computational reinforcement learning models identified the cause of this as a reduction in the learning rate through taVNS (∆α = -0.092, p_boot = .002), particularly after punishment (∆α_Pun = -0.081, p_boot = .012 vs. ∆α_Rew =-0.031, p_boot = .22). However, taVNS had no effect on go biases, Pavlovian response biases or response time. Hence, taVNS appeared to influence learning rather than action execution. These results highlight a novel role of vagal afferent input in modulating reinforcement learning by tuning the learning rate according to homeostatic needs.

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.

Short-Term Consumption of Sucralose with, but Not without, Carbohydrate Impairs Neural and Metabolic Sensitivity to Sugar in Humans

There is a general consensus that overconsumption of sugar-sweetened beverages contributes to the prevalence of obesity and related comorbidities such as type 2 diabetes (T2D). Whether a similar relationship exists for no- or low-calorie "diet" drinks is a subject of intensive debate and controversy. Here, we demonstrate that consuming seven sucralose-sweetened beverages with, but not without, a carbohydrate over 10 days decreases insulin sensitivity in healthy human participants, an effect that correlates with reductions in midbrain, insular, and cingulate responses to sweet, but not sour, salty, or savory, taste as assessed with fMRI. Taste perception was unaltered and consuming the carbohydrate alone had no effect. These findings indicate that consumption of sucralose in the presence of a carbohydrate rapidly impairs glucose metabolism and results in longer-term decreases in brain, but not perceptual sensitivity to sweet taste, suggesting dysregulation of gut-brain control of glucose metabolism.

Food reward and gut-brain signalling

The increasing availability of ultra-processed, energy dense food is contributing to the spread of the obesity pandemic, which is a serious health threat in today’s world. One possible cause for this association arises from the fact that the brain is wired to derive pleasure from eating. Specifically, food intake activates reward pathways involving dopamine receptor signalling. The reinforcing value of specific food items results from the interplay between taste and nutritional properties. Increasing evidence suggests that nutritional value is sensed in the gut by chemoreceptors in the intestinal tract and the hepatic portal vein, and conveyed to the brain through neuronal and endocrine pathways to guide food selection behaviour. Ultra-processed food is designed to potentiate the reward response through a combination of high fat and high sugar, therebye seeming highly appetizing. There is increasing evidence that overconsumption of processed food distorts normal reward signalling, leading to compulsive eating behaviour and obesity. Hence, it is essential to understand food reward and gut-brain signalling to find an effective strategy to combat the obesity pandemic.

Effects of Sucralose Ingestion versus Sucralose Taste on Metabolic Responses to an Oral Glucose Tolerance Test in Participants with Normal Weight and Obesity: A Randomized Crossover Trial

Here, we tested the hypothesis that sucralose differentially affects metabolic responses to labeled oral glucose tolerance tests (OGTTs) in participants with normal weight and obesity. Participants (10 with normal weight and 11 with obesity) without diabetes underwent three dual-tracer OGTTs preceded, in a randomized order, by consuming sucralose or water, or by tasting and expectorating sucralose (e.g., sham-fed; sweetness control). Indices of β-cell function and insulin sensitivity (S_I) were estimated using oral minimal models of glucose, insulin, and C-peptide kinetics. Compared with water, sucralose ingested (but not sham-fed) resulted in a 30 ± 10% increased glucose area under the curve in both weight groups. In contrast, the insulin response to sucralose ingestion differed depending on the presence of obesity: decreased within 20–40 min of the OGTT in normal-weight participants but increased within 90–120 min in participants with obesity. Sham-fed sucralose similarly decreased insulin concentrations within 60 min of the OGTT in both weight groups. Sucralose ingested (but not sham-fed) increased S_I in normal-weight participants by 52 ± 20% but did not affect S_I in participants with obesity. Sucralose did not affect glucose rates of appearance or β-cell function in either weight group. Our data underscore a physiological role for taste perception in postprandial glucose responses, suggesting sweeteners should be consumed in moderation.

Chronic exposure to liquid sucrose and dry sucrose diet have differential effects on peripheral taste responses in female rats

Sugar-sweetened beverages are the major source of added calories in the Western diet and their prevalence is associated with obesity and metabolic disruption. Despite the critical role of the taste system in determining food selection and consumption, the effects of chronic sucrose consumption on the peripheral taste system in mammals have received limited attention. We offered female Sprague Dawley rats free access to water and one of three diets for up to 40 days: (1) sucrose-free chow or "NS" diet; (2) a high-sucrose dry diet or "HS"; or (3) 30% sucrose solution and the NS diet, designated "LiqS" diet. Sucrose consumption by LiqS rats gradually increased and by day 14 was equal to that of HS rats. Food intake decreased in LiqS rats, but their energy intake remained higher than for NS or HS rats. There was no significant difference in weight gain of the groups during the study. Recordings from the chorda tympani nerve (CT), which innervates taste buds on the anterior tongue, revealed decreased responses to 1 M sucrose in both LiqS and HS rats and to acesulfame K and salt tastants in LiqS rats after 40 days on diet. Umami, bitter, and acid response magnitudes were unchanged in both groups. These results demonstrate that chronic sucrose exposure inhibits taste responses to higher concentrations of sweet stimuli. More surprisingly, CT responses to NaCl and 0.5M NaAc were significantly reduced in rats on the LiqS diet. Thus, the physical form of the diet influences taste responsiveness to salt and sweet taste function. These data suggest that taste buds are previously unappreciated targets of chronic sucrose consumption.

Revisited: Assessing the in vivo data on low/no-calorie sweeteners and the gut microbiota

Over the last two decades, safety concerns about low/no-calorie sweeteners (LNCS) have been described in the archival scientific literature including elevated risk of metabolic syndrome, type 2 diabetes, excessive weight gain, cardiovascular disease, safety, and disruption of the gut microbiome. A recent review by Lobach, Roberts, and Roland in Food and Chemical Toxicology examined 17 research articles on modulation of gut bacteria by LNCS along with other selected publications. In the conclusions of their paper, they claim that LNCS 1) do not affect gut microbiota at use levels and 2) are safe at levels approved by regulatory agencies. Both of these claims are incorrect. The scientific literature on LNCS clearly indicates that it is inappropriate to draw generalized conclusions regarding effects on gut microbiota and safety issues for compounds that vary widely chemical structure and pharmacokinetics. Scientific studies on the sweetener sucralose, used here as a representative LNCS, indicate that this organochlorine compound unequivocally and irrefutably disrupts the gut microbiome at doses relevant to human use. Results of dozens of additional research publications added and reviewed here also raise significant and extensive concerns about the safety of sucralose for the human food supply.