Lipids and obesity: Also a matter of taste?

A new perspective on obesity: perception of fat taste and its relationship with obesity

Background: Obesity, which results from a long-term positive energy balance, is affected by many factors, especially nutrition. The sensory properties of foods are associated with increased food intake through hedonic appetite. Taste perception, a component of flavor, is also responsible for increased consumption, through reward and hedonic mechanisms. Foods with high fat and energy content are among the foods that create the reward perception. The perception of fat taste, the primary taste that has recently entered the literature, may also be associated with increased food consumption and body weight. Therefore, in this review, the relationship between fat taste and obesity is examined, using the latest literature.

RESULTS

Different hypotheses have been proposed regarding the mechanism of the relationship between fat-taste perception and obesity, such as hedonic appetite, microbiota, decreased taste perception, and increased taste threshold level. In addition, some studies examining this relationship reported significant associations between the level of fat-taste perception and obesity, whereas others did not find a significant difference.

CONCLUSION

Considering the prevalence and contribution to obesity of Western-style nutrition, characterized by high amounts of fat and sugar consumption, elucidating this relationship may be an essential solution for preventing and treating obesity.

Prolonged latency of the gustatory evoked potentials for sucrose solution in subjects living with obesity compared with normal-weight subjects

OBJECTIVES

A difference in cortical treatment of taste information could alter food intake promoting the development of obesity. The main purpose was to compare, in subjects living with obesity (OB) and normal-weight subjects (NW), the characteristics of gustatory evoked potentials (GEP) for sucrose solution (10 g.100 mL-1) before and after a standard lunch. The secondary objective was to evaluate the correlations between GEP and the plasmatic levels of acylated ghrelin, leptin, insulin and serotonin.

METHODS

Each subject had 2 randomized sessions spaced by an interval of 2 days. During one session, subjects were fasting and during the other, subjects took a lunch low in sugar. In each session, subjects had a blood test before a first GEP recording followed by a second GEP recording either after a lunch (feeding session) or no lunch (fasting session).

RESULTS

Twenty-eight OB (BMI: 38.6 ± 9.0 kg.m-2) were matched to 22 NW (BMI: 22.3 ± 2.2 kg.m-2). GEP latencies were prolonged in OB regardless the sessions and the time before and after lunch, compared with NW (in Cz at the morning: 170 ± 33 ms vs 138 ± 25 ms respectively; p < 0.001). The increase in latency observed in NW after lunch was not observed in OB. Negative or positive correlations were noted in all participants between GEP latencies and ghrelin, leptin, insulin plasmatic levels (P1Cz, r = -0.38, r = 0.33, r = 0.37 respectively, p < 0.0001).

CONCLUSIONS

This study highlights a slower activation in the taste cortex in OB compared with NW.

A specific tongue microbiota signature is found in patients displaying an improvement of orosensory lipid perception after a sleeve gastrectomy

Introduction

A preferential consumption of low-fat foods is reported by most of the patients after a vertical sleeve gastrectomy (VSG). The fact that a recent study shed light on a relationship between oral microbiota and fat taste sensitivity in obese patients prompted us to explore whether such a connection also exists in the context of a VSG.

Methods

Thirty-two adult female patients with a severe obesity (BMI = 43.1 ± 0.7 kg/m²) and candidates for a VSG were selected. Oral microbiota composition surrounding the gustatory circumvallate papillae (CVP) and the lipid perception thresholds were explored before and 6 months after surgery.

Results

VSG was found to be associated both with a qualitative (compositional changes) and quantitative (lower gene richness) remodeling of the peri-CVP microbiota. Analysis of the lipid perception allowed us to distinguish two subgroups: patients with a post-operative improvement of the fat taste sensitivity (i.e., with a lower threshold, n = 14) and unimproved patients (n = 18). Specific peri-CVP microbiota signatures also discriminated these two subgroups, unimproved patient being characterized by higher levels of Porphyromonas, Fusobacterium, and Haemophilus genera associated with lower levels of Atopobium and Prevotella genera as compared to the lipid-improved patients.

Conclusion

Collectively, these data raise the possibility that the microbial environment surrounding gustatory papillae might play a role in the positive changes of fat taste sensitivity observed in some patients after VSG.

Taste of Fat and Obesity: Different Hypotheses and Our Point of View

Obesity results from a temporary or prolonged positive energy balance due to an alteration in the homeostatic feedback of energy balance. Food, with its discriminative and hedonic qualities, is a key element of reward-based energy intake. An alteration in the brain reward system for highly palatable energy-rich foods, comprised of fat and carbohydrates, could be one of the main factors involved in the development of obesity by increasing the attractiveness and consumption of fat-rich foods. This would induce, in turn, a decrease in the taste of fat. A better understanding of the altered reward system in obesity may open the door to a new era for the diagnosis, management and treatment of this disease.

CD36 maintains the gastric mucosa and associates with gastric disease

The gastric epithelium is often exposed to injurious elements and failure of appropriate healing predisposes to ulcers, hemorrhage, and ultimately cancer. We examined the gastric function of CD36, a protein linked to disease and homeostasis. We used the tamoxifen model of gastric injury in mice null for Cd36 (Cd36-/-), with Cd36 deletion in parietal cells (PC-Cd36-/-) or in endothelial cells (EC-Cd36-/-). CD36 expresses on corpus ECs, on PC basolateral membranes, and in gastrin and ghrelin cells. Stomachs of Cd36-/- mice have altered gland organization and secretion, more fibronectin, and inflammation. Tissue respiration and mitochondrial efficiency are reduced. Phospholipids increased and triglycerides decreased. Mucosal repair after injury is impaired in Cd36-/- and EC-Cd36-/-, not in PC-Cd36-/- mice, and is due to defect of progenitor differentiation to PCs, not of progenitor proliferation or mature PC dysfunction. Relevance to humans is explored in the Vanderbilt BioVu using PrediXcan that links genetically-determined gene expression to clinical phenotypes, which associates low CD36 mRNA with gastritis, gastric ulcer, and gastro-intestinal hemorrhage. A CD36 variant predicted to disrupt an enhancer site associates (p < 10-17) to death from gastro-intestinal hemorrhage in the UK Biobank. The findings support role of CD36 in gastric tissue repair, and its deletion associated with chronic diseases that can predispose to malignancy.

Do Gut Microbes Taste?

Gut microbiota has emerged as a major metabolically active organ with critical functions in both health and disease. The trillions of microorganisms hosted by the gastrointestinal tract are involved in numerous physiological and metabolic processes including modulation of appetite and regulation of energy in the host spanning from periphery to the brain. Indeed, bacteria and their metabolic byproducts are working in concert with the host chemosensory signaling pathways to affect both short- and long-term ingestive behavior. Sensing of nutrients and taste by specialized G protein-coupled receptor cells is important in transmitting food-related signals, optimizing nutrition as well as in prevention and treatment of several diseases, notably obesity, diabetes and associated metabolic disorders. Further, bacteria metabolites interact with specialized receptors cells expressed by gut epithelium leading to taste and appetite response changes to nutrients. This review describes recent advances on the role of gut bacteria in taste perception and functions. It further discusses how intestinal dysbiosis characteristic of several pathological conditions may alter and modulate taste preference and food consumption via changes in taste receptor expression.

Free fatty acids induce the demethylation of the fructose 1,6-biphosphatase 2 gene promoter and potentiate its expression in hepatocytes

Obesity is a serious health issue as it is a social burden and the main risk factor for other metabolic diseases. Increasing evidence indicates that a high-fat diet (HFD) is the key factor for the development of obesity, but the key genes and their associated molecular mechanisms are still not fully understood. In this study, we performed integrated bioinformatic analysis and identified that fructose-1,6 biphosphatase 2 (FBP2) was involved in free fatty acids (FFAs)-induced lipid droplet accumulation in hepatocytes and HFD-induced obesity in mice. Our data showed that palmitate (PA) and oleic acid (OA) induced the expression of FBP2 in time- and dose-dependent manners, and accelerated the development of lipid droplets in LO2 human normal liver cells. In HFD-fed C57BL/6 mice, accompanied by insulin resistance and lipid droplet accumulation, the mRNA and protein levels of FBP2 in the livers also increased significantly. The results from the methylation sequencing PCR (MSP) and bisulfite specific PCR (BSP) indicated that PA/OA induced the demethylation of the FBP2 gene promoter in LO2 cells. Moreover, betaine, a methyl donor, attenuated the expression of the FBP2 gene, the accumulation of lipid droplets, and the expression of perilipin-2, a biomarker of lipid droplets, in LO2 cells. All these findings revealed that FBP2 might be involved in HFD-induced obesity, and it is of interest to investigate the role of FBP2 in the treatment and prevention of obesity and its associated complications.

The association of fat preference with eating behavior and sex: Turkish version of the Fat Preference Questionnaire©

The fat content of food may play a role in food preferences. Increased fat intake has a role in elevated body weight. Firstly, we aimed to establish the Turkish version of the Fat Preference Questionnaire© and secondly to evaluate the relevant factors with dietary fat preference including body mass index (BMI); sex; and subscales of the Three-Factor Eating Questionnaire (TFEQ). The study was conducted with 261 participants among the academic staff of Yeditepe University. The Fat Preference Questionnaire© and TFEQ were applied. After the validity and reliability of the Turkish version of the Fat Preference Questionnaire©, Pearson's correlation coefficients were calculated to reveal the relationship between the scores of the Fat Preference Questionnaire©, BMI, and the four subscales of TFEQ. Weakly or moderately correlated variables were selected to perform two sets of hierarchical regression analyses. Turkish version of the Fat Preference Questionnaire© had statistically acceptable validity and reliability. Fat preference did not correlate with BMI (p > .05). Women showed a lower preference for high-fat foods and a higher dietary fat restriction (p < .05). The two subscales of TFEQ, the Disinhibition of Eating Control and the Susceptibility to Hunger, contributed to explain the variances in fat preference and dietary fat restriction (ΔR 2 = .04, p < .05). Fat preference correlates with Disinhibition of Eating Control and Susceptibility to Hunger, while fat restriction correlates only with Disinhibition of Eating Control although none correlates with BMI. Turkish version of the Fat Preference Questionnaire© is a valid instrument for further studies.

Orosensory Perception of Fat/Sweet Stimuli and Appetite-Regulating Peptides before and after Sleeve Gastrectomy or Gastric Bypass in Adult Women with Obesity

The aim of this study was to explore the impact of bariatric surgery on fat and sweet taste perceptions and to determine the possible correlations with gut appetite-regulating peptides and subjective food sensations. Women suffering from severe obesity (BMI > 35 kg/m2) were studied 2 weeks before and 6 months after a vertical sleeve gastrectomy (VSG, n = 32) or a Roux-en-Y gastric bypass (RYGB, n = 12). Linoleic acid (LA) and sucrose perception thresholds were determined using the three-alternative forced-choice procedure, gut hormones were assayed before and after a test meal and subjective changes in oral food sensations were self-reported using a standardized questionnaire. Despite a global positive effect of both surgeries on the reported gustatory sensations, a change in the taste sensitivity was only found after RYGB for LA. However, the fat and sweet taste perceptions were not homogenous between patients who underwent the same surgery procedure, suggesting the existence of two subgroups: patients with and without taste improvement. These gustatory changes were not correlated to the surgery-mediated modifications of the main gut appetite-regulating hormones. Collectively these data highlight the complexity of relationships between bariatric surgery and taste sensitivity and suggest that VSG and RYGB might impact the fatty taste perception differently.

Effects of Sweet-Liking on Body Composition Depend on Age and Lifestyle: A Challenge to the Simple Sweet-Liking-Obesity Hypothesis

Taste hedonics drive food choices, and food choices affect weight maintenance. Despite this, the idea that hyper-palatability of sweet foods is linked to obesity development has been controversial for decades. Here, we investigate whether interpersonal differences in sweet-liking are related to body composition. Healthy adults aged 18–34 years from the UK (n = 148) and the US (n = 126) completed laboratory-based sensory tests (sucrose taste tests) and anthropometric measures (body mass index; BMI, body fat; fat-free mass; FFM, waist/hips circumferences). Habitual beverage intake and lifestyle and behavioural characteristics were also assessed. Using hierarchical cluster analysis, we classified participants into three phenotypes: sweet liker (SL), sweet disliker (SD), and inverted-U (liking for moderate sweetness). Being a SD was linked to higher body fat among those younger than 21 years old, while in the older group, SLs had the highest BMI and FFM; age groups reflected different levels of exposure to the obesogenic environment. FFM emerged as a better predictor of sweet-liking than BMI and body fat. In the older group, sweetened beverage intake partially explained the phenotype–anthropometry associations. Collectively, our findings implicate underlying energy needs as an explanation for the variation in sweet-liking; the moderating roles of age and obesogenic environment require additional consideration.

Flavor identification inversely correlates with body mass index (BMI)

BACKGROUND AND AIMS

Dietary choices are influenced by several factors including physiological, social, or genetic factors. Among these, flavor is the most important determinant modulating food preferences. The aim of the present study was to assess flavor identification abilities in patients with obesity (Ob) in comparison with matched normal weight (NW) and over-weight (OW) subjects using a specific and validated chemosensory test.

METHODS AND RESULTS

The flavor test was administered to 140 Ob patients recruited in the obesity outpatient Unit at the Federico II University hospital and to the same number of NW and OW subjects matched by sex, age, and smoking habit. Flavor score (FS) inversely correlated with BMI. Median [Q1; Q3] FS was significantly higher in NW (14.5 [12; 16]) than in Ob (13 [10; 15] p < 0.001) and not significantly different from OW (14 [12; 16]) individuals. FS was also higher in OW than in Ob subjects (p < 0.005). When separated according to age quartiles, the BMI-related differences in FS were still significant in younger quartiles, while they were abolished in the older.

CONCLUSIONS

BMI is a critical factor modulating flavor identification, particularly in young subjects. Further investigations are needed to explore the precise mechanism and the causal relationship between body weight and olfactory dysfunctions.

CLINICALTRIAL ID

NCT03506074.

Diet-Induced Obesity Alters the Circadian Expression of Clock Genes in Mouse Gustatory Papillae

Diet-induced obesity (DIO) is associated with a defect of the orosensory detection of dietary lipids in rodents. This dysfunction is not anecdotic since it might worsen the negative effects of obesity by promoting the overconsumption of energy-dense foods. Previous studies have highlighted a progressive devaluation of reward value of lipid stimuli due to a desensitization of dopaminergic brain areas in DIO mice. Paradoxically, the putative deleterious impact of obesity on peripheral fat detection by the gustatory papillae remains poorly documented. Using a whole transcriptomic investigation of the circumvallate papillae (CVP), an analysis of CVP genes involved in fat taste transduction and signaling along the day, and two bottle choice tests, we have found that (i) CVP, known to house the most taste buds in the oral cavity, displays a genic circadian rhythm, (ii) DIO reduces the oscillation of key genes involved both in the circadian clock and lipid detection/signaling, and (iii) the gene invalidation of the clock gene Rev-Erbα does not significantly affect fat preference despite an oily solution intake slightly lower than littermate controls. Taken together these data bring the first demonstration that the gustatory function is under control of a peripheral clock in mammals, as already reported in fly and suggest that a disturbance of this rhythmicity might contribute to the lower fatty taste acuity found in obese mice.

TAS2R38 PAV Haplotype Predicts Vegetable Consumption in Community-Dwelling Caucasian Adults at Risk for Cardiovascular Disease

INTRODUCTION

A heart-healthy diet might reduce cardiovascular disease (CVD) risk. Genetic variants that affect taste are associated with food choices. This study aims to investigate the associations of the TAS2R38 haplotype with consumption of sodium, sugar, saturated fats, and vegetables.

HYPOTHESIS

We hypothesized that, compared to people who are alanine-valine-isoleucine (AVI) homozygous for the TAS2R38 gene, those who are heterozygous or homozygous for the proline-alanine-valine (PAV) haplotype would have (a) a higher intake of sodium, sugar, and saturated fat, and (b) a lower vegetable intake.

METHODS

DNA from participants at risk for CVD was genotyped, and participants were assigned to groups by haplotype. Intake for sodium, sugar, saturated fat, and vegetables was assessed using the Viocare Food Frequency Questionnaire. Intake was categorized as higher versus lower consumption, divided at the median, and examined by logistic regressions. All models controlled for age, sex, smoking status, body mass index, education level, and financial status.

RESULTS

The 175 participants had a mean age of 52 ± 13 years, 72.6% were female, 100% were Caucasian, 89.1% were overweight or obese, and 82.9% were nonsmokers. Participants with one or two PAVs were grouped together, as PAV is the dominant gene, and comprised a majority of the sample (80.6%). Haplotype did not predict intake of sodium, sugar, or saturated fats. Compared to AVI homozygotes, participants with PAV homozygous or heterozygous haplotype had lower odds of being in the higher vegetable intake group (95% CI [0.17, 0.92], p = .032).

CONCLUSIONS

PAV haplotype predicted lower consumption of vegetables. Variants of taste-related genes appear to play a role in food choices.

Cortical Response to Fat Taste

We sense fat by its texture and smell, but it is still unknown whether we also taste fat despite evidence of both candidate receptors and distinct fat taste sensations. One major reason fat is still not recognized as a basic taste quality is that we first need to demonstrate its underlying neural activity. To investigate such neural fat taste activation, we recorded evoked responses to commercial cow milk products with 0.1%, 4%, and 38 % fat via high-density electroencephalography (EEG) from 24 human participants. The experimental design ensured that the products would only be discriminable via their potential fat taste; all stimuli were carefully controlled for differences in viscosity, lubrication, odor, temperature, and confounding tastes (sweetness, acidity, and “off-taste”) and were delivered directly onto the tongue using a set of computer-controlled syringe pumps. Advanced topographical pattern analysis revealed different neural activation to the milk products 85–134 ms after stimulus onset, which, as expected, best discriminated the two milk fat extremes (0.1% and 38% fat). Notably, this time period has previously been shown to also encode basic taste qualities, such as sweet or salty. By adding to the evidence of cortical fat taste processing in response to staple food, our finding not only substantiates that we taste fat but also highlights its potential relevance during our everyday lives with possible large-scale impacts on motivational eating behavior to explain overconsumption of energy-dense foods.

A Preventive Prebiotic Supplementation Improves the Sweet Taste Perception in Diet-Induced Obese Mice

Orosensory perception of sweet stimulus is blunted in diet-induced obese (DIO) rodents. Although this alteration might contribute to unhealthy food choices, its origin remains to be understood. Cumulative evidence indicates that prebiotic manipulations of the gut microbiota are associated with changes in food intake by modulating hedonic and motivational drive for food reward. In the present study, we explore whether a prebiotic supplementation can also restore the taste sensation in DIO mice. The preference and licking behavior in response to various sucrose concentrations were determined using respectively two-bottle choice tests and gustometer analysis in lean and obese mice supplemented or not with 10% inulin-type fructans prebiotic (P) in a preventive manner. In DIO mice, P addition reduced the fat mass gain and energy intake, limited the gut dysbiosis and partially improved the sweet taste perception (rise both of sucrose preference and number of licks/10 s vs. non-supplemented DIO mice). No clear effect on orosensory perception of sucrose was found in the supplemented control mice. Therefore, a preventive P supplementation can partially correct the loss of sweet taste sensitivity found in DIO mice, with the efficiency of treatment being dependent from the nutritional status of mice (high fat diet vs. regular chow).

Cerebral gustatory activation in response to free fatty acids using gustatory evoked potentials in humans

There is some evidence of specific oro-detection of FFAs in rodents and humans. The aim of this study was to record gustatory evoked potentials (GEPs) in response to FFA solutions and to compare GEPs in response to linoleic acid solution with GEPs obtained after stimulation with sweet and salty tastants. Eighteen healthy men were randomly stimulated with fatty (linoleic acid), sweet (sucrose), and salty (NaCl) solutions at two concentrations in the first experiment. Control recordings (n = 14) were obtained during stimulation by a paraffin oil mixture without FFA or by water. In the second experiment, 28 men were randomly stimulated with five FFA solutions and a paraffin emulsion. GEPs were recorded with electroencephalographic electrodes at Cz, Fz, and Pz. GEPs were observed in response to FFA in all participants. GEP characteristics did not differ according to the quality and the concentration of the solutions in the first experiment and according to the FFA in the second experiment. This study describes for the first time GEPs in response to FFA and demonstrates that the presence of FFA in the mouth triggers an activation of the gustatory cortex. These data reinforce the concept that fat taste could be the sixth primary taste.

A New Method for Studying Licking Behavior Determinants in Rodents: Application to Diet-Induced Obese Mice

OBJECTIVE

An original device for exploring taste-guided reward behavior in rodents using a newly designed computer-controlled liquid delivery system equipped with "lickometers" is described.

METHODS

This octagonal shaped "gustometer" is composed of eight shutters that give random access during a few seconds to eight bottles delivering different liquid stimuli. This original design, which forces the animal to move for access to the drinking source, allows a simultaneous analysis of the licking behavior and motivation to drink. Determination of the sucrose licking behavior in diet-induced obese mice was used to validate this method because nutritional obesity disturbs the sweet taste perception in rodents.

RESULTS

A rise in sucrose response threshold and a decrease in the motivation to drink sweet solutions were found in mice fed the obesogenic diet. These data were highly reproducible among independent studies and corroborated the existence of functional links between diet-induced obesity and gustation in rodents.

CONCLUSIONS

The FRM-8 gustometer appears to be especially suitable for exploring determinants of behavioral outputs in response to oro-sensory stimuli in the mouse. It also provides substantial information on the taste-reward relationship, useful for better understanding the origin of gustatory efficiency or, conversely, dysfunction, as reported in nutritional obesity.

Profound differences in fat versus carbohydrate preferences in CAST/EiJ and C57BL/6J mice: Role of fat taste

In a nutrient self-selection study, CAST/EiJ mice consumed more carbohydrate than fat while C57BL/6J (B6) mice showed the opposite preference. The present study revealed similar strain differences in preferences for isocaloric fat (Intralipid) and carbohydrate (sucrose, maltodextrin) solutions in chow-fed mice. In initial 2-day choice tests, percent fat intakes of CAST and B6 mice were 4-9% and 71-81% respectively. In subsequent nutrient vs. water tests, CAST mice consumed considerably less fat but not carbohydrate compared to B6 mice. Orosensory rather than postoral factors are implicated in the very low fat preference and intake of CAST mice. This is supported by results of a choice test with Intralipid mixed with non-nutritive sweeteners vs. non-sweet maltodextrin. The preference of CAST mice for sweetened fat exceeded that of B6 mice (94 vs. 74%) and absolute fat intakes were similar in the two strains. When given unsweetened Intralipid vs. water tests at ascending fat concentrations CAST mice displayed reduced fat preferences at 0.1-5% and reduced intakes at 0.5-5% concentrations, compared to B6 mice. The differential fat preferences of CAST and B6 mice may reflect differences in fat taste sensing or in central neural processes related to fat selection.

Evaluation of association of DRD2 TaqIA and -141C InsDel polymorphisms with food intake and anthropometric data in children at the first stages of development

The reward sensation after food intake may be different between individuals and variants in genes related to the dopaminergic system may indicate a different response in people exposed to the same environmental factors. This study investigated the association of TaqIA (rs1800497) and -141C InsDel (rs1799732) variants in DRD2/ANKK1 gene with food intake and adiposity parameters in a cohort of children. The sample consisted of 270 children followed until 7 to 8 years old. DNA was extracted from blood and polymorphisms were detected by PCR-RFLP analysis. Food intake and nutritional status were compared among individuals with different SNP genotypes. Children carrying the A1 allele (TaqIA) had higher energy of lipid dense foods (LDF) when compared with A2/A2 homozygous children at 7 to 8 years old (GLM p=0.004; Mann Whitney p=0.005). No association was detected with -141C Ins/Del polymorphism. To our knowledge, this is the first association study of the DRD2 TaqIA and -141C Ins/Del polymorphism with food intake and anthropometric parameters in children. DRD2 TaqIA polymorphism has been associated with a reduction in D₂ dopamine receptor availability. Therefore, the differences observed in LDF intake in our sample may occur as an effort to compensate the hypodopaminergic functioning.

Obese Subjects With Specific Gustatory Papillae Microbiota and Salivary Cues Display an Impairment to Sense Lipids

Some obese subjects overeat lipid-rich foods. The origin of this eating behavior is unknown. We have here tested the hypothesis that these subjects could be characterized by an impaired fatty taste sensitivity linked to a change in the gustatory papillae microbial and salivary environment. The composition of microbiota and saliva surrounding the circumvallate papillae was analyzed in combination with the orosensory lipid detection threshold in normal weight (NW) and obese (O) adults. Microbial architecture was similar to what was known in feces, but with an increased frequency of Proteobacteria. No difference in the orosensory sensitivity to lipids and composition of oral microbiota and saliva was observed between NW and O subjects. By contrast, specific bacterial and salivary signatures were found in lipid non-tasters, irrespectively of BMI. A multivariate approach highlighted that the salivary flow, lysozyme activity, total antioxidant capacity and TM7 bacterial family discriminated between tasters and non-tasters. Subgroup analysis of obese tasters (OT) versus obese non-tasters (ONT) identified specific bacterial metabolic pathways (i.e. phosphotransferase and simple sugar transport systems) as being higher in ONT. Altogether with the identification of a set of significant salivary variables, our study suggests that an "obese tongue" phenotype is associated with decreased orosensory sensitivity to lipids in some obese subjects.

Tannerella forsythia and coating color on the tongue dorsum, and fatty food liking associate with fat accumulation and insulin resistance in adult catch-up fat

BACKGROUND/OBJECTIVES

We aimed to determine the alteration of Tannerella forsythia and coating color on the dorsal tongue, and fatty food liking in catch-up fat in adult (CUFA), as well as the probable associations between fat accumulation, insulin resistance (IR) and these changes.

SUBJECTS/METHODS

T. forsythia on the tongue dorsum, fatty food liking, fat accumulation and insulin sensitivity were investigated in CUFA humans and rats, and tongue-coating color was observed in CUFA individuals. We further determined the changes of fatty food liking, fat accumulation and IR in T. forsythia-infected rodents by oral lavage.

RESULTS

Increases in fat accumulation, IR, percentage of subjects with yellow tongue coating and that with T. forsythia detected were observed in CUFA individuals. Additionally, the fat ranking scores were significantly lower and the hedonic ratings of low-fat options of sampled food were lower, while the ratings of high-fat options were remarkably higher in CUFA subjects. Additionally, T. forsythia level elevated in CUFA rats, and fatty food liking, fat accumulation and IR increased in CUFA and T. forsythia-infected animals, with the increases in T. forsythia infection and fatty food liking preceding the occurrence of fat accumulation and IR.

CONCLUSIONS

T. forsythia and yellow coating on the dorsal tongue and fatty food liking associate fat accumulation and IR in CUFA. Moreover, we tentatively put forward that T. forsythia, which is very important in yellow tongue-coating microbiota, and its consequent increases in fatty food liking, might be crucial in the development of fat accumulation and IR in CUFA.

Appetite control by the tongue-gut axis and evaluation of the role of CD36/SR-B2

Understanding the mechanisms governing food intake is a public health issue given the dramatic rise of obesity over the world. The overconsumption of tasty energy-dense foods rich in lipids is considered to be one of the nutritional causes of this epidemic. Over the last decade, the identification of fatty acid receptors in strategic places in the body (i.e. oro-intestinal tract and brain) has provided a major progress in the deciphering of regulatory networks involved in the control of dietary intake. Among these lipid sensors, CD36/SR-B2 appears to play a significant role since this membrane protein, known to bind long-chain fatty acid with a high affinity, was specifically found both in enterocytes and in a subset of taste bud cells and entero-endocrine cells. After a short overview on CD36/SR-B2 structure, function and regulation, this mini-review proposes to analyze the key findings about the role of CD36/SR-B2 along of the tongue-gut axis in relation to appetite control. In addition, we discuss whether obesogenic diets might impair lipid sensing mediated by CD36/SR-B2 along this axis.

The effects of indoor and outdoor temperature on metabolic rate and adipose tissue - the Mississippi perspective on the obesity epidemic

Global warming, primarily caused by emissions of too much carbon dioxide, and climate change is a reality. This will lead to more extreme weather events with heatwaves and flooding. Some studies propose an association between thermal exposures and the prevalence of obesity with an increasing trend towards time spent in the thermal comfort zone. Longterm exposure to the thermal comfort zone can lead to a reduction of brown adipose tissue activity with an impact on energy expenditure and thermogenesis. Reduced seasonal cold exposure in combination with reduced diet-induced thermogenesis by a highly palatable high-fat and high-sugar diet and reduced physical activity contribute to the prevalence of obesity and the metabolic syndrome.