Fat taste in humans: Sources of within- and between-subject variability

Oral/taste sensitivity to non-esterified long-chain fatty acids with varying degrees of unsaturation

Understanding human oral/taste sensitivity to long-chain non-esterified fatty acids (NEFA) with varying physicochemical properties is essential to reducing the intake of fats and altering the intake composition. This study investigated the differences in human taste sensitivity to two NEFA: oleic acid and linoleic acid. Twenty-four female subjects were divided into two equal sensitivity groups, and they performed discrimination tests for both fatty acids against bottled water using either the triangle or the DR A-Not A test. To achieve an accurate measurement of NEFA sensitivity, the stimulus was carefully prepared, avoiding additives that could interfere with the binding of fatty acids to receptors. Stimuli concentrations were selected to be within the lowest range (9.9 to 177.3 μM) evaluated in previous research. Through a systematic stimulus control process, this study confirmed that greater sensitivity was exhibited to linoleic acid than oleic acid, resulting in better discrimination than previous studies.

Variability of oral/taste sensitivity to fat: An investigation of attribution from detection threshold methods with repeated measurements

Accumulating psychophysical evidence suggests substantial individual variability in oral/taste sensitivity to non-esterified, long-chain fatty acids (NEFA), which is commonly referred to as fat taste or oleogustus. Recent studies have sought to determine its associations with human factors such as body mass index (BMI) and food preferences, as it has been claimed that excessive fat consumption is related to several health conditions, including obesity. Yet, the findings are controversial. On the other hand, it has been noted that considerable variability also occurs based on the methodology used to measure the fatty acid taste. Specifically, learning effects have been observed over repeated measurements of the detection threshold of NEFA, yet there has been no methodology available to take into account these learning effects. Accordingly, in the present study, a novel methodology using a descending-block dual reminder A-Not A (DR A-Not A) method with a warm-up has been proposed to measure the NEFA detection threshold based on the signal detection theory and considering NEFA taste learning effects over repeated sessions. Homogeneous subjects (young adult Korean females within the normal BMI range, non-vegetarians) were randomized to either the novel descending-block DR A-Not A method or ascending triangle method that is commonly used for fat perception studies. Pure oleic acid emulsions were used as fat taste stimuli to be discriminated from pure mineral water. Each subject completed 14 repeated visits. For the ascending triangle method, 14 thresholds were determined using a stopping rule, while for the novel method, 7 thresholds were determined each per two consecutive days, using a criterion of a lower limit of 50% confidence interval of d' = 0.5, considering the practical aspects of taste studies in food sensory science. Based on the group median results of the last two visits, the variability of the detection thresholds was reduced using the novel descending-block DR A-Not A method due to better learning effects over repeated sessions. This shows the potential of the descending-block DR A-Not A threshold method for further studies on oral/taste sensitivity to fat.

Salt taste threshold and contributory factors of chronic kidney disease patients: a cross-sectional study

PROPOSE

High salt intake, correlated with high salt taste threshold, may accelerate renal injury in chronic kidney disease (CKD) patients. However, few studies have focused on factors that influence salt taste threshold. Therefore, we aimed to identify factors that influence the salt taste threshold of CKD patients, to provide more precise salt restriction recommendations in dietary therapy.

METHODS

Between April 2016 and March 2019, we measured the salt taste threshold of 1019 CKD patients, aged 22-78 years, from 52 hospitals across southwestern China, and then we performed a cross-sectional study.

RESULTS

The mean salt taste threshold was 0.37 ± 0.16% NaCl. There were 115 (11.3%), 670 (65.7%), and 234 (23.0%), respectively, patients who had low (≤ 0.1% NaCl), medium (0.1-0.4% NaCl), and high (> 0.4% NaCl) salt taste thresholds. One-way ANOVA and regression results revealed that sex (male), age, decreased estimated glomerular filtration rate, and absence of salt restriction were factors that influenced CKD groups with high salt taste threshold.

CONCLUSION

We found an independent correlation between contributory factors including sex, age, eGFR, and salt restriction behavior of subjects with the salt taste threshold of CKD patients. Our findings also offer insights on salt taste thresholds that could be useful for clinicians advising salt restriction to impair the salt taste sensitivity of the corresponding populations.

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.

Genetic variation in CD36 is associated with dietary intake in Korean males

Fat is one of the six types of taste. Perceived taste intensity could affect the preference for a food and whether or not it is consumed. Cluster of differentiation 36 (CD36) translocates fatty acids on the cellular membrane and is involved in the oral fat-sensing mechanism. Therefore, genetic variation rs1761667 in CD36 is known to be associated with the perception of fat taste and, hence, its dietary intake. This study examined whether CD36 rs1527479 T>C, a proxy of rs1761667, is associated with fat intake and related dietary behaviour in Koreans. Using the data of the Ansan/Ansung Study, a part of the Korean Genome Epidemiology Study, the association of rs1527479 with the intake of macronutrients, including fat and selected foods, and fat-related dietary behaviours were investigated in 3194 males and 3425 females grouped by their degree of obesity. The findings suggested that rs1527479 did not have a meaningful effect on the intake of fat or other macronutrients or on the selection of food among non-obese females and males. However, in males with obesity, the genetic variation showed a significant association with vegetable intake. Obese males with the mutant CC genotype had substantially lower cruciferous vegetable consumption (adjusted P = 0·0015) than individuals with the TT and CT genotypes. Rs1527479 had no significant effect on the frequency of consuming fried foods or commonly used types of seasoning and cooking oils. In conclusion, CD36 genetic variation was associated with the intake of cruciferous vegetables but not fat intake in obese Korean males.

Macronutrient Sensing in the Oral Cavity and Gastrointestinal Tract: Alimentary Tastes

There are numerous and diverse factors enabling the overconsumption of foods, with the sense of taste being one of these factors. There are four well established basic tastes: sweet, sour, salty, and bitter; all with perceptual independence, salience, and hedonic responses to encourage or discourage consumption. More recently, additional tastes have been added to the basic taste list including umami and fat, but they lack the perceptual independence and salience of the basics. There is also emerging evidence of taste responses to kokumi and carbohydrate. One interesting aspect is the link with the new and emerging tastes to macronutrients, with each macronutrient having two distinct perceptual qualities that, perhaps in combination, provide a holistic perception for each macronutrient: fat has fat taste and mouthfeel; protein has umami and kokumi; carbohydrate has sweet and carbohydrate tastes. These new tastes can be sensed in the oral cavity, but they have more influence post- than pre-ingestion. Umami, fat, kokumi, and carbohydrate tastes have been suggested as an independent category named alimentary. This narrative review will present and discuss evidence for macronutrient sensing throughout the alimentary canal and evidence of how each of the alimentary tastes may influence the consumption of foods.

Greater self-reported preference for fat taste and lower fat restraint are associated with more frequent intake of high-fat food

The determinants of the intake of high-fat products are not well recognized, but fat preference may be one of them. The aim of this study was thus to determine whether intake of different types of high-fat food is associated with fat preference in people with normal and increased body weight. Participants aged 20-40 years [n = 421] were enrolled in Poznań, Poland in 2016-2018. Fat preference was measured using the Fat Preference Questionnaire. Self-reported preference for fat taste (TASTE) and fat restraint (DIFF) scores were calculated. The frequency of consuming high-fat food was measured with an application for mobile devices using ecological momentary assessment. TASTE was positively associated with calorie intake and total frequency of eating high-fat food in both the normal weight and the overweight/obese groups. Overweight and obese people had lower DIFF (p < 0.001) than normal weight people. DIFF was negatively associated with total calorie intake and total intake of high-fat food, but only in normal weight people (β = -0.16, p < 0.01 and β = -0.26, p < 0.001, respectively). DIFF was negatively associated with the frequency of eating sweet (β = -0.33, p < 0.000) and meat high-fat food (β = -0.25, p < 0.001) in the normal weight group. The frequency of consumption of high-fat food and calorie intake are positively associated with self-reported preference for fat taste. In normal weight subjects fat restraint is negatively associated with calorie intake and total frequency of high-fat food intake, as well as with intake of different types of fatty food. Fat preference measures are thus associated with high-fat food intake, but these associations differ by body weight status.

Polymorphism of CD36 Determines Fat Discrimination but Not Intake of High-Fat Food in 20- to 40-Year-Old Adults

BACKGROUND

The determinants of the intake of high-fat products are not well understood.

OBJECTIVE

The aim of this study was to examine the relations between fat perception, intake of high-fat food, and body-weight status, taking into account the polymorphism of the genes that encode the proteins involved in oral fat perception.

METHODS

A total of 421 participants aged 20-40 y were enrolled in Poznań, Poland, from 2016 to 2018. An ascending forced-choice triangle procedure was applied to determine fat discrimination ability. Salad dressings with varying concentrations of canola oil were used as stimuli. Genotyping of rs1761667 (CD36) rs1573611 [free fatty acid receptor 1 (FFAR1)], rs17108973 [free fatty acid receptor 4 (FFAR4)], and rs2274333 (CA6) was performed using TaqMan probes. The frequency of consumption of high-fat foods was measured using an application for mobile devices that uses the ecological momentary assessment approach. The associations were analyzed using linear regression or logistic regression, as appropriate.

RESULTS

Individuals with the GG CD36 genotype were twice as likely to be fat discriminators, compared with the A allele carriers (P < 0.05). The mean total consumption of high-fat food was 45.8 (44.6, 47.0) times/wk and was not associated with fat discrimination or body-weight status. Obese and overweight subjects ate healthy high-fat food less frequently than did participants with normal body weight, at 4.53 (3.83, 5.23) versus 6.68 (5.82, 7.55) times/wk, respectively (P < 0.001). Men ate sweet high-fat food and snacks 15% less frequently than did women (P < 0.001 and P < 0.05) but consumed high-fat meat and fast food almost 40% more often than did women (P < 0.001 for both associations).

CONCLUSIONS

In individuals aged 20-40 y, fat discrimination ability is associated with polymorphism of CD36 but not with the choice of high-fat food. The frequency of consumption of different types of high-fat foods varies by sex and body-weight status.

Single-nucleotide polymorphism rs1761667 in the CD36 gene is associated with orosensory perception of a fatty acid in obese and normal-weight Moroccan subjects

Obese subjects have shown a preference for dietary lipids. A recent collection of evidence has proposed that a variant in the CD36 gene plays a significant role in this pathway. We assessed the association between the orosensory detection of a long-chain fatty acid, i.e. oleic acid (OA), and genetic polymorphism of the lipid taste sensor CD36 in obese and normal-weight subjects. Adult participants were recruited in the fasting condition. They were invited to fat taste perception sessions, using emulsions containing OA and according to the three-alternative forced-choice (3-AFC) method. Genomic DNA was used to determine the polymorphism (SNP rs 1761667) of the CD36 gene. Obese (n 50; BMI 34⋅97 (sd 4⋅02) kg/m²) exhibited a significantly higher oral detection threshold for OA (3⋅056 (sd 3⋅53) mmol/l) than did the normal-weight (n 50; BMI 22⋅16 (sd 1⋅81) kg/m²) participants (1⋅20 (sd 3⋅23) mmol/l; P = 0⋅007). There was a positive correlation between OA detection thresholds and BMI in all subjects; evenly with body fat percentage (BF%). AA genotype was more frequent in the obese group than normal-weight group. OA detection thresholds were much higher for AA and AG genotypes in obese subjects compared with normal-weight participants. Higher oral detection thresholds for fatty acid taste are related to BMI, BF% and not always to CD36 genotype.

GutSelf: Interindividual Variability in the Processing of Dietary Compounds by the Human Gastrointestinal Tract

Nutritional research is currently entering the field of personalized nutrition, to a large extent driven by major technological breakthroughs in analytical sciences and biocomputing. An efficient launching of the personalized approach depends on the ability of researchers to comprehensively monitor and characterize interindividual variability in the activity of the human gastrointestinal tract. This information is currently not available in such a form. This review therefore aims at identifying and discussing published data, providing evidence on interindividual variability in the processing of the major nutrients, i.e., protein, fat, carbohydrates, vitamins, and minerals, along the gastrointestinal tract, including oral processing, intestinal digestion, and absorption. Although interindividual variability is not a primary endpoint of most studies identified, a significant number of publications provides a wealth of information on this topic for each category of nutrients. This knowledge remains fragmented, however, and understanding the clinical relevance of most of the interindividual responses to food ingestion described in this review remains unclear. In that regard, this review has identified a gap and sets the base for future research addressing the issue of the interindividual variability in the response of the human organism to the ingestion of foods.

Fatty acid taste quality information via GPR120 in the anterior tongue of mice

AIM

To elucidate whether fatty acid taste has a quality that does not overlap with other primary qualities, we investigated potential neuron types coding fatty acid information and how GPR120 is involved.

METHODS

Single fibre recordings in the chorda tympani (CT) nerve and behavioural response measurements using a conditioned taste aversion paradigm were performed in GPR120-knockout (KO) and wild-type (WT) mice.

RESULTS

Single fibres can be classified into fatty acid (F)-, S-, M-, electrolyte (E)-, Q-, and N-type groups according to the maximal response among oleic acid, sucrose, monopotassium glutamate (MPG), HCl, quinine hydrochloride, and NaCl respectively. Among fibres, 4.0% in GPR120-KO and 17.9% in WT mice showed a maximal response to oleic acid (F-type). Furthermore, half or more of S- and M-type fibres showed responses to fatty acids in both mouse strains, although the thresholds in KO mice were significantly higher and impulse frequencies lower than those in WT mice. GPR120-KO mice conditioned to avoid linoleic acid showed generalized stimulus avoidances for MPG, indicating qualitative similarity between linoleic acid and MPG. The KO mice showed a higher generalization threshold for linoleic acid than that of WT mice.

CONCLUSION

Fatty acid taste is suggested to have a unique quality owing to the discovery of F-type fibres, with GPR120 involved in neural information pathways for a unique quality and palatable taste qualities in the mouse CT nerve. GPR120 plays roles in distinguishing fatty acid taste from other primary tastes and the detection of low linoleic acid concentrations.

Vitamin E Metabolic Effects and Genetic Variants: A Challenge for Precision Nutrition in Obesity and Associated Disturbances

Vitamin E (VE) has a recognized leading role as a contributor to the protection of cell constituents from oxidative damage. However, evidence suggests that the health benefits of VE go far beyond that of an antioxidant acting in lipophilic environments. In humans, VE is channeled toward pathways dealing with lipoproteins and cholesterol, underlining its relevance in lipid handling and metabolism. In this context, both VE intake and status may be relevant in physiopathological conditions associated with disturbances in lipid metabolism or concomitant with oxidative stress, such as obesity. However, dietary reference values for VE in obese populations have not yet been defined, and VE supplementation trials show contradictory results. Therefore, a better understanding of the role of genetic variants in genes involved in VE metabolism may be crucial to exert dietary recommendations with a higher degree of precision. In particular, genetic variability should be taken into account in targets concerning VE bioavailability per se or concomitant with impaired lipoprotein transport. Genetic variants associated with impaired VE liver balance, and the handling/resolution of oxidative stress might also be relevant, but the core information that exists at present is insufficient to deliver precise recommendations.

Detection thresholds for four different fatty stimuli are associated with increased dietary intake of processed high-caloric food

BMI-specific differences in food choice and energy intake have been suggested to modulate taste perception. However, associations between body composition and fat taste sensitivity are controversial. The objective of this study was to examine the association between body composition, dietary intake and detection thresholds of four fatty stimuli (oleic acid, paraffin oil, canola oil, and canola oil spiked with oleic acid) that could be perceived via gustatory and/or textural cues. In 30 participants, fat detection thresholds were determined in a repeated measurements design over twelve days. Weight status was examined by measuring the participants' BMI, waist circumference and waist-to-hip ratio. The habitual food intake was assessed via several questionnaires and twelve, non-consecutive 24-hour food diaries. In this study, a negative correlation was found between fat detection thresholds and the intake of food rich in vitamins and fibre. Moreover, a positive correlation was identified between the intake of high-fat food and fat detection thresholds. No differences in fat detection thresholds were observed due to variations in BMI or waist-to-hip ratio. These findings indicate that a regular intake of fatty foods might decrease an individuals' perceptual response to fats which might lead to excess fat intake on the long term.

Carbohydrate Taste Sensitivity Is Associated with Starch Intake and Waist Circumference in Adults

Background: Recent studies have proposed that humans may perceive complex carbohydrates and that sensitivity to simple carbohydrates is independent of sensitivity to complex carbohydrates. Variation in oral complex carbohydrate sensitivity may influence food consumption.Objective: This study aimed to investigate the associations between oral complex carbohydrate sensitivity, anthropometry, and dietary intake in adults.Methods: We assessed oral sensitivity to complex carbohydrates (maltodextrin and oligofructose) by measuring detection thresholds (DTs) and suprathreshold intensity perceptions (STs) for 34 participants, including 16 men (mean ± SEM age : 26.2 ± 0.4 y; range: 24-30 y) and 18 women (age: 29.4 ± 2.1 y; range: 24-55 y). We also measured height, weight, and waist circumference (WC) and participants completed a 4-d food diary and a food-frequency questionnaire.Results: Measurements of oral sensitivity to complex carbohydrates were significantly correlated with WC and dietary energy and starch intakes (DT: r = -0.38, P < 0.05; ST: r = 0.36-0.48, P < 0.05). When participants were grouped into tertiles, there were significant differences in WC and total energy or starch intakes for those who were more sensitive or experienced high intensity compared with those who were less sensitive or experienced low intensity. Being more sensitive or experiencing high intensity was associated with greater energy (7968-8954 kJ/d) and starch (29.1-29.8% of energy) intakes and a greater WC (88.2-91.4 cm) than was being less sensitive or experiencing low intensity (6693-7747 kJ/d, 20.9-22.2% of energy, and 75.5-80.5 cm, respectively).Conclusion: Complex carbohydrate sensing is associated with WC and consumption of complex carbohydrates and energy in adults. This trial was registered at anzctr.org.au as ACTRN12616001356459.

Taste Responses to Linoleic Acid: A Crowdsourced Population Study

Dietary fats serve multiple essential roles in human health but may also contribute to acute and chronic health complications. Thus, understanding mechanisms that influence fat ingestion are critical. All sensory systems may contribute relevant cues to fat detection, with the most recent evidence supporting a role for the sense of taste. Taste detection thresholds for fat vary markedly between individuals and responses are not normally distributed. Genetics may contribute to these observations. Using crowdsourced data obtained from families visiting the Denver Museum of Nature & Science, our objective was to estimate the heritability of fat taste (oleogustus). A pedigree analysis was conducted with 106 families (643 individuals) who rated the fat taste intensity of graded concentrations of linoleic acid (LA) embedded in taste strips. The findings estimate that 19% (P = 0.043) of the variability of taste response to LA relative to baseline is heritable at the highest concentration tested.

Fat Sensation: Fatty Acid Taste and Olfaction Sensitivity and the Link with Disinhibited Eating Behaviour

Perception of fat taste, aroma, and texture are proposed to influence food preferences, thus shaping dietary intake and eating behaviour and consequently long-term health. In this study, we investigated associations between fatty acid taste, olfaction, mouthfeel of fat, dietary intake, eating behaviour, and body mass index (BMI). Fifty women attended three sessions to assess oleic acid taste and olfaction thresholds, the olfactory threshold for n-butanol and subjective mouthfeel ratings of custard samples. Dietary intake and eating behaviour were evaluated using a Food Frequency and Three-Factor Eating Questionnaire, respectively. Binomial regression analysis was used to model fat taste and olfaction data. Taste and olfactory detection for oleic acid were positively correlated (r = 0.325; p < 0.02). Oleic acid taste hypersensitive women had significantly increased n-butanol olfactory sensitivity (p < 0.03). The eating behaviour disinhibition and BMI were higher in women who were hyposensitive to oleic acid taste (p < 0.05). Dietary intake of nuts, nut spreads, and seeds were significantly correlated with high olfactory sensitivity to oleic acid (p < 0.01). These findings demonstrate a clear link between fatty acid taste sensitivity and olfaction and suggest that fat taste perception is associated with specific characteristics of eating behaviour and body composition.

Fat Taste Sensitivity Is Associated with Short-Term and Habitual Fat Intake

Evidence suggests individuals less sensitive to fat taste (high fat taste thresholds (FTT)) may be overweight or obese and consume greater amounts of dietary fat than more sensitive individuals. The aims of this study were to assess associations between FTT, anthropometric measurements, fat intake, and liking of fatty foods. FTT was assessed in 69 Australian females (mean age 41.3 (15.6) (SD) years and mean body mass index 26.3 (5.7) kg/m²) by a 3-alternate forced choice methodology and transformed to an ordinal scale (FT rank). Food liking was assessed by hedonic ratings of high-fat and reduced-fat foods, and a 24-h food recall and food frequency questionnaire was completed. Linear mixed regression models were fitted. FT rank was associated with dietary % energy from fat ( β ^ = 0.110 [95% CI: 0.003, 0.216]), % energy from carbohydrate ( β ^ = -0.112 [-0.188, -0.035]), and frequency of consumption of foods per day from food groups: high-fat dairy ( β ^ = 1.091 [0.106, 2.242]), meat & meat alternatives ( β ^ = 0.669 [0.168, 1.170]), and grain & cereals ( β ^ = 0.771 [0.212, 1.329]) (adjusted for energy and age). There were no associations between FT rank and anthropometric measurements or hedonic ratings. Therefore, fat taste sensitivity appears to be associated with short-term fat intake, but not body size in this group of females.

The basal free fatty acid concentration in human saliva is related to salivary lipolytic activity

Fat perception during eating is a complex sensation that involves various sensory modalities, such as texture, aroma and taste. Taste is supported by the discovery of fatty acid receptors in the tongue papillae. Dietary fat is mainly composed of esterified fatty acids, whereas only free fatty acids can bind to taste receptors. Some authors have mentioned the necessity and efficiency of salivary lipolytic activity to hydrolyse the esterified fatty acids present in foods and enable fat perception. Our hypothesis is that salivary lipolytic activity is also involved in regulating the basal level of salivary fatty acids in humans. To test this hypothesis, total fatty acid (TFA) and free fatty acid (FFA) concentrations and selected salivary characteristics (such as lipolytic activity) were analysed in the resting saliva of 54 subjects. The results show differences in the TFA and FFA profiles, with TFA and FFA concentrations of 8.99 and 3.56 µg/mL of saliva, respectively. Interestingly, lipolytic activity had a significant positive correlation with FFA concentration (0.51, p < 0.01). This result highlights a possible physiological role of salivary lipolytic activity in the regulation of the basal FFA concentration. This regulation could be involved in fat taste sensitivity.

Genetics of fat intake in the determination of body mass

Body mass and fat intake are multifactorial traits that have genetic and environmental components. The gene with the greatest effect on body mass is FTO (fat mass and obesity-associated), but several studies have shown that the effect of FTO (and of other genes) on body mass can be modified by the intake of nutrients. The so-called gene–environment interactions may also be important for the effectiveness of weight-loss strategies. Food choices, and thus fat intake, depend to some extent on individual preferences. The most important biological component of food preference is taste, and the role of fat sensitivity in fat intake has recently been pointed out. Relatively few studies have analysed the genetic components of fat intake or fatty acid sensitivity in terms of their relation to obesity. It has been proposed that decreased oral fatty acid sensitivity leads to increased fat intake and thus increased body mass. One of the genes that affect fatty acid sensitivity is CD36 (cluster of differentiation 36). However, little is known so far about the genetic component of fat sensing. We performed a literature review to identify the state of knowledge regarding the genetics of fat intake and its relation to body-mass determination, and to identify the priorities for further investigations.

Comparisons of Fatty Acid Taste Detection Thresholds in People Who Are Lean vs. Overweight or Obese: A Systematic Review and Meta-Analysis

Given the increasing evidence that supports the ability of humans to taste non-esterified fatty acids (NEFA), recent studies have sought to determine if relationships exist between oral sensitivity to NEFA (measured as thresholds), food intake and obesity. Published findings suggest there is either no association or an inverse association. A systematic review and meta-analysis was conducted to determine if differences in fatty acid taste sensitivity or intensity ratings exist between individuals who are lean or obese. A total of 7 studies that reported measurement of taste sensations to non-esterified fatty acids by psychophysical methods (e.g.,studies using model systems rather than foods, detection thresholds as measured by a 3-alternative forced choice ascending methodology were included in the meta-analysis. Two other studies that measured intensity ratings to graded suprathreshold NEFA concentrations were evaluated qualitatively. No significant differences in fatty acid taste thresholds or intensity were observed. Thus, differences in fatty acid taste sensitivity do not appear to precede or result from obesity.

Consumer Acceptability of Intramuscular Fat

Fat in meat greatly improves eating quality, yet many consumers avoid visible fat, mainly because of health concerns. Generations of consumers, especially in the English-speaking world, have been convinced by health authorities that animal fat, particularly saturated or solid fat, should be reduced or avoided to maintain a healthy diet. Decades of negative messages regarding animal fats has resulted in general avoidance of fatty cuts of meat. Paradoxically, low fat or lean meat tends to have poor eating quality and flavor and low consumer acceptability. The failure of low-fat high-carbohydrate diets to curb "globesity" has prompted many experts to re-evaluate of the place of fat in human diets, including animal fat. Attitudes towards fat vary dramatically between and within cultures. Previous generations of humans sought out fatty cuts of meat for their superior sensory properties. Many consumers in East and Southeast Asia have traditionally valued more fatty meat cuts. As nutritional messages around dietary fat change, there is evidence that attitudes towards animal fat are changing and many consumers are rediscovering and embracing fattier cuts of meat, including marbled beef. The present work provides a short overview of the unique sensory characteristics of marbled beef and changing consumer preferences for fat in meat in general.

The influence of a high-fat meal on fat taste thresholds

A high-fat diet for four weeks has been shown to attenuate fat taste sensitivity in healthy weight individuals. However, there is minimal evidence as to whether a single high-fat meal immediately prior to fat taste threshold testing has an effect on thresholds. Therefore, the aim of the study was to determine the effect of a high-fat meal immediately prior to detection threshold testing for oleic acid (C18:1). Thirty-two participants (15 males, 17 females, aged 39.1 ± 3.1 years, Body Mass Index 23.1 ± 0.7 kg/m(2)) attended three laboratory sessions. In each session, participants were randomly assigned to one of three different types of breakfast: a high-fat (60% energy from fat), or low-fat (20% energy from fat) or macronutrient balanced (33% energy from fat) frittata. Fat taste thresholds were evaluated using ascending forced choice triangle tests on two occasions each day; once one-hour post breakfast and then one-hour post the completion of the first threshold test. There was no effect of breakfast type on fat taste detection thresholds for the first testing session of each day (P = 0.288), or the second testing session of each day (P = 0.754). There was also no effect of breakfast within each day (day 1: P = 0.198, day 2: P = 0.199, day 3: P = 0.125). There was no effect of macronutrient composition on the ability of participants to rank the level of fat in food (P = 0.345), or preference for the level of fat in food (P = 0.187-0.868). This study provides preliminary evidence that the composition of the meal consumed by a participant immediately prior to testing does not affect fat taste thresholds.

Controversies in fat perception

Nutritional fat is one of the most controversial topics in nutritional research, particularly against the background of obesity. Studies investigating fat taste perception have revealed several associations with sensory, genetic, and personal factors (e.g. BMI). However, neuronal activation patterns, which are known to be highly sensitive to different tastes as well as to BMI differences, have not yet been included in the scheme of fat taste perception. We will therefore provide a comprehensive survey of the sensory, genetic, and personal factors associated with fat taste perception and highlight the benefits of applying neuroimaging research. We will also give a critical overview of studies investigating sensory fat perception and the challenges resulting from multifaceted methodological approaches. In conclusion, we will discuss a multifactorial approach to fat perception to gain a better understanding of the underlying mechanisms that cause varying fat sensitivity which could be responsible for overeating. Such knowledge might be beneficial in new treatment strategies for obesity and overweight.

No Difference in Perceived Intensity of Linoleic Acid in the Oral Cavity between Obese and Nonobese Individuals

Findings from studies examining interactions between fat taste and dietary fat intake or body weight are mixed. A convenience sample of 735 visitors to the Denver Museum of Nature & Science ≥8 years old rated the taste intensity of edible taste strips impregnated with varying concentrations (%v/v) of linoleic acid (LA) (blank = 0.0, low = 0.06, medium = 0.15, high = 0.38). Percent body fat (BF%) was measured using bioelectrical impedance. Fat taste intensity was rated as significantly different across all concentrations (P < 0.001) except between the blank and low concentrations (P = 0.1). Ratings increased monotonically across concentrations. Children (<18 years; N = 180) rated all concentrations as more intense than adults (P < 0.001 for all). Women and girls rated the highest concentration as more intense than men and boys (P < 0.02 for all). BF% was not correlated with fat taste intensity ratings. Self-reported dietary intake indicated that obese individuals’ intensity ratings for medium and high concentrations of LA were inversely related to recent mono- and poly-unsaturated fat exposure (r = −0.19 to −0.27; P < 0.03 for all). No such associations were observed in the nonobese group. Findings suggest that factors other than simple adiposity status influence fat taste intensity ratings, and that participants in fat taste studies should receive standardized meals prior to testing.

Recent advances in fatty acid perception and genetics

This article summarizes new knowledge about the contribution of genetic variation to person-to-person differences underlying some sensory aspects of dietary fatty acids. Receptors on the taste cells of the human tongue arise from genes that have marked variation in DNA sequence, which, in some cases, is associated with differences in how these lipids in foods are perceived. These perceptual differences may affect food selection.

The A allele of cluster of differentiation 36 (CD36) SNP 1761667 associates with decreased lipid taste perception in obese Tunisian women

Recent studies have suggested that excessive intake of dietary fat is associated with obesity. Some obese subjects have been reported to exhibit high thresholds for the gustatory detection of lipids via lipid receptors, such as cluster of differentiation 36 (CD36). We studied lingual detection thresholds for emulsions containing oleic acid in obese Tunisian women (n 203) using a three-alternative forced choice (3-AFC) method. Genotyping of the TNF-α (rs1800629), IL-6 (rs1800795) and CD36 (rs1761667) genes was performed to associate with lipid taste perception thresholds. The CD36 genotype distribution was as follows: GG (n 42), AG (n 102) and AA (n 59). Women with the CD36 GG genotype exhibited oral detection thresholds for oleic acid that were more than three times lower than those with the CD36 AA genotype. The present study confirms a high threshold of gustatory fat detection in obese women with the CD36 AA genotype, but there is no significant association with the IL-6 and TNF-α gene polymorphisms.

Humans are more sensitive to the taste of linoleic and α-linolenic than oleic acid

Health concerns have led to recommendations to replace saturated fats with unsaturated fats. However, addition of unsaturated fatty acids may lead to changes in the way foods are perceived in the oral cavity. This study tested the taste sensitivity to and emulsion characteristics of oleic, linoleic, and α-linolenic acids. The hypothesis tested was that oral sensitivity to nonesterified fatty acids would increase with degree of unsaturation but that in vitro viscosities and particle sizes of these emulsions would not differ. Oral taste thresholds were obtained using the three-alternative, forced-choice, ascending method. Each participant was tested on each fat 7 times, for a total of 21 study visits, to account for learning effects. Viscosities were obtained for the blank solutions and all three emulsions. Results indicate lower oral thresholds to linoleic and α-linolenic than oleic acid. At higher shear rates, 5% oleic and linoleic acid were more viscous than other samples. More-dilute emulsions showed no significant differences in viscosity. Particle sizes of the emulsions increased very slightly with increasing unsaturation. Together, the emulsion characteristics and oral sensitivity data support a taste mechanism for nonesterified fatty acid detection.

Genetic sensitivity to the bitter taste of 6-n-propylthiouracil (PROP) and its association with physiological mechanisms controlling body mass index (BMI)

Taste sensitivity to the bitter compound 6-n-propylthiouracil (PROP) is considered a marker for individual differences in taste perception that may influence food preferences and eating behavior, and thereby energy metabolism. This review describes genetic factors that may contribute to PROP sensitivity including: (1) the variants of the TAS2R38 bitter receptor with their different affinities for the stimulus; (2) the gene that controls the gustin protein that acts as a salivary trophic factor for fungiform taste papillae; and (3) other specific salivary proteins that could be involved in facilitating the binding of the PROP molecule with its receptor. In addition, we speculate on the influence of taste sensitivity on energy metabolism, possibly via modulation of the endocannabinoid system, and its possible role in regulating body composition homeostasis.

Different oral sensitivities to and sensations of short-, medium-, and long-chain fatty acids in humans

Fatty acids that vary in chain length and degree of unsaturation have different effects on metabolism and human health. As evidence for a "taste" of nonesterified fatty acids (NEFA) accumulates, it may be hypothesized that fatty acid structures will also influence oral sensations. The present study examined oral sensitivity to caproic (C6), lauric (C12), and oleic (C18:1) acids over repeated visits. Analyses were also conducted on textural properties of NEFA emulsions and blank solutions. Oral thresholds for caproic acid were lower compared with oleic acid. Lauric acid thresholds were intermediate but not significantly different from either, likely due to lingering irritating sensations that prevented accurate discrimination. From particle size analysis, larger droplets were observed in blank solutions when mineral oil was used, leading to instability of the emulsion, which was not observed when emulsions contained NEFA or when mineral oil was removed from the blank. Rheological data showed no differences in viscosity among samples except for a slightly higher viscosity with oleic acid concentrations above 58 mM. Thus, texture was unlikely to be the property used to distinguish between the samples. Differences in oral detection and sensation of caproic, lauric, and oleic acids may be due to different properties of the fatty acid alkyl chains.

Measuring oral fatty acid thresholds, fat perception, fatty food liking, and papillae density in humans

Emerging evidence from a number of laboratories indicates that humans have the ability to identify fatty acids in the oral cavity, presumably via fatty acid receptors housed on taste cells. Previous research has shown that an individual's oral sensitivity to fatty acid, specifically oleic acid (C18:1) is associated with body mass index (BMI), dietary fat consumption, and the ability to identify fat in foods. We have developed a reliable and reproducible method to assess oral chemoreception of fatty acids, using a milk and C18:1 emulsion, together with an ascending forced choice triangle procedure. In parallel, a food matrix has been developed to assess an individual's ability to perceive fat, in addition to a simple method to assess fatty food liking. As an added measure tongue photography is used to assess papillae density, with higher density often being associated with increased taste sensitivity.

Obesity interferes with the orosensory detection of long-chain fatty acids in humans

BACKGROUND

The association between the orosensory detection of lipids, preference for fatty foods, and body mass index (BMI; in kg/m(2)) is controversial in humans.

OBJECTIVE

We explored the oral lipid-sensing system and the orosensory-induced autonomic reflex system in lean and obese subjects.

DESIGN

Lean (BMI: 19 to <25; n = 30) and obese (BMI >30; n = 29) age-matched men were enrolled. Their oral threshold sensitivity to linoleic acid (LA) was determined by using a 3-alternative forced-choice ascending procedure, and their eating habits were established by the analysis of 4 consecutive 24-h food-consumption diaries. The effect of brief oral lipid stimulations on plasma triglyceride [(TG)pl] concentrations was analyzed in overnight-fasted lean and obese individuals subjected to a whole-mouth stimulation (sip-and-spit procedure) with a control or 1% LA emulsions for 5 min according to a within-subject randomized design.

RESULTS

A large distribution of LA detection was shown in both groups. Mean detection thresholds were 0.053% (wt:wt) and 0.071% (wt:wt) in lean and obese subjects, respectively. No relation between the LA detection threshold and BMI was observed. The 5 subjects who detected only the higher concentration of LA (5% wt:wt) or were unable to distinguish properly between control and LA emulsions were obese. An analysis of dietary habits showed that these obese LA nontasters consumed more lipids and energy than did all other subjects. Brief whole-mouth stimulations (sip-and-spit procedure) with a control or 1% LA emulsion revealed an LA-mediated rise in (TG)pl concentrations in overnight-fasted, lean subjects. The origin of this change seemed to be hepatic. This (TG)pl upregulation was not shown in obese subjects, which suggested that obesity led to disturbances in the oral-brainstem-periphery loop.

CONCLUSION

Altogether, these data strongly suggest that obesity may interfere with the orosensory system responsible for the detection of free long-chain fatty acids in humans. This trial was registered at clinicaltrials.gov as NCT02028975.

Cell signaling mechanisms of oro-gustatory detection of dietary fat: advances and challenges

CD36 and two G-protein coupled receptors (GPCR), i.e., GPR120 and GPR40, have been implicated in the gustatory perception of dietary fats in rodents. These glycoproteins are coupled to increases in free intracellular Ca²⁺ concentrations, [Ca²⁺](i), during their activation by dietary long-chain fatty acids (LCFA). The transient receptor potential type M5 (TRPM5) channel, activated by [Ca²⁺](i), participates in downstream signaling in taste bud cells (TBC). The mice, knocked-out for expression of CD36, GPR120, GPR40 or TRPM5 have a reduced spontaneous preference for fat. The delayed rectifying K⁺ (DRK) channels believed to lie downstream of these receptors are also important players in fat taste transduction. The trigeminal neurons by triggering increases in [Ca²⁺](i) may influence the taste signal to afferent nerve fibers. Why are there so many taste receptor candidates for one taste modality? We discuss the recent advances on the role of CD36, GPR120, GPR40, TRPM5 and DRK channels, in signal transduction in TBC. We shed light on their cross-talk and delineate their roles in obesity as a better understanding of the molecular mechanisms behind their regulation could eventually lead to new strategies to fight against this condition.

Ciclopirox olamine lotion 1%: bioequivalence to ciclopirox olamine cream 1% and clinical efficacy in tinea pedis

Studies were conducted to assess the bioequivalence of a new antimycotic formulation, ciclopirox olamine lotion 1%, to an established compound, ciclopirox olamine cream 1%. Results of in vitro studies, using skin samples from human cadavers and domestic pigs, demonstrated that the two formulations equally penetrate all layers of the stratum corneum and inhibit the growth of Trichophyton mentagrophytes and Candida albicans. In vivo studies in guinea pigs and in human volunteers demonstrated the comparable therapeutic efficacy of the lotion and the cream in experimental trichophytosis. In addition, a multicenter, double-blind clinical trial was undertaken to compare ciclopirox olamine lotion 1% with the vehicle alone in the treatment of patients with tinea pedis. Patients with plantar, interdigital, or vesicular tinea pedis were enrolled in the studies. Patients were treated for 28 days. Clinical and mycological responses were determined during treatment and two weeks posttreatment. Ciclopirox olamine lotion 1% was found to be significantly more effective than its vehicle in the treatment of patients with common tinea pedis. Minor localized side effects (pruritus, burning sensation) were reported in 2% of 89 patients treated with ciclopirox olamine lotion 1%. The results demonstrate the bioequivalence of ciclopirox olamine lotion 1% and ciclopirox olamine cream 1% and confirm the clinical effectiveness and safety of the lotion in the treatment of tinea pedis, a generally recalcitrant fungal infection. It is concluded that ciclopirox olamine lotion 1% can be used as an alternative to ciclopirox olamine cream 1% for treatment of tinea pedis, tinea versicolor, tinea cruris, tinea corporis, and cutaneous candidiasis when the convenience and/or cosmetic elegance of a lotion is desired.