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. A major contributor to cardiovascular disease is a diet high in saturated fatty acids (33). Replacement of saturated fatty acid with mono- or polyunsaturated fatty acids (MUFA or PUFA, respectively) may improve blood lipid profiles, decrease markers for cardiovascular disease, and improve insulin responses in insulin-resistant or type 2 diabetic patients (34, 35). Thus the type of dietary fatty acids should be a critical consideration in evaluation of the healthfulness of high-fat foods. Oleic, linoleic, and α-linolenic acids are unsaturated fatty acids with one, two, and three double bonds, respectively. Oleic and linoleic acids are common in liquid vegetable oils, such as safflower, canola, and olive oils, while α-linolenic acid is predominantly found in fish oil. The PUFAs, linoleic and α-linolenic acids, are ω-6 and ω-3 fatty acids, respectively, and humans lack endogenous desaturases to create the double bonds at these positions of the alkyl chain. Thus these fatty acids are considered essential fatty acids and must be obtained from the diet. As different molecular structures of fatty acids influence health outcomes, structural differences could also influence affinity for various receptors, including proposed fatty acid taste receptors in the human mouth, as demonstrated for G protein-coupled receptor (GPR) 120 (4, 10, 12). While dietary fat, primarily present as triacylglycerol, has traditionally been valued for textural contributions to food, evidence indicates that nonesterified fatty acids (NEFA) are effective taste stimuli in the oral cavity (11, 20, 32). Large variability has been observed in NEFA oral sensitivity, which can be modified by dietary fat intake or by weight status (20, 23–26). However, most of the human work has tested only oleic acid. New data obtained through improved techniques and multiple tests per NEFA indicate that human oral sensitivity to varying NEFA differs according to properties of the alkyl chain (19). The current study is designed to evaluate differences in human sensitivity to NEFA that vary in degree of unsaturation, but not chain length. Previous studies have observed lower oral thresholds for linoleic than oleic acid (23) or no difference between these two fatty acids (5). Data from another report show a lower oral fatty taste threshold for α-linolenic than linoleic acid, which is, in turn, lower than that for oleic acid, but means and standard deviations to test for significant differences were not reported (10). Notably, none of these previous reports tested individuals multiple times with individual NEFA. Data published on oleic acid indicate that individuals may learn the taste of oleic acid over multiple tests, leading to lower thresholds in later visits than in the first test (29, 31). While learning effects are not always observed or may be blunted by using nonnaive participants (19), multiple visits should be conducted because of the high variability of sensory threshold data and the high occurrence of false positives, which would artificially lower threshold values (18). Thus the present study was designed to observe not only whether oral sensitivity to NEFA increases with greater unsaturation of the alkyl chain, but also whether multiple tests would give more consistent data on this relationship. Our hypotheses were as follows: 1) humans would be most sensitive to the taste of α-linolenic acid, followed by linoleic acid and then oleic acid, and 2) learning effects would be observed over multiple tests, particularly in naive participants. We expected these learning effects to attenuate over the course of the 21 visits (7 visits per NEFA) conducted in the study. Because of ongoing concerns of controlling for emulsion texture in NEFA taste experiments, data on particle size distributions and rheology of the samples were also collected and analyzed. We hypothesized that there would be no difference in particle size among the emulsions of different NEFA and that viscosity would be similar among the emulsions and the blank solutions

Effects of Peanut Processing on Masticatory Performance during Variable Appetitive States

Background. Current evidence indicates that peanut consumption reduces cardiovascular disease risk, while posing little threat to positive energy balance. However, questions have been raised as to whether inter- and intraindividual variability in mastication in response to peanut form and processing properties may influence these health effects, since mastication has the potential to alter the bioaccessibility of nutrients within the nut matrix. Objective. To explore the relationship between peanut form and processing and masticatory function. Subjects/Methods. Thirty nine adults (16 M, 23 F; BMI: 30.4 ± 4.0 kg/m2; age: 27 ± 8 y) with healthy dentition chewed four different forms of peanuts until they would normally swallow and then expectorated the bolus. Surface electromyograms (EMGs) were obtained from the masseter and temporalis muscles during chewing of the four test foods. The maximum and mean bite forces, duration of chewing sequence, number of chews, and total muscle work for the complete chewing cycle were measured on the integrated EMG in fasted and sated states. Results. While no significant differences were noted in response to appetitive state, peanut form and processing had a significant influence on masticatory efficiency, as measured by proportional particle size distributions. The processed peanuts (honey roasted, roasted salted, and roasted unsalted) were chewed significantly fewer times compared to the unprocessed form (raw). Further, the proportional particle sizes within the swallowing bolus were significantly larger for the processed forms compared to the unprocessed form. Conclusion. These observations may have implications for bioaccessibility of energy and cardioprotective nutrients as well as endocrine responses, following peanut consumption

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. structural features of fatty acids, predominantly chain length and degree of unsaturation, determine their physiological role in preventing, promoting, or alleviating disease states (3, 16, 29, 42). Generally, polyunsaturated fatty acids and cis-monounsaturated fatty acids are associated with improved health outcomes when substituted for saturated fatty acids (3, 16, 29, 42). Chemically, unsaturation and shorter chain length lead to faster diffusion through cell membranes (30), and long-chain polyunsaturated fatty acids have greater affinity for certain fatty acid receptors, such as G protein-coupled receptor (GPR)120, than saturated or short-chain fatty acids (18, 27). Definitions of “short-chain,” “medium-chain,” and “long-chain” fatty acids vary, but generally short-chain fatty acids are composed of 2 to 4, and sometimes up to 6, carbons, medium-chain fatty acids are composed of 6 or 8 to 10 or 12 carbons, and long-chain fatty acids are composed of 12 or 14 to longer carbon chains. As the alkyl chain length increases, the molecules become less water soluble. Short- and medium-chain fatty acids also diffuse more rapidly across cell membranes than long-chain fatty acids (17). Short-chain fatty acids, such as butyric (C4) and caproic (C6) acids, are present in dairy products, but the bulk of these fatty acids in the human diet are actually byproducts of dietary fiber fermentation by bacteria in the colon (11, 12, 26, 65, 66). Medium-chain fatty acids of 8–12 carbons are found in foods such as palm kernel oil and coconut oil, with some lower concentrations in dairy products (1). Long-chain fatty acids are the most abundant fatty acids in the human diet, as they are prevalent in most triglycerides in food and are vital components of cell membranes. Knowing that structural differences influence the absorption (38) and physiological roles of fatty acids in nongustatory tissues, and given the accumulated evidence that nonesterified fatty acids (NEFA) are effective taste stimuli in humans and rodents (for recent reviews, see Refs. 20, 39, 44, and 59), the concept that structure may alter the taste sensation of NEFA seems probable. While numerous studies have been conducted to investigate the role of different types of NEFA on health outcomes, few have investigated their differential impacts on oral chemosensation in humans. One study (51) showed lower thresholds for linoleic (C18:2) than oleic (C18:2) or lauric (C12) acids, whereas another study (36) showed no differences in thresholds for caproic (C6), lauric, and stearic (C18) acids. Additional studies have reported caproic acid thresholds are lower than linoleic, stearic, and lauric acid thresholds (35) and no difference in sensitivity among oleic, linoleic, and stearic acids (8). However, all of these studies only tested each participant once. New research has shown wide within-subject variability and/or learning effects over time, indicating a need for multiple testing visits to establish reliable taste thresholds for these compounds (57, 58). A study (18) that used a trained panel, who presumably had numerous exposures to the NEFA, tested a variety of NEFA (C10, C12, C18:1, C18:2, C18:3, and C20:4), but that report did not indicate whether the thresholds differed significantly. Thus, clarification is needed for whether oral sensitivity to NEFA differ by fatty acid structure and whether multiple tests per participant are required to document accurate limits of detection for each NEFA (57, 58). Additionally, most NEFA taste studies have used carbohydrate gums and/or mineral oil to mask the textural contribution of NEFA to the blank sample (for a review, see Ref. 44). Textural properties and physical characteristics, such as particle size and emulsion stability, of NEFA emulsions are rarely reported, yet such parameters contribute to the oral sensation of emulsions (13–15, 49, 62, 64). While there is evidence that carbohydrate thickeners mitigate the increase in perceived thickness caused by unstable emulsions (64), the efficacy of mineral oil as a textural masking agent for NEFA has not been studied. Given that mineral oil, unlike NEFA, contains no hydrophilic moieties, this lipid does not form natural micelles. Thus, the physical structure formed in a mineral oil emulsion is different from an emulsion containing NEFA. We thus tested emulsions of NEFA with and without mineral oil as well as “blank” solutions of carbohydrate gums with and without mineral oil to determine what physical effects this lipid has on the samples. The present study was designed to investigate the differences in oral taste thresholds of caproic (hexanoic, C6), lauric (dodecanoic, C12), and oleic (cis-9-octadecenoic, C18:1) acids as well as assess the potential differences in viscosity and particle size for NEFA emulsions with or without mineral oil. The stimuli examined here were 6, 12, and 18 carbon fatty acids and are referred to as short-, medium-, and long-chain fatty acids. While stearic acid would have been a more ideal candidate to maintain the same level of saturation among the tested NEFA, stearic acid is solid until 69°C, a temperature at which sustained exposure could cause thermal burns. The hypotheses tested were 1) emulsion particle sizes would be smaller for mixtures with NEFA than mixtures with mineral oil alone, 2) viscosity would be greater for emulsions containing mineral oil than emulsions not containing mineral oil, 3) viscosity would not be significantly different among NEFA emulsions and the blank, 4) human oral sensitivity to NEFA would increase with decreasing alkyl chain length (sensitivity to caproic acid \u3e lauric acid \u3e oleic acid), and 5) human oral sensitivity to all NEFA would improve over multiple testing sessions

Comparison of sensory, physiological, personality, and cultural attributes in regular spicy food users and non-users

Some individuals savor spicy foods, while others avoid them. Reasons underlying this range of hedonic responses are unknown. The purpose of this study was to explore the basis for individual differences in preference for spicy foods. Regular spicy food users ( n= 13) and non-users (n= 12) were characterized for selected sensory, physiological, personality, and cultural attributes. Individual differences between users and non-users were primarily related to sensory and cultural attributes (i.e., a higher proportion of users reported consuming spicy foods since childhood and users rated spicy foods as more palatable and were better able to discriminate this burn than non-users). Users and non-users exhibited comparable responsiveness to noxious pressure pain, oral tactile sensitivity, and auditory sensitivity, varying only in responsiveness to oral thermal heat (i.e., users were more sensitive to increases than non-users). Studied personality traits did not vary between users and non-users. These findings suggest that prior experience, rather than physiological adaptation or personality differences, may best predict preference for spicy foods. These findings are of public health interest, given that spicy food consumption is reported to confer weight management and food safety benefits

Noxious stimuli sensitivity in regular spicy food users and non-users: Comparison of visual analog and general labeled magnitude scaling

The visual analog scale (VAS) and the general labeled magnitude scale (gLMS) are common response formats for assessing chemosensory sensation. The gLMS is recommended when comparing sensations between individuals whose perceptual experiences vary in a manner that may not be accurately captured on the VAS. This may occur when one group has a wider range of perceived intensity (e.g., bitterness in 6-n-propylthiouracil (PROP) tasters and non-tasters). The purpose of this study was to compare responses generated by the VAS and the gLMS following exposure to chemical, thermal, tactile, and auditory stimuli at intensity levels encountered in daily activities. Subjects were 25 healthy, lean men and women (13 regular spicy food users and 12 non-users). PROP taster prevalence was equal among regular spicy food users and non-users. Replicating a well-documented phenomenon, the slope of the function describing the growth of sensation with stimulus strength was greater for PROP in tasters than non-tasters (41.4% and 7.6% gLMS usage, respectively). The slope was greater with the VAS compared to the gLMS for all other noxious stimuli (50.1% and 29.3% scale usage, respectively). However, the slopes of both scales were moderately to highly correlated both within (all subjects) and between groups (users versus non-users and men versus women; most \u3e0.65). These findings suggest that scale selection is context-dependent. While the VAS and the gLMS generated similar results after exposure to potentially noxious stimuli at concentrations likely to be experienced in daily life, the gLMS is more appropriate when ratings of stimuli perceived as extreme are expected

Oleogustus: The Unique Taste of Fat

Considerable mechanistic data indicate there may be a sixth basic taste: fat. However, evidence demonstrating that the sensation of non-esterified fatty acids (the proposed stimuli for “fat taste”) differs qualitatively from other tastes is lacking. Using perceptual mapping, we demonstrate that medium and long-chain non-esterified fatty acids have a taste sensation that is distinct from other basic tastes (sweet, sour, salty, and bitter). While some overlap was observed between these NEFA and umami taste, this overlap is likely due to unfamiliarity with umami sensations rather than true similarity. Shorter chain fatty acids stimulate a sensation similar to sour, but as chain length increases this sensation changes. Fat taste oral signaling, and the different signals caused by different alkyl chain lengths, may hold implications for food product development, clinical practice, and public health policy

Post‐Exercise Substrate Utilization after a High Glucose vs. High Fructose Meal During Negative Energy Balance in the Obese

Objective: To assess the effects of negative energy balance on the metabolic response of a meal containing either glucose or fructose as the primary source of carbohydrate after exercise in obese individuals in energy balance, or negative energy balance. Research Methods and Procedures: Fourteen adults with mean body mass index (BMI) 30.3 ± 1 kg/m2, age 26 ± 2 years, and weight 93.5 ± 5.4 kg, adhered to an energy‐balanced (EB) or a negative energy‐balanced (NEB) diet for 6 days. On Day 7, subjects exercised at 70% VO2peak for 40 minutes then consumed either high glucose (50 g of glucose, HG) or high fructose (50 g of fructose, HF) liquid meal. Substrate utilization was measured by indirect calorimetry for 3 hours. Blood samples were collected before exercise and 0, 30, 60, 120, and 180 minutes after consuming the meal. Results: The HG produced 15.9% greater glycemic (p \u3c 0.05) and 30.9% larger insulinemic (p \u3c 0.05) responses than the HF under both EB and NEB conditions. After the NEB diet, carbohydrate and fat oxidation did not differ for HG and HF. In contrast, carbohydrate oxidation increased 31%, and fat oxidation decreased 39% with HF compared with HG after the EB diet. Thus, HF and HG consumed after exercise produced marked differences in macronutrient oxidation when obese subjects followed an EB diet, but no difference when adhering to a NEB diet. Discussion: The data suggest that the use of fructose in supplements/meals may provide no additional benefit in terms of substrate utilization during a weight loss program involving diet and exercise

Mastication of Nuts under Realistic Eating Conditions: Implications for Energy Balance

The low digestibility and high satiety effects of nuts have been partly attributed to mastication. This work examines chewing forces and the bolus particle size of nuts (walnuts, almonds, pistachios) varying in physical properties under different conditions (with and without water, juice, sweetened yogurt and plain yogurt) along with satiety sensations and gut hormone concentrations following walnut consumption (whole or butter). In a randomized, cross-over design with 50 adults (25 males, 25 females; Body Mass Index (BMI) 24.7 ± 3.4 kg/m²; age: 18⁻52 years old (y/o), the chewing forces and particle size distribution of chewed nuts were measured under different chewing conditions. Appetite sensations were measured at regular intervals for 3 h after nut intake, and plasma samples were collected for the measurement of glucose, insulin and Glucagon-like peptide-1 (GLP-1). The three nuts displayed different particle sizes at swallowing though no differences in chewing forces were observed. Walnuts with yogurt yielded larger particle sizes than the other treatments. Particle size was not correlated with either food palatability or flavor. Fullness sensations were higher after whole nut than nut butter consumption though there were no significant changes in glucose, insulin, or GLP-1 concentrations under any condition. Changing the conditions at swallowing might influence the release of energy from nuts

Acute and second-meal effects of almond form in impaired glucose tolerant adults: a randomized crossover trial

<p>Abstract</p> <p>Background</p> <p>Nut consumption may reduce the risk of developing type 2 diabetes. The aim of the current study was to measure the acute and second-meal effects of morning almond consumption and determine the contribution of different nut fractions.</p> <p>Methods</p> <p>Fourteen impaired glucose tolerant (IGT) adults participated in a randomized, 5-arm, crossover design study where whole almonds (WA), almond butter (AB), defatted almond flour (AF), almond oil (AO) or no almonds (vehicle - V) were incorporated into a 75 g available carbohydrate-matched breakfast meal. Postprandial concentrations of blood glucose, insulin, non-esterified free fatty acids (NEFA), glucagon-like peptide-1 (GLP-1) and appetitive sensations were assessed after treatment breakfasts and a standard lunch.</p> <p>Results</p> <p>WA significantly attenuated second-meal and daylong blood glucose incremental area under the curve (AUCI) and provided the greatest daylong feeling of fullness. AB and AO decreased blood glucose AUCI in the morning period and daylong blood glucose AUCI was attenuated with AO. WA and AO elicited a greater second-meal insulin response, particularly in the early postprandial phase, and concurrently suppressed the second-meal NEFA response. GLP-1 concentrations did not vary significantly between treatments.</p> <p>Conclusions</p> <p>Inclusion of almonds in the breakfast meal decreased blood glucose concentrations and increased satiety both acutely and after a second-meal in adults with IGT. The lipid component of almonds is likely responsible for the immediate post-ingestive response, although it cannot explain the differential second-meal response to AB versus WA and AO.</p