Robin M. Tucker

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

Non-esterified fatty acids (NEFA) are reportedly detectable through taste mechanisms in the human oral cavity. However, wide variability has been observed in NEFA taste sensitivity between and within subjects as well as across research groups. Some of this variability may be due to the hydrophobic nature of the NEFA and the methods used to make stimuli emulsions. As NEFA are poorly soluble in water, emulsification is necessary for delivery of stimuli to taste receptors. However, properties of emulsions may also be detected by somatosensory cues complicating attribution of sensory findings to taste. Additionally, learning (improved test performance) has been observed when using traditional tests for measuring sensitivity to NEFA, which may contribute greatly to within-subject variability if not standardized. Factors such as sex, diet, and BMI have been proposed to affect NEFA taste sensitivity, but the degree to which these individual factors influence NEFA detection thresholds remains to be fully established. Improved knowledge of stimulus properties and individual sensory capabilities will be needed to further evaluate the posited taste component to human oral fat detection. Progress in this area should facilitate the translation of findings on how NEFA taste may contribute to or reflect food choice and chronic disease risk.

Associations Between BMI and Fat Taste Sensitivity in Humans

The objective of this study was to examine the reliability of associations between fat taste, hunger, dietary fat intake, and body mass index (BMI). Detection thresholds for oleic acid (OA) were obtained during each of 7 consecutive visits using a modified staircase procedure. Participants were 48 (N = 17 male; N = 31 female) healthy adults (mean age: 28.5 ± 10.4 years) with BMIs ranging from 18.9 to 47.2 (≥ 25 kg · m(-2), N = 24). OA detection thresholds and self-reported hunger (100-mm visual analog scale) were assessed at each visit. BMI and dietary fat intake (Block Rapid Fat Screener) were determined at baseline. There was a significant decrease of threshold concentration over repeated trials among lean and overweight (BMI between 25.0 and 29.9 kg · m(-2)) participants but not in the obese. Combining the lean and overweight and contrasting their responses to the obese revealed the lean plus overweight group to be significantly more sensitive at visits 6 and 7. No change of threshold sensitivity or correlation with fat intake was observed in the obese participants unlike findings in the lean and lean plus overweight participants. Correlations between saturated fat intake and threshold sensitivity were positive (greater intake associated with higher thresholds) at baseline for the group, with additional correlations observed among the lean plus overweight but not in the obese, leaving open questions about the nutritional significance of the association. No significant associations were observed between sensitivity to OA and hunger. Repeated testing is required to assess associations between fat taste and other outcome variables.

Influences of Repeated Testing on Nonesterified Fatty Acid Taste

Findings that support the ability of humans to taste nonesterified fatty acids have been qualified by claims of substantial individual variability in sensitivity. We tested whether the number of testing visits impacted detection thresholds. Additionally, we explored the possibility that methodological differences in reported studies contributed to the high level of variance. Participants were randomized to either the modified staircase or ascending 3-alternative forced-choice methods, completed 10 test visits, and then switched to the alternate method. Repeated testing lowered the threshold concentration, and regardless of starting method, threshold concentrations were significantly lower with the second method. The staircase method generated data with less variation. The ascending method appears to be able to distinguish hypo and hypersensitive individuals as the variance at each visit increased over time, suggesting that the top performers continued to improve while the hyposensitive subjects maintained their low level of performance. The best individual threshold performance (lowest stimulus concentration) at each visit was obtained with the ascending method for 7 out of the first 10 visits (P = 0.117) and 17 out of the 20 visits (P = 0.001). Despite potential advantages of the ascending method in terms of sensitivity separation, there was no difference between the median of the first 10 visits, second 10 visits, and overall median obtained by the 2 testing methods. The most appropriate detection threshold testing method will depend on the goals of the researcher.

Mechanisms and effects of “fat taste” in humans

Evidence supporting a “taste” cue from fat in the oral cavity continues to accrue. The proposed stimuli for fat taste, non‐esterified fatty acids (NEFA), are released from food through hydrolytic rancidity and lipase activity derived from foods or saliva. NEFA must then be released from the food matrix, negotiate the aqueous environment to reach taste cell surfaces, and interact with receptors such as CD36 and GPR120 or diffuse across cell membranes to initiate a taste signal. Knowledge of these processes in non‐gustatory tissues should inform understanding of taste responses to NEFA. Additionally, downstream effects of oral triglyceride exposure have been observed in numerous studies. Data specific to effects of NEFA versus triglyceride are scarce, but modified sham feeding trials with triglyceride document cephalic phase responses including elevations in serum lipids and insulin as well as potential, but debated, effects on gut peptides, appetite, and thermogenesis. In this review, we highlight the mechanisms by which NEFA migrate to and interact with taste cells, and then we examine physiological responses to oral fat exposure.

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.

Do non-nutritive sweeteners influence acute glucose homeostasis in humans? A systematic review

The human body associates sensory cues with metabolic consequences. Exposure to sweet-tasting sugars - even in the absence of ingestion - triggers physiological responses that are associated with carbohydrate digestion, absorption and metabolism. These responses include the release of insulin and incretin hormones, which work to reduce blood glucose. For this reason, non-nutritive sweeteners (NNS) have been posited to trigger similar physiological responses and reduce postprandial blood glucose concentrations. The first part of this review presents a brief overview of sweet taste receptor activation in the oral cavity and gastrointestinal tract and the ensuing physiological responses related to glucose homeostasis. The second part of this review contains a systematic literature review that tested the hypothesis that NNS use improves glucose regulation postprandially. Studies were grouped based on sweet taste receptor stimulation paradigms, including pre-ingestive stimulation, ingestion of NNS alone, co-ingestion of NNS with foods, and using NNS as preloads to influence subsequent blood glucose excursions. In summary, the review found that NNS triggered physiological responses, albeit inconsistently, yet failed to significantly lower blood glucose levels in almost all studies.

Changes in taste preference and steps taken after sleep curtailment.

A substantial proportion of the population does not achieve the recommended amount of sleep. Previous work demonstrates that sleep alterations perturb energy balance by disrupting appetite hormones, increasing energy intake, and decreasing physical activity. This study explored the influence of sleep duration on taste perception as well as effects on dietary intake and physical activity. Participants (n=24 habitual short sleepers and n=27 habitual long sleepers, 82.4% female, 88.2% white, 25.2±7.7years) completed two randomized taste visits; one following short sleep duration (≤7h) and one following long sleep duration (>7h). Taste perception measures included sweet and salt detection thresholds (ascending 3-alternative, forced-choice method), as well as sweet preference (Monell 2-series, forced-choice, paired-comparison, tracking method). Steps and sleep were tracked via FitBit, an activity monitoring device. Dietary intake was assessed using 24-hour recalls and analyzed using Nutritionist Pro. Habitual long-sleepers had a higher sweet taste preference (p=0.042) and took fewer steps (p=0.036) following sleep curtailment compared to the night where they slept >7h but did not experience changes in dietary intake or detection thresholds. Habitual short-sleepers did not experience changes in taste perception, activity, or dietary intake following sleep alteration. Habitual long-sleepers may be at greater risk of gaining weight when typical sleep patterns are disrupted.

Satiation, satiety: the puzzle of solids and liquids

Abstract: Identifying factors contributing to weight gain is critical if the obesity problem is to be adequately addressed. Nutritively sweetened beverage consumption trends closely parallel recent obesity prevalence data. This chapter reviews evidence for and against beverages as drivers of weight gain and also proposes possible mechanisms of action by which beverages could lead to decreased satiety and increased intake. Specifically, evidence exists for differences between solids and beverages in terms of cognitive effects, oral processing, gastric emptying time, gastrointestinal tract transit time, and endocrine responses. Collectively, these data indicate that energy delivered in beverages elicits weaker physiological responses associated with satiety and dietary compensation, and that the energy from beverages may pose a greater risk to weight management than solid food forms.

Chemosensory Properties of Pungent Spices: Their Role in Altering Nutrient Intake

BackgroundThe general population is not compliant with national dietary recommendations for promoting health and reducing chronic disease risk. While rising obesity rates suggest that the majority of the population is overconsuming, many individuals affected with either acute or chronic diseases struggle to maintain adequate dietary intake and are at high nutritional risk. Flavor is the primary driver of food intake; however, disliked flavors are a major barrier to consumer adherence with dietary recommendations for both groups. Spices that contribute to chemical burn—such as black pepper, garlic, ginger, mustard, oregano, red pepper, and wasabi—alter food flavors.PurposeThis paper explores the role of these pungent spices in altering nutrient intake across the lifespan. The role of chemical burn in manipulating dietary intake in both diseased and healthy populations is discussed.ApplicationImplications for using pungent spices to enhance compliance with dietary manipulations are described. Proposed functions of pungent spices are maintaining, preserving, and enhancing flavor to offset the reductions in liking and palatability that are associated with dietary modifications and disease status.

Relationship Between Body Fat and Physical Fitness in Army ROTC Cadets

The Army Physical Fitness Test (APFT), including timed push-ups, sit-ups, and run, assesses physical performance for the Army. Percent body fat is estimated using height and circumference measurements. The objectives of the study were to (a) compare the accuracy of height and circumference measurements to other, more accepted, body fat assessment methods and (b) determine the relationships between body composition and APFT results. Participants included Reserve Officer Training Corps (ROTC) cadets (n = 11 males, 2 females, 21.6 ± 3.5 years) from a midwestern university). At one visit, percent body fat was assessed using height and circumference measurements, air-displacement plethysmography, and bioelectrical impedance analysis. APFT results were provided by the ROTC director. All assessment methods for percent body fat were strongly associated (r ≥ 0.7, p < 0.01), implying that height and circumference measurement is a practical tool to estimate percent body fat of ROTC cadets. Total APFT score was not associated with any body fat assessment method. Push-up number was negatively associated with percent body fat by all assessment methods (r ≥ -0.8, p = 0.001), although run time was positively associated (r ≥ 0.6, p < 0.05). This suggests that percent body fat may be an important variable in determining or improving cardiovascular and muscular endurance, but not APFT performance.