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

Effects of genetics on odor perception: Can a quick smell test effectively screen everyone?

SCENTinel, a rapid smell test designed to screen for olfactory disorders, including anosmia (no ability to smell an odor) and parosmia (distorted sense of smell), measures 4 components of olfactory function: detection, intensity, identification, and pleasantness. Each test card contains one of 9 odorant mixtures. Some people born with genetic insensitivities to specific odorants (i.e. specific anosmia) may fail the test if they cannot smell an odorant but otherwise have a normal sense of smell. However, using odorant mixtures has largely been found to prevent this from happening. To better understand whether genetic differences affect SCENTinel test results, we asked genetically informative adult participants (twins or triplets, N = 630; singletons, N = 370) to complete the SCENTinel test. A subset of twins (n = 304) also provided a saliva sample for genotyping. We examined data for differences between the 9 possible SCENTinel odors; effects of age, sex, and race on SCENTinel performance, test-retest variability; and heritability using both structured equation modeling and SNP-based statistical methods. None of these strategies provided evidence for specific anosmia for any of the odors, but ratings of pleasantness were, in part, genetically determined (h2 = 0.40) and were nominally associated with alleles of odorant receptors (e.g. OR2T33 and OR1G1; P < 0.001). These results provide evidence that using odorant mixtures protected against effects of specific anosmia for ratings of intensity but that ratings of pleasantness showed effects of inheritance, possibly informed by olfactory receptor genotypes.

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.

Physiology of Taste Processing in the Tongue, Gut, and Brain

The gustatory system detects and informs us about the nature of various chemicals we put in our mouth. Some of these have nutritive value (sugars, amino acids, salts, and fats) and are appetitive and avidly ingested, whereas others (atropine, quinine, nicotine) are aversive and rapidly rejected. However, the gustatory system is mainly responsible for evoking the perception of a limited number of qualities that humans taste as sweet, umami, bitter, sour, salty, and perhaps fat [free fatty acids (FFA)] and starch (malto-oligosaccharides). The complex flavors and mouthfeel that we experience while eating food result from the integration of taste, odor, texture, pungency, and temperature. The latter three arise primarily from the somatosensory (trigeminal) system. The sensory organs used for detecting and transducing many chemicals are found in taste buds (TBs) located throughout the tongue, soft palate esophagus, and epiglottis. In parallel with the taste system, the trigeminal nerve innervates the peri-gemmal epithelium to transmit temperature, mechanical stimuli, and painful or cooling sensations such as those produced by changes in temperature as well as from chemicals like capsaicin and menthol, respectively. This article gives an overview of the current knowledge about these TB cells' anatomy and physiology and their trigeminal induced sensations. We then discuss how taste is represented across gustatory cortices using an intermingled and spatially distributed population code. Finally, we review postingestion processing (interoception) and central integration of the tongue-gut-brain interaction, ultimately determining our sensations as well as preferences toward the wholesomeness of nutritious foods. © 2021 American Physiological Society. Compr Physiol 11:1-35, 2021.

The genetics of eating behaviors: research in the age of COVID-19

How much pleasure we take in eating is more than just how much we enjoy the taste of food. Food involvement - the amount of time we spend on food beyond the immediate act of eating and tasting - is key to the human food experience. We took a biological approach to test whether food-related behaviors, together capturing food involvement, have genetic components and are partly due to inherited variation. We collected data via an internet survey from a genetically informative sample of 419 adult twins (114 monozygotic twin pairs, 31 dizygotic twin pairs, and 129 singletons). Because we conducted this research during the pandemic, we also ascertained how many participants had experienced COVID-19-associated loss of taste and smell. Since these respondents had previously participated in research in person, we measured their level of engagement to evaluate the quality of their online responses. Additive genetics explained 16-44% of the variation in some measures of food involvement, most prominently various aspects of cooking, suggesting some features of the human food experience may be inborn. Other features reflected shared (early) environment, captured by respondents' twin status. About 6% of participants had a history of COVID-19 infection, many with transitory taste and smell loss, but all but one had recovered before the survey. Overall, these results suggest that people may have inborn as well as learned variations in their involvement with food. We also learned to adapt to research during a pandemic by considering COVID-19 status and measuring engagement in online studies of human eating behavior.

The genetics of eating behaviors: research in the age of COVID-19

How much pleasure we take in eating is more than just how much we enjoy the taste of food. Food involvement - the amount of time we spend on food beyond the immediate act of eating and tasting - is key to the human food experience. We took a biological approach to test whether food-related behaviors, together capturing food involvement, have genetic components and are partly due to inherited variation. We collected data via an internet survey from a genetically informative sample of 419 adult twins (114 monozygotic twin pairs, 31 dizygotic twin pairs, and 129 singletons). Because we conducted this research during the pandemic, we also ascertained how many participants had experienced COVID-19-associated loss of taste and smell. Since these respondents had previously participated in research in person, we measured their level of engagement to evaluate the quality of their online responses. Additive genetics explained 16-44% of the variation in some measures of food involvement, most prominently various aspects of cooking, suggesting some features of the human food experience may be inborn. Other features reflected shared (early) environment, captured by respondents' twin status. About 6% of participants had a history of COVID-19 infection, many with transitory taste and smell loss, but all but one had recovered before the survey. Overall, these results suggest that people may have inborn as well as learned variations in their involvement with food. We also learned to adapt to research during a pandemic by considering COVID-19 status and measuring engagement in online studies of human eating behavior.

GPR120 agonists enhance the fatty orosensation when added to fat-containing system, but do not evoke it by themselves in humans

Dietary fat, an important macronutrient, has been considered to be perceived by texture and olfaction. Recently, fatty acid transporter, CD36, and fatty acid receptor, GPR120 are considered to be involved in human gustatory fatty acids perception in humans. However, limited information is currently available to show that agonists of CD36 and GPR120 evoke fatty oral sensations regarding to dietary fat in humans. Therefore, the role of GPR120 agonists in dietary fat perception in humans was investigated herein. An emulsion prepared from vegetable oil had a stronger fatty orosensation, an orosensation similar to an oily mouth-coating sensed 5 - 10 s after tasting, than that prepared from mineral oil; however, the physical properties of both emulsions, such as viscosity, particle distribution, interfacial tension, contact angle, frictional load, and ζ-electric potential were similar. The potent GPR120 agonist, TUG-891 enhanced the fatty orosensation when added to the emulsion prepared from vegetable oil, but not to that from mineral oil. All GPR120 agonists tested enhanced the fatty orosensation when added to a low-fat food system whereas they did not evoke any fatty sensation in aqueous solution at the concentrations tested in food system, and sensory activity positively correlated with GPR120 activity. These results suggest that GPR120 agonists enhance the fatty orosensation in humans when added to vegetable oil or a low-fat food system, but do not evoke it by themselves.