The roles of genetic variation, adiposity, and diet in sensory perception and food preferences.

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Background: Human ingestive behaviour is a complex process influenced by many factors at molecular levels. Several common genetic variants have been implicated in taste sensitivity with subsequent links to food preferences and food intake. Overweight/obese individuals demonstrate higher detection thresholds for fatty acids, indicating reduced sensitivity to fatty acids in the oral cavity. Indeed, inflammation induced by excess adiposity may compromise taste and lead to overconsumption of energy-dense foods. However, manipulation of dietary intake has been demonstrated to alter taste thresholds and even acute stimulation of the oral cavity (oro-sensory stimulation) impacts physiological outcomes including appetite. Moreover, taste genes are expressed in olfactory tissues, but no previous work has evaluated olfactory abilities across taste gene variants. Thus, opportunities exist to more comprehensively evaluate taste perception, oro-sensory stimulation, and olfaction by considering exposure, adiposity, and genomic factors. Approach: This research program will evaluate relationships between genetics, adiposity status, and taste and olfactory perception by recruiting previous research participants who have genome-wide genotyping data available. The specific aims are to: 1) Conduct a recall-by-genotype controlled sensory evaluation experiment to characterize taste sensitivities and hedonic liking between obese and lean individuals with similar taste genetic backgrounds. 2) Determine the effect of short-term dietary fat restriction on fat taste detection and expression of taste genes in the oral cavity. 3) Determine the effect of pre-meal chemosensory mouth rinses (oro-sensory stimulation) on appetite, food intake, and gene expression according to adiposity status and genetic profiles. 4)Examine olfactory perception of aromas from sweet and fat odor samples between obese and lean participants with the same genetic background for fat and sweet taste perception. Existing genetic and body composition data will be examined to identify potential eligible participants for recontact according to prespecified criteria. Those who meet the inclusion criteria will be invited to participate in a series of studies to evaluate sensory perception outcomes according to sex, genetic background and adiposity status. The study sessions will characterize 1) baseline taste detection thresholds, 2) taste detection thresholds after a short-term period of dietary fat restriction,  3) appetite and ingestive behaviour outcomes following pre-meal oro-sensory stimulation with chemosensory mouth rinses using a crossover design, and 4) olfactory outcomes matching for taste genes and adiposity status. Significance: This research will clarify the roles of genetics, adiposity, and exposure in taste, olfaction, and food preferences, which will be relevant for understanding the multiple factors implicated in chemosensory detection and food preferences.