Taste and Smell Physiological Mechanisms and Their Health Implications

Taste and olfaction play a key role in individuals’ behaviors, their interactions with the environment and memory processes, furthermore, they represent the most important factors influencing food preferences and therefore eating behavior, diet, metabolism, and health. Physiological variations or disorders in these two sensory modalities can have significant effects on the life’s quality or constitute risk factors for the onset of metabolism disorders, worsening nutritional status, overweight and obesity, or pathogenesis of different diseases. The purpose of this work was to investigate the function of taste and olfaction and their mechanisms controlling individual variability, and therefore nutrition and health. Firstly, we evaluate the degree of the peripheral taste function activation in response to the six taste qualities by electrophysiological recordings from human tongue and characterized its variability in relation with PROP phenotype (the most known example of taste variability genetically determined) and fungiform papillae density. The results, by showing that each taste quality evoked a specific monophasic depolarization in the human tongue whose amplitude was associated with PROP phenotype and fungiform papillae density, provided important information about the cellular organization and function of the human peripheral taste system that can explain the individual variability across taste qualities. Specifically, the electrophysiological responses to oleic acid were associated with rs1761667 SNP in the CD36 gene allowing to better understand the mechanisms involved in the choice of fat-rich foods. Secondly, we evaluated the role of salivary proteins in the development of astringency and in affecting BMI, in the context of PROP taster status and gender. Results showed that variation in the salivary protein composition (increases of the acidic proline-rich proteins, aPRPs), related to PROP taster status and gender, could influence variation in astringency perception or drive possible unbalance food habits which could lead to obesity. Furthermore, we analyzed the perception for six taste qualities, olfactory performance, and specific taste/olfactory genes, in relation with BMI, in patients with inflammatory bowel disease (IBD) and studied taste and smell sensitivity in severe obese subject that underwent to a bariatric surgery. Results showed that taste and olfaction impairments, explained by the oral pathologies and microbiome variations known for IBD patients, and the high frequency of non-taster allele in CD36 polymorphism (r1761667), can justify their typical dietary behaviors, and thus they may be significant risk factors that contribute to the pathogenesis of IBD. Results also showed an overall improvement in taste and olfactory performance, an increase in cognitive restraint, and a decrease in disinhibition and hunger after bariatric surgery, which were associated with PROP phenotype. These findings indicate that bariatric surgery can have a positive impact on olfactory and gustatory functions and eating behavior (with an important role of genetic), which in turn might contribute to the success of the intervention. Finally, since deficits in olfaction and taste have also been associated to many health markers including neurodegenerative diseases and specifically are among the most frequent non-motor manifestations in Parkinson’s disease (PD), we focused on reviewed the most relevant molecular and genetic factors involved in these impairments and their associations with the microbiota, with the aim to highlight that the basis of these dysfunctions are likely multifactorial and may include the same determinants responsible for other non-motor. In conclusion, these results show that the function of taste and olfaction and their genetic and molecular mechanisms are involved in the individual physiological variability which, in turn, control different biological process.