Smell and taste

This chapter provides an up-to-date overview of the nature and causes of chemosensory disturbances in older age, tools for their evaluation, and approaches useful for counselling patients and treating the underlying dysfunction. In addition to the sensory innervation of the olfactory nerve, free nerve endings of the trigeminal nerve are distributed throughout the nasal mucosa. Threshold tests establish the lowest concentration of an odorant that can be perceived or recognised as a quality. Odour identification tests determine the degree of a person's olfactory function. The loss of smell can be quite severe in patients with nasal sinus disease, with most being anosmic or profoundly hyposmic. Severe acute respiratory syndrome coronavirus 2, which causes coronavirus disease 2019, affects chemosensory functions. During the last decade, more extensive research in the area of central nervous diseases has accumulated evidence on neurodegenerative processes and impaired olfaction. Taste function, like olfactory function, declines over the lifespan. © 2022 John Wiley & Sons Ltd. All rights reserved.

Do Gut Microbes Taste?

Gut microbiota has emerged as a major metabolically active organ with critical functions in both health and disease. The trillions of microorganisms hosted by the gastrointestinal tract are involved in numerous physiological and metabolic processes including modulation of appetite and regulation of energy in the host spanning from periphery to the brain. Indeed, bacteria and their metabolic byproducts are working in concert with the host chemosensory signaling pathways to affect both short- and long-term ingestive behavior. Sensing of nutrients and taste by specialized G protein-coupled receptor cells is important in transmitting food-related signals, optimizing nutrition as well as in prevention and treatment of several diseases, notably obesity, diabetes and associated metabolic disorders. Further, bacteria metabolites interact with specialized receptors cells expressed by gut epithelium leading to taste and appetite response changes to nutrients. This review describes recent advances on the role of gut bacteria in taste perception and functions. It further discusses how intestinal dysbiosis characteristic of several pathological conditions may alter and modulate taste preference and food consumption via changes in taste receptor expression.