Olfactory Dysfunction in Obesity and Type 2 Diabetes

The article analyzes literature data on the close relationship between energy balance and sense of smell. Olfaction is one of the main modalities of hedonic evaluation of food. Odor is one of the most important sensory signals predicting food quality and plays a key role in food selection and consumption. Appetite can be stimulated by various stimuli, but the leading role belongs to olfactory signals (tasty smells) and levels of hormones that signal hunger and satiety. Olfactory perception is subject to hormonal modulation. In this regard, special attention in the article is paid to the modulating function of insulin. Insulin, one of the main metabolic hormones that controls food intake, has an anorexigenic effect not only at the level of the hypothalamus, but also at the level of the olfactory pathway, especially strong in the olfactory bulb. It has a rate of insulin transport two to eight times higher than in other parts of the brain, and it contains the highest concentration of insulin and the highest density of insulin receptor kinase. Thus, insulin is not only able to penetrate to the site of olfactory information processing, but do so quickly. At the same time, insulin and its receptors are localized in the olfactory epithelium, namely in mature olfactory sensory neurons. Therefore, insulin affects the primary stage of perception of an odorous molecule – odor detection, which occurs at the level of the olfactory epithelium. The sense of smell is impaired up to its complete loss in obesity and type 2 diabetes, worsening the quality of life of such patients. The paper examines the effectiveness of intranasal insulin administration to restore olfactory function in metabolic disorders and other diseases.