Obesity, metabolic syndrome and olfactory perception

Nowadays, it is well accepted that obesity and metabolic syndrome are diseases that constitute a global public health issue. In consequence, the interest in the study of the effects these pathologies produce in the central nervous system has greatly increased in the last decades. One of the most overlooked topics in the literature is the impact they exert in sensory systems, among which is olfaction. The olfactory system is related to a number of vital functions, like the activation of defense mechanisms, contribution to appetitive and digestive reflexes, recognition of conspecifics, and even has socio-sexual implications. It has been discovered that the olfactory system also plays a crucial role in food intake, the choice of foods, appetite and satiety mechanisms; therefore, it is involved in obesity development. Clinical studies have proven that obese patients exhibit hyposmia more frequently than aged-matched healthy controls. Olfactory alterations have also been found in obese rodents or in animals with similar features of human metabolic syndrome. The causes of this association are still being investigated. This work reviews the studies that have tried to understand this association from a preclinical and clinical approach as well as those biological mechanisms that could be involved. The evidences here presented suggest that obesity and metabolic syndrome affect the adequate function of olfactory sensory system.