The review article examines the issues of obesity regarding its prevalence, phenotypes, course and consequences. The anatomical, physiological and functional features of adipose tissue are discussed. The “Discussion” section presents the authors’ own clinical observations on therapeutic and surgical issues in the treatment of obesity. Currently, adipose tissue is divided into white, brown and beige. White and brown adipose tissue can turn into each other through the beige adipose tissue stage. The volume and activity of brown adipose tissue require greater expenditure in the metabolism of oxygen molecules and are more pronounced in women. The components of the extracellular matrix of adipose tissue are collagen types I, III, V, VI. The collagen structure of adipose tissue varies depending on the location, volume and size of fat, age, gender, functional state of the kidneys, thyroid gland, nature of food, energy expenditure and sleep patterns. With intense work and cold exposure, the hormone irisin is formed in skeletal muscles, which promotes the transformation of white adipose tissue into brown or beige, helps reduce body weight in obesity, and has a beneficial effect on the course of type 2 diabetes mellitus and associated diseases. Traditionally, obese individuals are divided into metabolically healthy obesity and metabolically unhealthy obesity based on the degree of metabolic disorders. In visceral fat, lipolysis occurs with high intensity, which supports the development of inflammation. In obesity, decreased expression of adiponectin accelerates the development of atherosclerotic cardiovascular diseases. As body weight increases, visceral adipose tissue acquires an inflammatory phenotype, manifested by increased expression of cytokines (interleukin-6, interleukin-1, interleukin-17, tumor necrosis factor-alpha), hyperactivation of the tissue renin-angiotensin-aldosterone system, as well as excessive cell infiltration immune system (leukocytes, neutrophils, T-lymphocytes, monocytes, macrophages). During inflammation in adipose tissue, inflammatory (M1) and atherogenic (M4) phenotypes of macrophages dominate. In morbid obesity, the number of macrophages in adipose tissue can reach up to 50% of all cells.
