Nowadays obesity resulting from abnormal or excessive fat deposits in a body has become a true epidemic. Risk factors that cause the disease include improper lifestyle, hereditary predisposition, as well as metabolic activity of gut microbiota. Research works performed over the last decades indicate that microbes that create colonies in human intestines play a significant role in maintaining proper metabolism. There is a correlation between disorders in gut microbiota structure and immune disorders, elevated susceptibility to infections, and obesity. There is more and more evidence that gut microbiota and its overall bacterial genome exert their influence on nutrients assimilation and regulate energy metabolism and fat accumulation. Certain differences were detected in microbiota gut structure in children and adults with obesity and people with proper body mass index. Delivery and feeding are among key factors influencing gut microbiota formation in a child. Thus, research results indicate that natural birth, as opposed to cesarean section, can prevent obesity occurrence in a child. Breast-feeding also makes a substantial contribution into development of an infant since breast milk is balanced food that provides optimal metabolism in an infant’s body and helps creating proper gut microbiota. At the same time, according to data obtained via numerous research works, artificial feeding can be related to obesity occurrence in future. Ways to fight obesity include medication therapy, dietary nutrition, physical activity as well as bariatric surgery; the latter is nowadays considered to be the most efficient procedure on the matter. Reduction in body mass via influencing gut microbiota is a promising trend in research in the sphere. Despite there are objective data on benign effects produced by probiotics and prebiotics on gut microbiota, experts haven’t been able to reach agreement on their efficiency yet.