With a growing number of the elderly population, it is important to remember about the potential pathologic conditions, one of the main features of which is the weight loss (cachexia, anorexia, sarcopenia, hypermetabolism/hypercatabolism syndrome and etc.). These processes are interrelated and interdependent, especially in old age, and even modern medical literature does not clearly indicate the boundaries between this syndromes and pathological conditions. For instance, cachexia is a complex metabolic syndrome, resulting in the loss of muscle, but not always fat mass, arises in connection with the development of severe chronic systemic inflammation, which is especially inherent in the elderly, often accompanied by anorexia, and may also be part of another "old age syndrome"--sarcopenia. Sarcopenia is an age-related atrophic degenerative change in skeletal muscle, which occurs as a result of a long process with a very complex mechanism and is characterized by progressive and generalized decrease in muscle mass, its strength and by a risk of developing complications such as disturbance of mobility. Meanwhile, the earlier a physician suspects the onset of cachexia syndrome and/or other conditions involving abnormal weight loss, the more effective are going to be attempts to correct them with possible agents, which help to improve the prognosis and prolong life of the patient.