The Molecular Basis of Body Weight Control

摘要

Obesity is defined as a condition of excess body weight due to an increased amount of energy accumulated in the form of fat in adipose tissue depots. It can occur as a result of genetic or acquired changes in different types of biochemical processes leading, to an amount of energy intake that, in the long term, exceeds energy expenditure. Obesity and even a moderate overweight are viewed as pathological conditions when the excess and/or the type of excess fat are able to produce adverse health consequences. The rising incidence of obesity in developed Western countries is not conceivable as a consequence of a sudden genomic change but as a consequence of environmental changes. We do not know what are the precise environmental factors involved except that they are associated with the availability and composition of food in our rich societies and with the trend to less physical activity due to new life style habits and social requirements. Our organisms appear to be better adapted to avoid weight loss than to combat weight gain, probably because for many years our species has evolved under conditions of limited food supply. However, it is of note that the response to diet and the predisposi- tion to overweight gain varies widely between individuals, reflecting genetic and biochemical individuality of the body weight control mechanisms. Obesity represents the archetype of phenotypic complexity: very diverse processes or factors that affect the size and composition of any tissue, organ or individual system in our organism can affect body weight. However, only those factors that affect overall energy balance in the long term, and, consequently the amount of fat reserves, can be considered as part of the body weight control system. The present article is aimed to a conceptual description of these processes, their mechanisms and their interrelationships. Taken together, these processes define a coherent physiological system for the regulation of body fat reserves and body weight. In Figure 1 this system is schematically represented, highlighting the role of leptin in this complex regulatory net.