Regulation of body weight in humans

The mechanisms involved in body weight regulation in humans include genetic , physiological, and behavioral factors. Stability of body weight and body composition requires that energy intake matches energy expenditure and that nutrient balance is achieved. Human obesity is usually associated with hig h rates of energy expenditure. In adult individuals, protein and carbohydra te stores vary relatively little, whereas adipose tissue mass may change ma rkedly. A feedback regulatory loop with three distinct steps has been recen tly identified in rodents: 1) a sensor that monitors the size of adipose ti ssue mass is represented by the amount of leptin synthesized by adipose cel ls (a protein encoded by the ob gene) which determines the plasma leptin le vels; 2) hypothalamic centers, with specific leptin receptors, which receiv e and integrate the intensity of the signal; and 3) effecter systems that i nfluence the two determinants of energy balance, i.e., energy intake and en ergy expenditure. With the exception of a few very rare cases, the majority of obese human subjects have high plasma leptin levels that are related to the size of their adipose tissue mass. However, the expected regulatory re sponses (reduction in food intake and increase in Energy expenditure) are n ot observed in obese individuals. Thus obese humans are resistant to the ef fect of endogenous leptin, despite unaltered hypothalamic leptin receptors. Whether defects in the leptin signaling cascade play a role in the develop ment of human obesity is a field of great actual interest that; needs furth er research. Present evidences suggest that genetic and environmental facto rs influence eating behavior of people prone to obesity and that diets that are high in fat or energy dense undermine body weight regulation by promot ing an overconsumption of energy relative to need.