[Leptin, ghrelin, and physical exercise]

Obesity is a major public health problem in the Western world resulting in serious social, physical and psychological damages. The genesis of obesity is complex involving a variety of factors such as genetic, psychological, metabolic and environmental factors. Progress in endocrinology and metabolism show that adipocyte is considered now as an endocrine tissue producing several substance including adiponectin, tumor necrosis factor-alpha, interleukin-6 and leptin. Specifically, leptin is the main peptide produced by the adipocyte and its serum concentration represents an important peripheral signal in the regulation of food intake and energy expenditure in mammals. In addition to leptin, a new peptide was discovered recently named ghrelin. Ghrelin, a peptide hormone identified in the stomach, is directly involved with the regulation of energy balance and obesity. Physical exercise has been used as a non-pharmacological tool in management of body weight and the effect of physical activity on weight control is an important issue for clinical studies in endocrinology field. Thus, this review will attempt to update the knowledge of leptin and ghrelin on the body weight regulation and the effect of exercise training on these peptide concentrations. It can be concluded that the relationship between physical exercise and the plasma concentration of these peptides is not clear. The reasons for that could be related to the differences in duration, intensity and frequency of the training program employed in each study. Indeed, most of the studies have not analyzed the intensity of training program by either plasma lactate concentration or maximum oxygen consumption. On the other hand, genetic basis could also explain the discrepancies found in some studies, since it has been shown that polymorphism for a variety of genes might be an important factor to determine the differences of cellular response to physical training.