Food intake, energy balance and body weight control.

Obesity is a multifactorial and complex affectation that is characterized by a long-term excess energy intake (EI) above energy expenditure (EE). Since fat oxidation seems to be dependent on SNS activation and also seems to remain acutely unaffected by fat intake, this macronutrient is certainly partly responsible for this situation. In addition, high-fat intake does not induce as potent satiety signals or a compensation effect on subsequent EI as do diets rich in carbohydrates or proteins. Moreover, since alcohol intake acutely inhibits fat oxidation and does not promote subsequent compensation for its energy content, it should consequently be regarded as a substrate which can induce a positive energy balance under free-living conditions. Thus, in a weight reducing context, each energy substrate should be manipulated while taking into account its specific characteristics. Obesity has also often been associated to a decreased sympathetic nervous system (SNS) activity, hence sympathomimetic agents have been proposed as a possible way to partially correct this situation. Two of these agents are the widely consumed caffeine (CAF) and the pungent principle of hot red pepper, capsaicin (CAP), which acutely increase EE and reduce EI under some circumstances. Furthermore, other factors like dietary fibers, that have been shown to increase satiety and fullness, and reduce EI in some cases, should also be considered.