Faim et satiété, contrôle de la prise alimentaire

Food intake is a complex periodical behaviour through which a living organism can extract vital nutrient and energy substances from the environment. Hunger and satiety are psycho-physiological states that, respectively, elicit or inhibit food intake. Homeostatic (glucostatic or lipostatic) and non-homeostatic (environmental conditions) mechanisms contribute to the periodic initiation of food intake. Once a meal has started, the stimulation to eat is progressively antagonized by the cumulative effects of the ingested foods. This satiation process brings the eating episode to an end before the ingested nutrients have been absorbed. Meal size is determined by an interaction of sensory (food quality and variety), gastro-intestinal, and neuroendocrine responses. A Pavlovian learning mechanism allows the metabolic consequences of ingesting a particular food to become associated with the sensory characteristics of the food; as a consequence, a unique repertoire of food acceptance and rejection responses is shaped for each individual eater. Satiety, the post-meal phase of inhibition of eating, depends on the nutrient composition of the meal and, mainly, on its energy density. The selection of high energy-density foods induces little satiety and favours “passive over-consumption”. In humans, culture, socio-economical status, family context, and even the physical characteristics of the environment affect food choices and energy intake. The mechanisms selected by Evolution in order to allow survival under environmental conditions of food shortage seem more efficient at correcting for energy needs than excesses. In the present context of food plethora, the obesity epidemic reflects both a biological bias and the potent stimulation from the environment.