How palatable food disrupts appetite regulation.

Appetite regulation is part of a feedback system that controls the energy balance, involving a complex interplay of hunger and satiety signals, produced in the hypothalamus as well as in peripheral organs. Hunger signals may be generated in peripheral organs (e.g. ghrelin) but most of them are expressed in the hypothalamus (neuropeptide Y, orexins, agouti-related peptide, melanin concentrating hormone, endogenous opiates and dopamine) and are expressed during situations of energy deficiency. Some satiety signals, such as cholecystokinin, glucagon-like peptide 1, peptide YY and enterostatin are released from the digestive tract in response to food intake. Others, such as leptin and insulin, are mobilized in response to perturbations in the nutritional state. Still others are generated in neurones of the hypothalamus (alpha-melanocyte-stimulating hormone and serotonin). Satiety signals act by inhibiting the expression of hunger signals and/or by blunting their effect. Palatable food, i.e. food rich in fat and sugar, up-regulates the expression of hunger signals and satiety signals, at the same time blunting the response to satiety signals and activating the reward system. Hence, palatable food offsets normal appetite regulation, which may explain the increasing problem of obesity worldwide.