Brain responses to high-protein diets.

Proteins are suspected to have a greater satiating effect than the other 2 macronutrients. After protein consumption, peptide hormones released from the gastrointestinal tract (mainly anorexigenic gut peptides such as cholecystokinin, glucagon peptide 1, and peptide YY) communicate information about the energy status to the brain. These hormones and vagal afferents control food intake by acting on brain regions involved in energy homeostasis such as the brainstem and the hypothalamus. In fact, a high-protein diet leads to greater activation than a normal-protein diet in the nucleus tractus solitarius and in the arcuate nucleus. More specifically, neural mechanisms triggered particularly by leucine consumption involve 2 cellular energy sensors: the mammalian target of rapamycin and AMP-activated protein kinase. In addition, reward and motivation aspects of eating behavior, controlled mainly by neurons present in limbic regions, play an important role in the reduced hedonic response of a high-protein diet. This review examines how metabolic signals emanating from the gastrointestinal tract after protein ingestion target the brain to control feeding, energy expenditure, and hormones. Understanding the functional roles of brain areas involved in the satiating effect of proteins and their interactions will demonstrate how homeostasis and reward are integrated with the signals from peripheral organs after protein consumption.