Ghrelin is a peptide hormone that regulates energy homeostasis by stimulating appetite and food intake. It is secreted by the stomach and its levels rise before meals and in response to fasting. Ghrelin activates neurons in the hypothalamus that stimulate appetite and feeding behavior. It also acts on reward centers in the brain to influence food motivation. Long-term, ghrelin promotes weight gain by increasing food intake and fat storage while reducing energy expenditure. Polymorphisms in the ghrelin and ghrelin receptor genes have been linked to obesity and eating disorders. Ghrelin antagonists may help treat obesity by reducing appetite and food intake.