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The gastrointestinal system, particularly the stomach, releases a peptide hormone called ghrelin. In 1999 experiments have revealed that hunger is communicated from the stomach to the brain via this hormone peptide. This peptide can stimulate thought about food, and is suppressed after food is ingested. Nutrient injection into the blood stream does not suppress ghrelin, so the release of hormone is directed by the digestive system and not by nutrient availability in the blood. . These blood levels of ghrelin increase with fasting and are reduced after a meal. Ghrelin antibodies or ghrelin receptor antagonists inhibit eating. Ghrelin also stimulates energy production and signals directly to the hypothalamus regulatory nucli that control energy homeostasis.