the desire to eat. Appetite is influenced by a number of hormones (hormone) and neurotransmitters (neurotransmitter), which have been classified as appetite stimulants or appetite suppressants. Many of these substances are involved in mediating metabolic processes. For example, the gastrointestinal substance known as ghrelin, which regulates fat storage and metabolism, stimulates appetite. Likewise, agouti-related protein and neuropeptide Y, substances produced in the brain, act as appetite stimulants. In animals and humans appetite suppressants include melanocyte-stimulating hormone, insulin, and leptin, a protein hormone secreted by adipose (adipose cell) cells that acts on the hypothalamus in the brain.

Appetite is often associated with the desire to eat particular foods based on their smell, flavour, appearance, and appeal; this is a primary factor separating appetite from the primary motive of hunger. In addition, a person may be totally filled with food from a meal and still have an “appetite” for dessert. Furthermore, appetite may be increased or diminished depending on pleasant or unpleasant experiences associated with certain foods.