Appetite Regulation: Physiologic mechanisms which regulate or control the appetite and food intake.Appetite: Natural recurring desire for food. Alterations may be induced by APPETITE DEPRESSANTS or APPETITE STIMULANTS.Peptide YY: A 36-amino acid peptide produced by the L cells of the distal small intestine and colon. Peptide YY inhibits gastric and pancreatic secretion.Ghrelin: A 28-amino acid, acylated, orexigenic peptide that is a ligand for GROWTH HORMONE SECRETAGOGUE RECEPTORS. Ghrelin is widely expressed but primarily in the stomach in the adults. Ghrelin acts centrally to stimulate growth hormone secretion and food intake, and peripherally to regulate energy homeostasis. Its large precursor protein, known as appetite-regulating hormone or motilin-related peptide, contains ghrelin and obestatin.Satiation: Full gratification of a need or desire followed by a state of relative insensitivity to that particular need or desire.Eating: The consumption of edible substances.Hypothalamus: Ventral part of the DIENCEPHALON extending from the region of the OPTIC CHIASM to the caudal border of the MAMMILLARY BODIES and forming the inferior and lateral walls of the THIRD VENTRICLE.Leptin: A 16-kDa peptide hormone secreted from WHITE ADIPOCYTES. Leptin serves as a feedback signal from fat cells to the CENTRAL NERVOUS SYSTEM in regulation of food intake, energy balance, and fat storage.Obesity: A status with BODY WEIGHT that is grossly above the acceptable or desirable weight, usually due to accumulation of excess FATS in the body. The standards may vary with age, sex, genetic or cultural background. In the BODY MASS INDEX, a BMI greater than 30.0 kg/m2 is considered obese, and a BMI greater than 40.0 kg/m2 is considered morbidly obese (MORBID OBESITY).Body Weight: The mass or quantity of heaviness of an individual. It is expressed by units of pounds or kilograms.Appetite Depressants: Agents that are used to suppress appetite.Appetite Stimulants: Agents that are used to stimulate appetite. These drugs are frequently used to treat anorexia associated with cancer and AIDS.Hunger: The desire for FOOD generated by a sensation arising from the lack of food in the STOMACH.Satiety Response: Behavioral response associated with the achieving of gratification.Anorexia: The lack or loss of APPETITE accompanied by an aversion to food and the inability to eat. It is the defining characteristic of the disorder ANOREXIA NERVOSA.