Your gut hormones decide when a meal ends
Hunger is not only an empty stomach. Ghrelin signals the brain to seek food; cholecystokinin, peptide YY, insulin, and fat-derived leptin push satiety. Eat too fast and those stops arrive late—one reason rapid eating tracks with overeating and weight gain.
Eating is ingestion for digestion: heterotrophs must take in organic matter because they cannot photosynthesize. Animals evolved diets from carnivory to herbivory to omnivory; fungi digest outside their bodies and so do not "eat" in the animal sense. Humans organize intake into meals and snacks, formal dining and banquets, guided by cooks and culinary craft. UK doctors often advise three daily meals of roughly 400–600 kcal each, spaced four to six hours, totaling about 1800–2000 kcal for an average person. Homes reserve kitchens and dining rooms; restaurants and festivals turn eating into public theater.
Infants start on milk alone; many meet purées between two and eight months, finger foods by eight to twelve months as teeth erupt, and adult textures near eighteen months, with neat etiquette often arriving only around five or six. Posture is cultural: floor sitting is common across much of the Middle East; Greeks, Romans, and Passover tradition favored reclining. Compulsive emotional eating rises with distress especially in obesity research; Lowe and Fisher found overweight students mainly overdid snacks eaten alone, not shared meals. Hormones including leptin, cholecystokinin, bombesin, and others can suppress intake.
Environmental cues—smell, sight, talk of food—join metabolic alarms when cellular glucose or lipids fall; the brain watches its own glucose while the liver monitors both fuels. Short-term fullness comes from taste, stomach stretch, intestinal peptides, and insulin; long-term stores speak through leptin from adipose tissue, which damps hypothalamic hunger peptides such as MCH and orexin. The brainstem carries hunger circuits, shown when decerebrate rats can only take liquid food. Stopping intake within two hours of sleep is linked to lower body weight. Psychology, illness, and deprivation can override the whole system—from anorexia to famine.
Source: Eating
