Short answers, pulled from the story.
Eating is the ingestion of solid food for digestion. In biology it provides heterotrophic organisms with the essential nutrients and energy needed for metabolism and physical growth, because they cannot acquire nutrition intrinsically like autotrophs.
Carnivores and scavengers eat flesh from other animals, while herbivores and algivores eat plants and algae. Omnivores consume both plant and animal matter, and detritivores and coprophages eat detritus and feces.
Most infants do not eat anything solid until they are between six and eight months old. Newborns cannot chew and survive solely on liquid breast milk or infant formula, though puréed baby food is sometimes given as early as two or three months.
Doctors in the UK recommend three meals a day, each between 400 and 600 kcal, spaced four to six hours apart. Three well-balanced meals amount to roughly 1800 to 2000 kcal, the average requirement for a regular person.
Ghrelin is released by the stomach to increase appetite and signal hunger to the brain. Satiety signals include cholecystokinin, Peptide YY 3-36, insulin, and leptin, the last of which is secreted by adipose tissue to suppress appetite.
Anorexia nervosa involves restricting calorie intake out of fear of gaining weight, leading to malnutrition and unhealthy weight. Bulimia involves recurrent binge eating followed by maladaptive behaviors such as induced vomiting, excessive physical activity, and laxatives.