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Human appetite is a complex process controlled by both physical and psychological factors.

Physical causes:

Lower blood glucose levels: After food is digested, glucose is absorbed into the blood and used for energy in the body's cells. When blood glucose levels drop, the brain sends "hunger" signals.
Hormones: Two hormones called ghrelin and leptin play an important role in controlling appetite. Ghrelin increases appetite, while leptin decreases appetite.
Digestive System: On an empty stomach, receptors located on the stomach wall send signals to the brain that create feelings of hunger.
Psychological factors:

Habit: If you have a habit of eating at certain times, you are more likely to feel hungry at that time.
Emotions: Emotions such as stress, anxiety, boredom or loneliness can increase or decrease appetite.
Mental illness: Certain mental illnesses such as anorexia nervosa and bulimia nervosa can distort the sense of hunger.
Medicines: Some medicines increase or decrease appetite as a side effect