The hormone that anticipates meals
Ghrelin is produced mainly by cells in the stomach lining and is the best characterized hunger-promoting hormone. Its most striking feature is that it rises before an expected meal rather than only when the stomach is empty. In people on regular schedules, ghrelin climbs in the run-up to habitual eating times, which is why it is described as an oscillator tied to routine.
After eating, ghrelin falls sharply, with the size of the drop influenced by what was eaten. Protein and fiber tend to blunt ghrelin more durably than rapidly absorbed carbohydrate.
Why eating habits shape the curve
Because the rises are partly learned and anticipatory, meal timing and routine can reshape the pattern over days, which is part of why appetite often adjusts to a new eating schedule. Ghrelin also interacts with longer-term signals such as leptin, so it is one input among several, not the sole driver of hunger.
This is general educational information, not medical advice; appetite, weight, or eating-pattern concerns should be discussed with a qualified professional.