Leptin, ghrelin, and GLP-1
Appetite is not controlled by a single switch. Signals from the gut, fat tissue, pancreas, and nervous system reach brain circuits that coordinate hunger, satiety, meal timing, and energy balance. Leptin, ghrelin, and GLP-1 are useful landmarks in that network, provided each is kept in its proper context.
Leptin reflects stored energy
Leptin is produced mainly by adipose tissue, with additional production in places such as the stomach and intestine. Circulating leptin communicates information about energy stores to receptors in the central nervous system, including the hypothalamus. In the appetite system described in NCBI reviews, leptin is associated with satiety signalling and lower appetite drive.
The signal is not a simple readout that predicts every meal. Leptin levels and responses vary with energy state and other physiological factors, and the same review describes elevated leptin alongside reduced responsiveness in obesity. The biology is therefore a feedback system, not a willpower score.
Ghrelin rises around hunger
Ghrelin is produced in the gastrointestinal tract, especially by the stomach. The NCBI appetite review describes secretion by the empty stomach and suppression after eating, which is why ghrelin is often called a hunger signal. It also participates in other processes, including the sleep–wake cycle and glucose-related signalling.
A meal does not produce one identical hormonal pattern every time. Ghrelin suppression can vary with the food consumed and with circadian timing, so the signal is part of a changing biological rhythm rather than a fixed countdown to eating.
GLP-1 links the gut and brain
GLP-1 is released by intestinal L cells after nutrients reach the gut. NCBI describes effects through gut vagal pathways and hypothalamic nuclei that contribute to satiety. It also stimulates glucose-dependent insulin release and slows gastric emptying, showing why appetite physiology overlaps with digestion and glucose regulation.
Naturally secreted GLP-1 is short-lived because the enzyme DPP-4 rapidly breaks it down. Medicines that activate the same receptor are designed for different exposure; they are distinct from the hormone released after a meal.
References
Source-checked educational draft. Human editorial review pending.
NIH National Library of MedicinePhysiology, Appetite And Weight RegulationSource accessed 2026-09-05NIH National Library of MedicinePhysiology, LeptinSource accessed 2026-09-05NIH National Library of MedicineBiochemistry, GhrelinSource accessed 2026-09-05