The “hunger hormone” and how it drives appetite.
What the evidence says
- Produced primarily by stomach — “hunger hormone” signals brain to stimulate appetite[1]
- Rises nearly twofold before expected meal times (preprandial), falls to trough within 1 hour after eating[1]
- Has strong learned/conditioned component — adapts to eating schedule; when the eating window shifted to 8 AM–2 PM, mean ghrelin decreased by 32 pg/mL despite an 18-hour daily fast (p=0.006)[1],[2]
- Follows circadian rhythm: nadir at ~0900, zenith at ~0100; pattern reciprocal to insulin and exactly in phase with leptin over 24 hours[1]
- Ghrelin is the only known hormone that increases food intake — it works by increasing the number of meals initiated (not their size) and elicits appetitive feeding behaviours; it also increases gastrointestinal motility while decreasing insulin secretion[3]
- Circulating ghrelin levels respond compensatorily to weight change: rising with weight loss and falling with weight gain — this contributes to the difficulty of maintaining weight loss[3]
- Ghrelin shows ”a strong inverse temporal association” with cortisol (r = -0.79, P < 0.0001), which the authors call novel and leave open: ghrelin "appears to be related to cortisol. However, further studies are needed" (corrected 2026-09-19 from a mechanism — "when cortisol peaks in the morning, ghrelin is suppressed; when cortisol drops in the afternoon, ghrelin rises" — that the authors do not claim)[4]
- The review reports that ghrelin released during fasting enhances hippocampal plasticity, neurogenesis and learning while reducing anxiety — an animal-model finding relayed by a review, not a human result[5]