Ghrelin

Ghrelin is a 28-amino-acid peptide hormone secreted primarily by enteroendocrine cells of the stomach, with smaller contributions from the pancreas and small intestine. It is the principal "hunger hormone" in humans — ghrelin levels rise before meals, stimulate appetite in the hypothalamus, and fall after food intake.

Physiological role

• Appetite stimulation via AgRP/NPY neurons in the arcuate nucleus of the hypothalamus.
• Gastric emptying — promotes forward movement of stomach contents.
• Growth-hormone release — ghrelin was originally identified as a growth-hormone secretagogue, which is how it got its name (from Proto-Indo-European "ghre" meaning "grow").
• Reward-system engagement — acts on dopaminergic neurons in the ventral tegmental area, contributing to the rewarding quality of food.

Ghrelin and meal timing

Ghrelin shows a distinctive pre-meal rise followed by post-meal suppression. Crucially, this pattern is learned. If you habitually eat breakfast at 8 a.m., ghrelin rises around 7:30 a.m.; if you habitually skip breakfast, the rise shifts to your first real meal of the day. This is the physiological basis of why "intermittent fasting" gets easier with time — the hunger pattern remaps to the new eating window.

Ghrelin and weight loss

One of the most durable findings in obesity research: after sustained weight loss, fasting ghrelin levels rise and post-meal ghrelin suppression weakens. Sumithran et al. (2011) followed subjects one year after a structured 10% weight-loss intervention and found ghrelin remained elevated well above baseline a full year later — alongside persistently elevated hunger ratings.

This is not a failure of willpower. It is a physiological signal that the body is actively working to restore previous weight. Any long-term maintenance-after-weight-loss strategy has to account for this persistent hunger pressure.

Ghrelin and sleep

Sleep deprivation elevates ghrelin and suppresses leptin — a dual shift that drives up appetite. Even a single night of short sleep (< 5 hours) is enough to produce measurable next-day changes in hunger ratings and food intake. This is probably the single most underappreciated contributor to unexplained appetite rise during a diet.

Bariatric surgery and ghrelin

Gastric bypass and sleeve gastrectomy both reduce circulating ghrelin levels in the months following surgery — one hypothesised mechanism for the appetite suppression that accompanies these procedures beyond what volume restriction alone would predict.

Can you lower ghrelin with diet?

Food choices affect ghrelin suppression after meals, but the magnitude is modest. High-protein meals suppress ghrelin more than high-carbohydrate or high-fat meals at the same calorie load. Fibre modestly extends the suppression window. Liquid calories suppress ghrelin weakly compared to the same calories in solid form. None of these is a pharmacological-scale effect, and the main clinical leverage on ghrelin is through surgical procedures or GLP-1-class drugs.