Ghrelin
The hunger hormone. Ghrelin rises before meals, triggering that "I need to eat" feeling. Made mostly in the stomach, it's the counterpart to leptin. But ghrelin does more than just make you hungry—it affects growth hormone, mood, reward pathways, and even memory.
What Ghrelin Does
Stimulates Appetite
Signals hypothalamus that stomach is empty. Creates hunger sensation. Rises before meals.
Releases Growth Hormone
Potent GH secretagogue. "Ghrelin" from "ghre" meaning growth. Promotes protein synthesis.
Activates Reward
Acts on dopamine pathways. Makes food more rewarding when hungry. Food tastes better.
Gastric Motility
Promotes stomach emptying. Prepares GI tract for food. Part of digestive preparation.
Memory
Enhances hippocampal function. Being slightly hungry may improve learning. Evolutionary advantage.
Mood
Has anti-anxiety and antidepressant effects. "Hangry" is real—low food = mood issues.
Ghrelin Patterns
Daily Rhythm
- Rises before habitual meal times
- Falls after eating (food suppresses it)
- Adapts to YOUR eating schedule
- Peaks correspond to when you normally eat
- Can be "retrained" by changing meal times
What Affects Levels
- Sleep deprivation: Increases ghrelin significantly
- Stress: Can raise or lower depending on type
- Protein: Suppresses ghrelin more than carbs
- Fasting: Initially rises, then adapts
- Weight loss: Rises (body fights fat loss)
Ghrelin and Fasting
Initial Rise
Ghrelin spikes at normal meal times when fasting. This is when hunger peaks.
Adaptation
After 16-24 hours, ghrelin often decreases. Body adapts. Hunger becomes more manageable.
Retraining
With intermittent fasting, ghrelin retrains to new schedule. Takes 1-2 weeks.
GH Benefits
Fasting-induced ghrelin raises growth hormone. Protective against muscle loss.