Ghrelin — Hunger Is Made by Hormones, Not Your Stomach

"I automatically get hungry at lunchtime." That's not because your stomach is empty. A hormone sends scheduled signals to your brain.

What Is Ghrelin?

Ghrelin is a peptide hormone discovered in 1999 by a Japanese research team (Kojima Masayuki et al.). It's mainly secreted by the fundus of the stomach.

Name origin: GH (Growth Hormone) + rel(release) + in. But its key function turned out to be appetite stimulation.

How It Works

1. Secretion Timing

• Fasting: Blood ghrelin spikes (peaks 30min-1hr before meals)

• After eating: Drops sharply when food enters stomach

• During sleep: Gradually rises toward dawn (why you're hungry in the morning)

Ghrelin learns your eating pattern. Eat lunch at 12 daily, and ghrelin starts rising around 11:30.

2. What Happens in the Brain

When ghrelin reaches the hypothalamus:

• Activates NPY/AgRP neurons → appetite UP

• Suppresses POMC neurons → satiety signals BLOCKED

• Stimulates dopamine system → reward craving for food increases

Ghrelin doesn't just signal hunger — it signals "eating will feel amazing." Craving chicken during a diet isn't weak willpower, it's hormones hijacking your brain's reward circuit.

3. Ghrelin's Partner: Leptin

Obese individuals develop leptin resistance — the "stop eating" signal gets ignored while ghrelin keeps screaming "eat more."

The Diet Paradox

Calorie restriction triggers:
1. Ghrelin surge (~24% increase)
2. Leptin drop
3. Metabolic rate decrease

This triple defense is why diets fail biologically. "Beat hunger with willpower" means fighting your entire hormone system. Ghrelin stays elevated for at least 1 year after dieting stops (Sumithran et al., 2011). That's why yo-yo happens.

Why Obesity Drugs Are Getting Attention

Medicine now acknowledges you can't willpower your way through ghrelin-leptin dynamics. Drugs like Wegovy and Mounjaro (GLP-1 receptor agonists) intervene at the hormonal level, reducing hunger itself rather than asking you to resist it.