The serotonin gate

Tryptophan, the building block of serotonin, has to squeeze through a gate it shares with other amino acids. Your meal decides how crowded it gets.

Tryptophan competes with other large neutral amino acids at the blood-brain barrier; insulin after a carb-rich meal moves competitors into muscle Bloodstream Blood-brain barrier Brain shared gate Tryptophan's share at the gate Muscle Insulin pulls competitors into muscle Tryptophan Competing amino acids From plate to sleep Tryptophan 5-HTP Serotonin Melatonin needs iron needs vitamin B6 needs darkness

Schematic illustration; particle ratios are simplified. Mechanism: Fernstrom & Wurtman, Science 1971; human meal data: Wurtman et al., Am J Clin Nutr 2003.