Glycine: Collagen, Sleep, Methylation & Chronic Undersupply

Glycine is the simplest amino acid, but its biological roles are anything but simple. It makes up roughly one-third of collagen (the body's most abundant protein), serves as an inhibitory neurotransmitter, is required for glutathione synthesis, acts as a conjugation agent for detoxification, and is consumed in large quantities by the methylation cycle (creatine synthesis is the single largest consumer of methyl groups).

The Undersupply Problem

Emerging research suggests that glycine may be chronically undersupplied in modern diets. Endogenous glycine synthesis produces only about 3g/day, while estimated metabolic demand may be 10-15g/day. Ancestral diets included more glycine-rich connective tissue, bone broth, and organ meats. Modern muscle-meat-focused diets provide much less glycine relative to methionine, potentially creating a metabolic imbalance.

Sleep Research

Glycine (3g taken before bed) has been shown in clinical studies to improve subjective sleep quality, reduce time to fall asleep, and decrease daytime sleepiness without next-day grogginess. The mechanism involves glycine's action on NMDA receptors in the suprachiasmatic nucleus, lowering core body temperature — a signal that promotes sleep onset.

Food Sources

Bone broth, gelatin, collagen supplements, skin-on poultry, pork rinds, and connective tissue meats are the richest sources. For supplementation, glycine powder is inexpensive and has a mildly sweet taste.