Glycine — the amino acid modern diets forgot
The body can synthesise glycine, so it's classified as non-essential. But synthesis covers only 3g per day. Metabolic demand is 10–15g. The gap is dietary.
nutrition
The primary dietary source of glycine historically was connective tissue, bone broth, skin, and organ meats — everything systematically removed from modern diets in favour of muscle meat. Muscle meat is high in methionine. Glycine is required to safely metabolise methionine. A high-protein diet from muscle meat alone — exactly what most fitness-oriented people eat — increases the glycine deficit.
Glycine is required for glutathione synthesis (the body's master antioxidant), collagen production, bile acid conjugation, creatine synthesis, and formation. At 3g before bed, it has measurable sleep-improving effects through glycine receptors in the suprachiasmatic nucleus — the brain's master circadian clock.
Best dietary sources: bone broth, collagen powder, skin-on poultry, gelatinous cuts of meat
High methionine intake (muscle meat, eggs) increases glycine demand — the balance matters
3g glycine before bed: clinically supported for reduced sleep onset time and improved sleep quality
Glycine is required for glutathione — the body's primary intracellular antioxidant