Also see: Thyroid peroxidase activity is inhibited by amino acids Whey, Tryptophan, & Serotonin Tryptophan, Fatigue, Training, and Performance Carbohydrate Lowers Free Tryptophan Protective Glycine Gelatin > Whey J Biosci. 2009 Dec;34(6):853-72. A weak link in metabolism: the metabolic capacity for glycine biosynthesis does not satisfy the need for collagen synthesis. Meléndez-Hevia E, De Paz-Lugo … Continue reading Gelatin, Glycine, and Metabolism