Modern Diet

An average tender steak contains only about 1–3% collagen, making it a poor glycine source relative to body needs. Historically, humans ate nose-to-tail, regularly consuming collagen-rich tissues such as skin, cartilage, connective tissue, tendons, ligaments, and bones. Even people following meat-heavy or carnivore-style diets may be low in glycine if they eat mostly steak and avoid collagen-rich nose-to-tail foods. Vegans, many children, and older adults are particularly likely to be deficient in glycine.