Collagen is the most abundant protein in the human body, accounting for approximately 25% to 35% of its total protein content. This fibrous structural protein provides the scaffolding for all connective tissues, including the skin, bones, tendons, and ligaments. Like all proteins, collagen is constructed from chains of amino acids linked in specific sequences. Among these amino acids, glycine stands out due to its high concentration and specific structural contribution.
The Foundational Role of Glycine in Collagen Structure
Glycine is exceptionally prevalent in the collagen molecule because its presence is mandatory for the protein’s characteristic shape. Collagen exists as a triple helix, a unique structure where three polypeptide chains are tightly wound around one another. This tight coiling is only possible if one of the amino acids is small enough to fit into the restricted space at the center of the helix.
Glycine is the smallest of all 20 amino acids, possessing only a single hydrogen atom as its side chain, making it the perfect fit for the restricted space. The sequence of amino acids in collagen is highly repetitive, following a pattern of Glycine-X-Y, where glycine is positioned at every third residue along the chain. Without this precise, recurring placement of glycine, the collagen helix would be unable to form or maintain its structural integrity, leading to tissue weakness.
Quantifying Glycine in Collagen Protein
The unique structural requirement of the triple helix means that glycine is the most abundant amino acid in collagen by a significant margin. Depending on the source and type of collagen (such as Type I found in skin and bone, or Type II in cartilage), glycine accounts for approximately 20% to 33% of the total amino acid residues. This means that roughly one-third of the entire collagen protein is composed of this single, small amino acid.
Translating this percentage into practical terms for a consumer, a standard 20-gram serving of collagen peptide powder typically yields a substantial amount of glycine. If a collagen supplement is 20% glycine by weight, a 20-gram serving provides 4 grams of glycine. If the concentration is closer to 25% by weight, that same 20-gram serving delivers 5 grams of pure glycine.
The concentration of glycine is relatively consistent across common collagen sources, such as bovine, marine, and chicken. This consistency exists because the underlying molecular structure of the triple helix is identical across these animal sources. The fundamental need for glycine at every third position dictates its high concentration, regardless of whether the product is hydrolyzed bovine collagen (Type I) or chicken sternum collagen (Type II).
Why Glycine Matters for the Body
Beyond its role in building connective tissue, glycine supports numerous independent physiological processes. It is a precursor molecule required for the body’s synthesis of other compounds. One of its primary functions is serving as one of the three amino acids needed to produce glutathione, a powerful antioxidant that protects cells from oxidative damage. Glycine also plays a role in energy metabolism, as it is utilized in the production of creatine, a compound that supports muscle function and strength.
Glycine also acts as an inhibitory neurotransmitter in the central nervous system, where it can promote a calming effect. This neurotransmitter function is one reason why supplemental glycine has been associated with supporting improvements in sleep quality.
The amino acid also aids the body’s natural detoxification processes, particularly in the liver. Glycine facilitates the conjugation of bile acids, which is a necessary step for the proper absorption of fats and fat-soluble vitamins.