Collagen peptides are small protein fragments made from animal collagen, typically sourced from cow hides, fish skin and scales, or pig skin. They’re produced by breaking down the long, tough collagen protein into shorter chains that dissolve easily in liquid and are small enough for your body to absorb. At the molecular level, collagen peptides have a distinctive amino acid profile dominated by three building blocks: glycine, proline, and hydroxyproline.
The Amino Acid Profile
What makes collagen peptides chemically unique is their lopsided amino acid composition. In a typical hydrolyzed collagen supplement, glycine accounts for about 22% of the total protein by weight. Proline makes up roughly 13%, and hydroxyproline (a modified form of proline found almost exclusively in collagen) contributes about 12%. Together, these three amino acids represent nearly half the entire protein content.
This is unusual. Most dietary proteins spread their amino acids more evenly and contain meaningful amounts of all nine essential amino acids. Collagen peptides do not. They’re low in or completely missing certain amino acids your body can’t make on its own, which is why collagen supplements aren’t a replacement for complete protein sources like meat, eggs, or legumes. What they do provide is a concentrated dose of the specific amino acids your body uses to build and maintain its own collagen in skin, joints, tendons, and bones.
Where the Collagen Comes From
The raw material for collagen peptides is always connective tissue rich in collagen protein. The source determines which types of collagen end up in the final product.
- Bovine (cow): Derived from hides and bones. Contains type I collagen, the most abundant form in human skin and bones, along with type III collagen, which provides strength and flexibility to soft tissues like blood vessels and organs.
- Marine (fish): Sourced from fish skin and scales. Rich in type I collagen specifically, which makes it a popular choice for skin, hair, and nail supplements.
- Porcine (pig): Extracted from pig skin. Structurally similar to human collagen and widely used in both supplements and medical applications.
All three sources produce peptides with similar amino acid profiles. The practical differences come down to dietary restrictions, allergen concerns, and which collagen types you’re looking for.
How Collagen Becomes Peptides
Intact collagen is an enormous, rigid protein. Its molecules twist together in a tight triple-helix structure reinforced by chemical cross-links, making it resistant to digestion. You can’t just eat raw connective tissue and expect your gut to break it down efficiently. Manufacturing collagen peptides solves this problem in three stages.
First, the raw material (hides, bones, or fish skin) is pretreated, usually with an acid or alkali solution, to loosen the protein structure and remove non-collagen components. Next, the collagen itself is extracted, often through heating, which partially unwinds the triple helix and produces gelatin. Finally, enzymes are applied to cut the gelatin chains into much smaller fragments. This enzymatic hydrolysis is the industry standard because it produces consistent, small peptides without harsh chemicals. The resulting powder dissolves in hot or cold liquid and has little to no taste.
How Your Body Absorbs Them
One reason collagen peptides are hydrolyzed into small fragments is absorption. When you drink a collagen supplement, your digestive system doesn’t break every peptide down into individual amino acids. Some fragments, particularly short chains of two or three amino acids, survive digestion and enter your bloodstream intact.
Research published in the Journal of Agricultural and Food Chemistry traced what happens to a key collagen fragment (a three-amino-acid chain of glycine, proline, and hydroxyproline) after ingestion. Enzymes on the surface of intestinal cells clip off the glycine, leaving a two-amino-acid fragment of proline and hydroxyproline. This smaller piece is then transported through the intestinal wall by a dedicated peptide transporter and resists further breakdown. It appears in blood plasma within 15 minutes and has been detected in skin tissue. This is notable because it means collagen peptides don’t just supply raw amino acids. Some bioactive fragments reach target tissues in a form your body may use as signaling molecules to stimulate its own collagen production.
Plant-Based Collagen Alternatives
True collagen is an animal protein. Plants don’t produce it. However, researchers have developed recombinant collagen using genetically engineered microorganisms. Yeast (specifically Pichia pastoris) and bacteria (like E. coli) can be programmed with human collagen genes to produce collagen-like proteins through fermentation.
The challenge is replicating collagen’s structure. Natural collagen requires a chemical modification called hydroxylation to form its signature triple helix and remain stable. Bacteria and yeast don’t naturally perform this modification well, so researchers must co-express additional enzymes alongside the collagen gene. Mammalian cell systems produce proteins closest to natural human collagen, with proper structural modifications and high biological activity, but they’re expensive and difficult to scale. Even in the best lab-engineered versions, achieving the same level of hydroxylation as animal-derived collagen remains a technical hurdle. Most “vegan collagen” supplements currently on the market contain collagen-boosting ingredients like vitamin C and amino acids rather than actual recombinant collagen protein.