Collagen in foods

Short answer

Collagen is the most abundant protein in mammals and is found in animal tissues. ^[4] Foods such as bone broth, gelatin and skin-cartilage supply collagen precursors (glycine, proline, hydroxyproline); however, the amount in bone broth varies greatly with the recipe, and a standard bone broth has not reached the levels in a reference collagen supplement. ^[1] In the studies reporting that dietary collagen “increases” body collagen, this was followed indirectly through blood amino acids and synthesis markers, not through skin or joints. ^[2]

Which foods contain collagen?

Collagen is a protein family with 28 members in vertebrates. ^[4] The sources that appear as food are products obtained from the connective tissue, skin, cartilage and bone of these animals: bone broth, gelatin and the raw materials of collagen supplements.

In supplement studies, gelatin hydrolysates obtained from tissues such as pig skin, chicken feet and cartilage have been used; after volunteers drank these hydrolysates, peptides containing hydroxyproline, most notably Pro-Hyp, were measured in their blood. ^[3] However, eating these tissues as food does not supply the same amount and form as drinking a hydrolysate, and no study measuring peptide levels after an eaten portion is included in the evidence reviewed.

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How much collagen precursor does bone broth supply?

Alcock and colleagues measured the levels of glycine, lysine, proline, leucine, hydroxyproline and hydroxylysine in commonly consumed bone broth preparations. Commercial and laboratory-prepared samples were examined, with standard and nonstandard recipes. In bone broth made with a standard recipe, hydroxyproline, glycine and proline (p = 0.003) and hydroxylysine, leucine and lysine (p = 0.004) were significantly lower than what the 20 g per day reference collagen supplement provides. In nonstandard recipes the amino acid content was highly variable; the highest values were in the types prepared in cafés. In standard recipes, commercial bone broths were lower than home-prepared ones. There was no difference between different batches of the same standard recipe. ^[1]

The authors’ conclusion is this: even if intake of collagen precursors supports new collagen synthesis, bone broth is not expected to be a reliable source of the key amino acids. ^[1] This is a laboratory measurement; it is not a study testing the effect of bone broth on human outcomes.

Does gelatin increase collagen synthesis?

In the study by Shaw and colleagues, 8 healthy men received 5 g or 15 g of gelatin enriched with vitamin C, or placebo, in a crossover double-blind design. With increasing gelatin amount, circulating glycine, proline, hydroxyproline and hydroxylysine increased, peaking at 1 hour. In engineered ligaments fed for 6 days with serum taken before and 1 hour after gelatin intake, collagen content increased and mechanical properties improved. In participants who took 15 g of gelatin 1 hour before exercise, the amino-terminal propeptide of type I collagen (PINP) in the blood doubled; this is a blood marker showing that collagen synthesis increased. ^[2]

The authors interpreted this as “adding gelatin to an intermittent exercise program may increase collagen synthesis”; they did not measure injury prevention. The study was supported by a national institute on aging grant and university and sports institute grants; the funders had no role in design and analysis, and the authors reported no conflict of interest. ^[2] It is an 8-person, short-term study and did not measure skin or joint outcomes.

Why does swallowing collagen not mean “direct collagen”?

In the building of collagen in the body, amino acids are bound into proα chains inside the cell; modifications such as hydroxylation of proline and lysine are made afterward. ^[4] That is, the body does not place a protein from food in position unchanged; swallowed collagen is broken down, and peptides containing hydroxyproline are measured in the blood. ^[3]

The collagen protein itself is also not a complete protein. The authors of a study in older women reported that the digestible indispensable amino acid score of collagen protein is 0 because it contains no tryptophan; in the study, when 30 g of collagen peptide was taken twice a day for 6 days, long-term muscle protein synthesis did not rise significantly above basal levels (in the acute measurement the increase was only in the exercised leg); the authors wrote that they also saw no effect of nutrition on the synthesis rate of muscle collagen (a basal biopsy could not be taken for this measurement). ^[5] A food rich in collagen therefore does not take the place of the main protein source.

What do vitamin C, copper and other helpers do?

Vitamin C: According to the NIH, vitamin C is required for collagen biosynthesis; in deficiency (scurvy) collagen synthesis is impaired and connective tissue weakens. Symptoms of scurvy can begin within a month with intake below about 10 mg per day. ^[6] This is information about a role and a deficiency; it is not shown that extra vitamin C increases skin or joint collagen in a person with adequate levels.

Detailed guideVitamin C: functions, deficiency and supplement evidence→ Detailed guideWhich foods contain vitamin C?→

Copper: According to the NIH, copper is a cofactor of copper-containing enzymes (cuproenzymes) that function in many processes, including connective tissue synthesis; deficiency is uncommon in humans; according to animal and human studies, connective tissue disorders, osteoporosis and other bone defects can be seen in deficiency. ^[7] This is not information of the type “extra benefit when there is no deficiency.”

Zinc: The matrix metalloproteinase (MMP) enzymes that break down collagen are zinc-dependent. ^[4] The simplification “zinc means more collagen” is therefore misleading; zinc is a separate topic, and its deficiency and food sources are covered in its own guide.

Detailed guideZinc: functions, deficiency and supplement evidence→

Glycine and proline: In the triple helix of collagen, every third position is glycine, and the helix is rich in proline and hydroxyproline. ^[4] No randomized study showing that high intake of these amino acids increases collagen synthesis is included in the evidence reviewed; what was observed in the Shaw study is that these amino acids rise transiently in the blood with gelatin. ^[2]

Why is the evidence for dietary collagen indirect?

The studies reported measure amino acid levels in the blood, collagen synthesis markers or changes in laboratory-prepared tissues; they do not measure skin, joint or bone outcomes. These measurements show a possibility but are not evidence of clinical benefit. Clinical outcome studies of collagen supplements (skin, joint, bone) are covered, study by study, on a separate page.

Detailed guideCollagen benefits: which claims are supported?→ Detailed guideCollagen guide: what it is, how it is processed, what EFSA said→ Detailed guideCollagen types and hydrolyzed collagen→

This guide does not give personal nutrition or supplement recommendations.