The claimEvidence B · meta-analysis
Collagen peptides 'rebuild' your skin/joint collagen
The evidence
Oral peptides are degraded to amino acids in the gut; this is the 'eat pork knuckle to feed your skin' fallacy.
Why the claim spreads
'Eat the thing to become the thing' is intuitive (and wrong about how digestion works); beauty brands market the story hard.
The mechanism, in brief
Collagen is the scaffolding that holds the body up. The structure of skin, bone, cartilage, tendons, ligaments, vessel walls and the white of the eye is mostly built from it. It is also the most abundant protein in the body, about 25–30% of all protein.
Sources (1)
- Khatri, M., Naughton, R. J., Clifford, T., Harper, L. D., & Corr, L. (2021). The effects of collagen peptide supplementation on body composition, collagen synthesis, and recovery from joint injury and exercise: a systematic review. Amino Acids, 53(10), 1493-1506. Systematic review of 15 RCTs (from 856 articles screened) combining collagen peptides with exercise: 12 in recreational athletes, 2 in elderly participants, 1 in untrained pre-menopausal women. Outcomes: joint pain and recovery from joint injury, body composition, muscle soreness and recovery, muscle protein and collagen synthesis; no skin endpoint, and the abstract reports no pooled effect estimate. Collagen synthesis rates were elevated with 15 g/day, with no significant effect on muscle protein synthesis vs isonitrogenous higher-quality protein (abstract, PMID 34491424; full text, PMC8521576).