Collagen is the main structural protein of connective tissue: skin, tendons, cartilage, bone matrix. When cooked (denatured), collagen becomes Gelatin. Ray Peat favors collagen and gelatin to offset the methionine- and tryptophan-heavy profile of muscle meat, supporting Liver function and calmer metabolism.[1]

Food forms

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  • Collagen: native protein in raw connective tissue (tough when unhydrolyzed)
  • Gelatin: heat-denatured collagen; gels when cooled
  • Collagen hydrolysate: enzymatically broken peptides; same amino acid profile, no gel

All are glycine-rich relative to steak or chicken breast.

Ray Peat

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Gelatin (the cooked form of collagen) makes up about 50% of the protein in an animal, but a much smaller percentage in the more active tissues, such as brain, muscle, and liver.

— Ray Peat

[2]

When we eat animal proteins in the traditional ways (for example, eating fish head soup, as well as the muscles, or "head-cheese" as well as pork chops, and chicken-foot soup as well as drumsticks), we assimilate a large amount of glycine and gelatin.

— Ray Peat

[3]

Modern diets under-consume connective-tissue proteins relative to muscle meat, skewing amino acids toward thyroid-suppressing tryptophan and cysteine.[4]

Aging and elasticity

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In rat tail tendon work cited in Peat's hormone writing, excess Estrogen reduces collagen elasticity; Progesterone is protective. That is experimental biology, not dietary collagen as hormone replacement. [5]

A 2025 trial isolated the three amino acids that make up collagen's repeating unit, glycine, proline, and hydroxyproline, in a 3:1:1 ratio (5000 mg glycine, 1700 mg proline, 1700 mg hydroxyproline daily in the human arm). In C. elegans the blend increased lifespan 6-27% across five trials, more than whole collagen did. In 20-month-old mice it preserved grip strength and lowered visceral fat over 6 months. In a 3-month human trial, skin texture rose from 59.9% to 65.1% and cheek hydration rose from 35.9 AU to 48.3 AU; the wrinkle-reduction trend did not reach significance. Over 6 months, epigenetic age fell by an average of 1.4 years, with a maximum reduction of 12.1 years in women and 8.9 years in men.[6]

Joint pain in athletes

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In a 24-week randomized, placebo-controlled trial of 147 collegiate athletes with activity-related joint pain, 10 g/day of collagen hydrolysate significantly reduced joint pain at rest and during walking, standing, and running/direction changes compared to placebo, most clearly in the subgroup with knee pain; benefits took up to 24 weeks to become apparent.[7]

Food sources

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Bone broth, oxtail, pig skin, gelatin powder, collagen supplements. See Gelatin and Glycine.

See also

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References

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  1. ↑ "Gelatin, stress, longevity," Ray Peat article
  2. ↑ "Gelatin, stress, longevity," Ray Peat article
  3. ↑ "Gelatin, stress, longevity," Ray Peat article
  4. ↑ "Gelatin, stress, longevity," Ray Peat article
  5. ↑ Lee CA, Lee-Barthel A, Marquino L, Sandoval N, Marcotte GR, Baar K, "Estrogen inhibits lysyl oxidase and decreases mechanical function in engineered ligaments," Journal of Applied Physiology. 2015;118(10):1250-7. doi:10.1152/japplphysiol.00823.2014. PMID 25979936.
  6. ↑ Dakhovnik A, Mantovani M, Knufinke M, et al. "A collagen amino acid composition supplementation reduces biological age in humans and increases health and lifespan in vivo," npj Aging. 2025;11:91. doi:10.1038/s41514-025-00280-7.
  7. ↑ Clark KL, Sebastianelli W, Flechsenhar KR, et al. "24-Week study on the use of collagen hydrolysate as a dietary supplement in athletes with activity-related joint pain," Curr Med Res Opin. 2008;24(5):1485-96. PMID 18416885.