Collagen Peptides

Modest but repeated RCT support for joint pain, tendon properties, and skin elasticity. As a muscle-building protein it is inferior to whey, being low in leucine and missing tryptophan.

Collagen is the most abundant protein in your body and one of the worst you can eat. Judged as a protein source it is genuinely poor: low in leucine, entirely missing tryptophan, and scoring near the bottom of every protein quality scale. If someone recommends collagen for building muscle, they have the biochemistry backwards.

Which makes the actual evidence more interesting, because it points somewhere else entirely. Hydrolysed collagen breaks into small peptides — prolyl-hydroxyproline chief among them — that survive digestion intact, show up in the bloodstream, and preferentially accumulate in skin and connective tissue. The current best guess is that they work as signals rather than bricks: fragments of collagen circulating in blood look, to a fibroblast, like tissue damage worth repairing.

The outcome literature is modest but persistent. Joint pain in athletes and people with mild osteoarthritis improves in several controlled trials. Skin elasticity and hydration improve in a reasonably consistent set of RCTs, mostly industry-funded, which is worth knowing. Tendon and ligament work is the newest and most intriguing thread — gelatin or collagen taken with vitamin C about an hour before loading the tissue appears to increase collagen synthesis markers, though the trials remain small and the performance endpoints thin.

There is one respectable muscle finding, and it comes with an asterisk: in sarcopenic older men, collagen peptides plus resistance training beat training alone. In that population almost any protein would likely have done the same, and probably better.

So the sensible position is a narrow one. If your interest is tendons, joints, or skin, 10-15 g daily for at least eight weeks is cheap, safe, and has a plausible if unspectacular case. If your interest is muscle, buy whey — and if you take collagen anyway, count it as separate from your protein target rather than toward it.

How it works

Hydrolysis breaks collagen into di- and tripeptides such as prolyl-hydroxyproline, which survive digestion, appear in blood, and accumulate in skin and connective tissue. There they appear to act as signalling molecules that stimulate fibroblast collagen synthesis, rather than as raw building blocks.