[gamblor956]

Yes, I should have been more specific that collagen gets broken down into collagen peptides. I didn't think I needed to be that specific since it's like the difference between Calorie and calorie (i.e., the distinction is not relevant to the discussion on hand).

We know that the body can use collagen without digesting it first because collagen masks are used to heal burn victims. See, for example: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6565829/, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3081477/

Collagen is a protein. It is made up of several "peptides" referred to as "collagen peptides." When it is first digested, collagen is broken down into collagen peptides in the gut. The type of collagen determines the ratios of these peptides. Most, but not all of these collagen peptides get further broken down into amino acids in the gut. (Contrast to whey, which gets entirely broken down into amino acids.) However, a significant portion of collagen peptides can survive digestion, or leave the gut before they are digested. (Up to 10%, depending on the original source of the collagen.) The body can utilize these peptides directly to repair skin, because skin is mostly made of...collagen. The presence of collagen peptides simply lets the body go straight to creating collagen without having to wait while peptides are created from amino acids. (The body will still do that, but it's like starting a construction project with supplies on hand vs having to wait for supplies to arrive or be built.)

[subungual]

Maybe I wasn't specific enough here. When I said "smaller peptides," I should have instead written "free amino acids, dipeptides and tripeptides." The two papers you cited refer to topical application, but your statement in your first comment said that it is easier to get collagen from dietary sources. What I'm asking for is what size of peptide you're calling a "collagen peptide" and a source supporting a mechanism of absorption. Most references I find to "collagen peptides" are for unvetted dietary supplements.

There is not good evidence that peptides larger than 2-3 amino acids can be absorbed into circulation via the gut in more than trace quantities (1). Digested collagen will be rich in certain amino acids (glycine and proline in particular), but calling something as small as a di or tripeptide a "collagen peptide" seems like an oddly arbitrary choice. I am a medical student with significant background in biochemistry, so please don't feel the need to dumb it down for me when you explain.

1. https://www.cambridge.org/core/journals/nutrition-research-r...

[gamblor956]

Collagen peptides are some of the bioactive peptides referred to in your citation that are known to be capable of passing beyond the gut in more than de minimis quantities... (Though in this context, it's still a small amount of the collagen originally consumed, between 1-10%.)

See https://academic.oup.com/fqs/article/1/1/29/4791729 for a discussion of bioactive peptides.

[nate_meurer]

> However, a significant portion of collagen peptides can survive digestion, or leave the gut before they are digested. (Up to 10%, depending on the original source of the collagen.)

Do you have a source where I can read more about this?