[gamblor956]

Not a surprise. Collagen is important for healing skin wounds, and vegans get none from their diet. (Collagen is just a protein, so it can be generated by the body, but it's easier for the body to simply take collagen from dietary sources.)

[subungual]

Do you have a source for this? As far as I know, there is no way for the body to uptake and employ collagen directly. It needs to be broken down into smaller peptides, absorbed, and rebuilt, just like any other protein.

[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?

[Metacelsus]

>it's easier for the body to simply take collagen from dietary sources.

Digestion doesn't work like that. Any ingested collagen is broken down to amino acids like all other proteins. Then the amino acids are re-polymerized into collagen.

[gamblor956]

Digestion doesn't work like that. A great deal of food is not fully broken down by digestion. In fact, many functions of the human body rely on various nutrients/whatever surviving their passage through the gut.

Most, but not all collagen is broken down into collagen peptides in the gut. Most of those collagen peptides are then broken down into amino acids. But not all collagen peptides are broken down, and the peptides that remain can enter the bloodstream where they can be utilized as needed.

(The collagen that doesn't get broken down in the gut tends to come out the other side of the digestive tract intact, because unlike collagen peptides, collagen is too large to enter into the bloodstream and there are no organs after the intestines that can make direct use of collagen.)

[souprock]

That right there would be surprising and disturbing. Collagen that shows up in the diet could arrive with subtle flaws.

Wikipedia: "as of 2011, 30 types of collagen have been identified"

Besides getting the wrong type, it could just be damaged. It also seems like an awfully big molecule to pass from the digestive tract to the blood. If that can pass through, then many poisons would also pass through.

Collagen is bigger than some viruses.