What Happens to Collagen You Drink?

You may hear that collagen supplements are “pointless” or “have no effect.” Here are the common reasons, side by side with what research shows.

Collagen is one of the proteins that make up the body. Like other proteins, collagen that is eaten or drunk is digested in the stomach and intestines into peptides (short chains of amino acids) and amino acids before it is absorbed. So collagen you drink does not become the body’s collagen in its original large form.

The main reason people call it pointless is this breakdown. However, as the next section shows, research has found that some of it enters the blood as small peptides without being fully broken down.

Collagen is rich in an amino acid called hydroxyproline (Hyp). Using it as a marker, researchers can see what form collagen takes in the blood after drinking it. Studies by Japanese universities and companies report the following.

Cell experiments on the peptides found

The 2011 study reported that Hyp-Gly was less easily broken down by blood enzymes than Pro-Hyp, and in experiments with mouse fibroblasts (cells that make collagen), it increased cell growth more than Pro-Hyp. These are cell experiments; whether the same happens in the human body must be tested separately.

All these studies were small and measured blood after ingestion. Peptides entering the blood and changes occurring in the body are separate questions. Researchers from a food company took part in the 2007 and 2010 studies.

One way to compare protein quality is PDCAAS (Protein Digestibility-Corrected Amino Acid Score). By this method, collagen is classed as an incomplete protein because it lacks tryptophan, one of the essential amino acids the body cannot make.

On the other hand, a 2019 study calculated that, based on a standard American diet, up to 36% of daily protein could be replaced with collagen peptides while still meeting essential amino acid requirements. The amounts used in past studies (2.5–15 g per day) fall within that range. The authors include company researchers and a researcher who provides research services to a maker of supplements containing collagen peptides.

In short, collagen alone cannot cover protein needs, but added to an ordinary diet it does not upset the balance of protein.

Is drinking collagen pointless?
That cannot be said definitively. Ingested collagen is digested, but some enters the blood as small peptides.

Does collagen you drink become the body’s collagen as is?
No. It is first broken down into amino acids and small peptides, then absorbed.

How long do the peptides stay in the blood?
A 2005 study reported that they peaked 1–2 hours after ingestion and fell to half the peak at 4 hours.

Do we get collagen from ordinary food?
Japanese women are estimated to take in about 2 g of collagen a day from their diet.

How much is used in studies?
Past studies have used about 2.5–15 g per day.