Glycosaminoglycans from food

Cartilage is not mostly collagen by function — it is collagen fibres holding a water-swollen gel of glycosaminoglycans, and it is the gel that resists compression. So the second question about any collagen-rich food is what glycosaminoglycans it delivers: chondroitin sulfate, hyaluronic acid, keratan sulfate, dermatan sulfate.

The answers range from "surprisingly good" to "nobody has ever looked."

Chondroitin sulfate survives cooking

This is the genuinely encouraging finding. Chondroitin was extracted from ordinary chicken leg bone soup and compared against chondroitin obtained enzymatically from the same bones. The soup-derived molecule averaged 35.81 kDa, the enzymatic reference 37.18 kDa, and infrared spectroscopy and HPLC found no significant structural difference.

That is a roughly 4 percent difference in molecular weight. Chondroitin comes through a simmer essentially intact, which is not obvious in advance — plenty of food polysaccharides do not.

It also does something. In the one bone-broth animal study with a skeletal endpoint, chicken-vegetable broth was fractionated by ion-exchange chromatography, and the fraction containing hyaluronan and chondroitin sulfate was the one that most inhibited osteoclast differentiation. Both the whole broth and that fraction raised bone mineral density and bone volume in ovariectomised rats. Bone, not cartilage — but the constituents were identified rather than assumed.

Then the arithmetic

A carcass survey measured how much chondroitin a broiler chicken actually contains. The answer: about 1.9 g in the entire 1.66 kg bird. Keel cartilage, the part usually named as the good source, held under 10 percent of it; most is distributed through the limb bones and joints.

The trial dose of chondroitin is 800–1200 mg per day. So a whole chicken contains one to two days' worth — if you extracted all of it, which cooking does not. The one measurement of transfer into soup reports a 0.14 percent process yield.

There is no plausible reading in which a bowl of stock delivers a studied chondroitin dose.

What the chondroitin dose actually buys

Worth knowing before chasing it. The Cochrane review pooled 43 trials and just over 9,000 participants. Its highest-quality result — high level of evidence, low risk of bias — is that 53 of 100 people on chondroitin achieved a 20 percent pain reduction against 47 of 100 on placebo. An absolute difference of six percentage points.

Joint space width loss was 4.7 percent less than placebo, also high quality. Serious adverse events were lower than placebo.

That is a real, replicated, small effect at a pharmaceutical dose. The reviewers add the sentence that matters most: benefits "were uncertain when we limited data to studies with appropriate allocation concealment, or large samples, or studies without pharmaceutical funding."

Hyaluronic acid: present, and fragile

Hyaluronan was the co-constituent in the active bone-broth fraction, so it is demonstrably in there. Two problems follow.

It is heat-labile — hyaluronic acid depolymerises readily in hot water, and long simmering should be expected to fragment it substantially. Nobody has measured how much survives.

And for chicken feet specifically, the only published hyaluronic acid figure comes from a paper that has since been retracted. This guide does not cite it, and the honest position is that the hyaluronic acid content of chicken feet is unknown.

Keratan and dermatan sulfate: nobody has looked

Keratan sulfate is a major glycosaminoglycan of aggrecan — it is genuinely part of the cartilage people are trying to eat. Dermatan sulfate decorates decorin and biglycan in tendon and skin.

Neither has ever been measured in any broth or stock. Not measured and found low — never looked for. There is likewise no oral keratan sulfate trial in any species, and no oral dermatan sulfate trial with a joint endpoint.

This distinction is load-bearing and this guide will keep making it: unmeasured is not the same as absent. Everything written anywhere about "the full spectrum of glycosaminoglycans in bone broth" is extrapolation from chondroitin.

The glucosamine mistake

One correction worth making explicitly, because the claim is everywhere and it is wrong at the first step.

Chondroitin sulfate contains no glucosamine. Its repeating disaccharide is glucuronic acid plus N-acetyl-galactosamine. Glucosamine occurs in hyaluronan, keratan sulfate and heparan sulfate — not chondroitin. So "long simmering breaks chondroitin down and releases glucosamine" is not a dosing question, it is a chemistry error.

Separately, liberating free glucosamine from the glycosaminoglycans that do contain it requires strong acid at length — the industrial process uses molar hydrochloric acid near boiling for hours. A tablespoon of vinegar in a stockpot is two to three orders of magnitude away, and a weak acid rather than a strong one.

There is no measurement of free glucosamine in bone stock, chicken feet, or any cooked food. Not low — unmeasured, and mechanistically implausible.