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I saw the following claim in several places:

At Raw Glow

Cooking meat changes the molecular structure of some of its proteins, rendering them unusable by the body and making cellular healing, reproduction and regeneration difficult. The protein molecules become bound, making them harder to digest. Up to 50% of cooked proteins that one eats will coagulate and cross-link. Cross-linking of proteins is associated with Alzheimer’s disease.

Because of coagulation, the protein is 50% less assimilable, as research showed at the Max Planck Institute for National Research in Germany. This means that a person needs to eat twice as much protein if it is cooked as opposed to raw.

At Sacred Source Nutrition

According to the Max Planck Institute, cooking foods coagulates at least 50% of the protein[ii], making them less bio-available to the body.

I also heard this in the film "Food Matters".

I'm having a very hard time believing this, as I would expect denaturation of proteins to help with digestion, as it makes it easier for proteases to cut them up into amino acids. The idea that cooking proteins hinders their digestion sounds rather far-fetched to me. But I was unable to find the study from the Max-Planck Institute that is referenced, none of the articles directly link it.

Does this study exist and does it support the claim? Is there any other data on the effect of cooking on the digestibility and bioavailibity of proteins?

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Well, we could start by the fact that there’s no “Max Planck Institute for National Research” but that would be facile. – Konrad Rudolph Feb 26 at 13:34
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It would seem to go against a basic tenant in anthropology that cooking meat enabled humans to advance by making food easier and less energy intensive to digest. Although, to be fair, the linked article is talking about plant based protein not animal based. – Paul Turnbull Feb 26 at 15:00
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I'll try and post more extensively later, but the claim is basically a false cause. Of course cooking denatures proteins, that is the goal, with bacteria killing in mind. Your digestive system breaks all of those proteins down anyway, so converted "cooked" proteins are no big deal. Now, if the argument was about what protein and amino ratios are present, then there is something to this, but otherwise it is bunk. Also, the Food Matters doco is made by some pseudo-science scare-mongerers, so I doubt its accuracy or science basis. – Tim Scanlon Feb 26 at 21:18

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