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.
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?