I picked this up listening to an interview with Richard Wrangham, who wrote Catching Fire: How Cooking Made us Human.
In talking about digestibility of foods, he brought up the fact that - and this was news to me - although meat and protein that reaches the large intestine is consumed before it "exits" your system, it's consumed by intestinal fauna that convert it to to chemicals which are not disgestible by people and get passed. In other words, protein that gets past your small intestines never gets taken up by your body!
This means that measuring protein that's passed by your system doesn't tell you how much protein YOU digested. You need to measure it higher up, where it exits the small intestines, which is nearly impossible with normal people!
On the plus side, scientists can gather data from people who've had the the misfortune of losing their large intestines and have had an illiostomy. These people have a bag that collects everything that exits their small intestine. Think colonostomy bag, but attached much higher up. It's an incredible boon for The Scientists - ready-made intestinal output, pre-bagged!
So a bunch of Belgian gastro-intestinal physiologists were feeding people various cooked and uncooked items, and measuring what comes out undigested. And what did they find?
Nearly half the protein in raw eggs passes undigested! Depending on the person, 55 to 64% of the protein gets digested. But if the eggs are cooked, 94% of the protein is digested. That's a big difference.
Proteins that are cooked undergo some denaturing by the heat, which makes them easier to digest. It actually begins the digestion process... So it doesn't much matter how the eggs are cooked, just that they ARE cooked.
I'm wondering how much heat is necessary, and how much difference it makes... are the rare steak crowd depriving themselves of a lot of the protein they consume?