I’m reading Harold Mcgee’s On Food and Cooking in which he claims that despite the high nutritional content of an egg, laboratory animals have been shown to lose weight when eating raw eggs. It’s only in cooking that the nutritional goodness can be realized. The book states that this is due to the “antinutritional” proteins in the albumen which bind tightly to the vitamins and iron found in the whites. (These proteins are good for the developing chick because foreign microbes and bacteria attacking through the porous shell won’t be able to gain as good a foothold. It’s not explained how the chick is able to neutralize the proteins to get at the vitamins and such.)
Now, I’m confused because it was previously stated that the yolk, by far, is the part of the egg which contains most of the nutrients for the developing chick (and thus for us). Is it that the study I mention above feeds the test animals a mixture of whites and yolk, and there are lots of the “antinutritional” proteins to spare which will bind to goodies in the yolk and deprive the eater?
If the test animals were fed just yolks, would they no longer lose weight?
Are body-builders who drink raw eggs before a workout fooling themselves?
Similarly, it is said that the human body can extract very little of the iron and calcium from spinach.
It astonishes me that there so little dedicated research going on into human nutrition. And very little astonishes me anymore.
Like, how hard can it be to test people’s blood for iron, and then feed them spinach and test them again? The basic problem is that it would take a grant writer years to raise the millions of dollars necessary to make sure the test would withstand peer review.
There is a helluva lot of research going on into human nutrition. And yes the experiment would have to withstand peer review. That means controlling for a wide variety of confounding factors and variations which can easily result in noise that swamps any real signal in the data. That’s like quite hard. Then the issue becomes if the question is important or interesting enough to go after compared to other questions that can be asked. Spinach and iron? Meh. Enough good reasons to include spinach a part of your wide variety of vegetables that we know are a good idea that knowing precisely how much of an iron source it is is not too important to go after. Raw eggs? Already plenty of good reasons to not eat 'em.
The general principle though seems to fairly well established: cooking increases nutrient availability in many foods. What that means as good or bad though is harder to parse. Is that bad to absorb less nutrition directly? Good because we absorb less calories too? Good because it gets into the lower gut and feeds our beneficial bacteria which then feed us and send out all sorts of good messengers and compounds? Different answers depending on your individual genome or depending on other dietary variations? Or what?
These are not simple questions despite the simple messages some web sites promote.
Cooking denatures proteins and chemically alters other nutrients. It’s likely that the amino acids in proteins will be most efficiently absorbed when the complex 2nd, 3rd and 4th order structures are first denatured into simple strings of amino acids.
It is true that there is protein in egg whites, avidin, that binds to the important vitamin biotin (aka vitamin B7) and makes it less available. Cooking of the egg white denatures the avidin (and the other proteins present) and destroys its ability to bind biotin (as well as making all the egg white proteins more digestible), but the way eggs are often cooked, not all the avidin gets denatured. As I understand it, the avidin will not just bind any biotin in the egg itself, but, if the egg is eaten with other foods (or other things are still in the digestive tract), it will absorb any biotin that they might contain.
Fully cooked, denatured egg white, however, is a good source of protein and will not cause this problem. The avidin will be deactivated.
I have not heard that anything similar occurs with egg white and other vitamins (though I suppose it is possible), but the absorption of biotin by avidin is a real effect, and I believe there have been real cases of people getting sick due to biotin deficiencies caused eating too much raw egg white.
Denaturing does not necessarily involve hydrolisis, although both take part during cooking. Denaturing is the process of changing the protein’s 3D shape from its natural configurations (a protein can only do its job when it’s folded in a very specific way; denaturing is equivalent to handing a rolled-up string to a child). A denatured protein will be more accessible to the harsh pHs of the stomach and thin intestine, and to the lysic proteins therein, thus it will hydrolize more efficiently and be absorbed more efficiently (lactase is an example of a lysic protein: it breaks lactose into its two component monocarbohydrates).
The “chemically alters other nutrients” amount mostly to hydrolisis and oxidation.
Would it be possible to feed a person nothing but spinach for one day after an intestinal cleanse. Then test the iron content of the spinach he is eating as opposed to how much is left in his poop?
First, my reference to the 2nd, 3rd and 4th level structures was precisely the same thing as saying 3D structure. For example 2nd level consists of alpha helices and beta sheets. I don’t know if you think you stated something different or there was a reason for confusing the issue by just restating what I said.
Second, while not a chemist, just a quick search on chemical changes of cooking revealed a vast amount more than ‘hydrolysis and oxidation’ - for example.