I am not a raw egg eater (drinker?). I don’t plan to become one, regardless of the outcome of my research for this post. However, I heard a discussion about eating raw versus cooked eggs. The advocate of raw eggs used the argument that the proteins are more available to humans in the raw egg, which was therefore, better for you. From this comes two topics: why do people think that the proteins are more available and is there a difference between cooked and raw egg digestibility.
The most common argument I can find is that cooking denatures the proteins in the egg. Denaturing sounds bad right? We’re taking something natural and making it less so. However, it is something that our bodies have to do to make it possible to absorb proteins. Proteins are fairly complex molecules. They are made up of amino acids (there are 20 different ones that combine in different sequences and numbers to make many different proteins). Think of the amino acids as paper clips. The amino acids are linked together (with peptide bonds) to form chains. Connect all the paper clips together. Then due to the different chemistry of each protein, the protein will fold up on itself. For your body to absorb the protein it needs to be broken all the way down to the individual amino acids. This involves breaking a lot of bonds. Denaturing a protein is breaking the bonds that make the chain fold on itself. You are changing the nature of the protein in a way, but if you don’t, you can’t actually absorb anything and what goes in one end will come out the other, no benefit at all.
The idea then, that by denaturing the egg proteins is reducing their nutritional value doesn’t work because whether cooking does it, or your body does, the proteins have to go through the process if they are to be used by the body.
So, which proteins are more available to the body, cooked or raw? Evenepoel et al. (1998) examined this question and found that about 90% of cooked egg protein was digested, compared to around 50% for raw egg protein. This means that your body has the ability to absorb 40% more of the protein in a cooked egg than in a raw egg. In another study Evenepoel et al. (1999) looked at how much egg protein was excreted through waste processes (solid and liquid). Only 5% of cooked protein was excreted, while 35% of the raw protein was excreted.
More generally, Carmody and Wrangham reviewed multiple studies on the effects of cooking on the energy availability in food and found that cooking efficiently denatures proteins, which makes them more digestible and more available for use. Carmody, Weintraub, and Wrangham also conclude that cooking protein increases the availability of energy from the protein which subsequently impacts body mass (more calories = more body mass if the calories exceed what is required).
It isn’t that consuming raw eggs is bad (although there is increased risk for some pathogens), but the argument that denaturing proteins is bad and makes them somehow less available is false. Cooked eggs are a better source for protein and subsequent energy in the body.