So you’ve been told, over and over again, that egg whites are a great low-fat, high-protein alternative to whole eggs. Even the popular website LIVESTRONG.com has egg whites listed in their Easy to Digest High-Protein Food article saying:
Egg whites are a fairly easy way to add protein to any diet. Simply hard-boil a few eggs and eat them as a healthy snack. One large egg contains about 6 grams of protein. About 3.6 of those grams are found in the egg white. People watching their saturated fat or cholesterol intake should stick to egg whites.
LIVESTRONG.com used the Protein Digestibility Corrected Amino Acid Score (PDCAAS) to determine the inclusion of egg whites, which got a perfect score. The premise is that if the egg white got a perfect score, it can’t be hard to digest. But it’s not that simple:
[PDCAAS] does not take into account certain factors influencing the digestion of the protein and is of limited use for application to human protein requirements because what is measured is maximal potential of quality and not a true estimate of quality at requirement level.
And these are the factors influencing the digestion of the protein:
- amino acids that have passed through the final section of the small intestine will either be passed out of the body or absorbed by bacteria–but they will appear to have been digested.
- amino acids that are lost because their absorption is blocked by antinutrients are assumed to be digested by the PDCAAS system.
And now we get to the real meat of the issue. Egg whites contain proteins which block enzymes that are needed to digest the protein. These are the antinutrients which are assumed to be digested by PDCAAS.
Most people don’t know, and aren’t being told, that egg whites consist of proteins that are hard to digest. In fact, the most protein in an egg white comes from ovalbumin–and it’s the major offender. The other protein that blocks digestives enzymes is ovomucoid which accounts for 11% of the total egg white protein. That’s a total of 65% of the egg white protein that is not only not absorbed, but is hard on your digestive system.
- ovalbumin (54%) — blocks digestive enzymes
- ovotransferrin (12%)
- ovomucoid (11%) — blocks digestive enzymes
- ovoglobulin G2 (4%)
- ovoglobulin G3 (4%)
- ovomucin (3.5%)
- lysozyme (3.4%)
- ovoinhibitor (1.5%)
- ovoglycoprotein (1%)
- flavoprotein (0.8%)
- ovomacroglobulin (0.5%)
- avidin (0.05%)
- cystatin (0.05%)
So does this mean you should never eat egg whites? No. But you may want to stay away from or limit all egg-white concoctions. If you’re looking for protein, you’ll get more out of the egg yolk. And if you’re looking to lower your overall fat intake, try to look at the other foods you’re eating to see if you can decrease the amount of butter and oils.