Egg whites can be a great source of protein, but raw egg whites may interfere with nutrient absorption. Nutrition Diva cracks the case.
Q. "I include 1/2 cup of pasteurized raw egg whites in my smoothie every morning. (I need a lot of protein in the mornings or I don't make it to lunch). But I was warned that eating too many raw egg whites can cause B-vitamin deficiencies. How much is too much?"
A. Uncooked egg whites contain a protein called avidin, which binds tightly to the vitamin biotin and prevents its absorption. So, it's not all B-vitamins that we're worried about here - just biotin.
Heat largely deactivates avidin, so this is not a concern with cooked eggs. But eating too many raw egg whites could potentially lead to a biotin deficiency. You'd have to eat a lot of egg whites for a long time to be at risk. Then again, 8 raw egg whites every single morning is a lot of egg whites! Biotin deficiency is very uncommon but signs can include a rash around the eyes, nose, and mouth as well as unexplained hair loss.
What Are Good Sources of Biotin?
Eating raw egg whites in the morning shouldn't interfere with absorption of biotin from meals eaten later in the day. As long as you're getting some biotin at your other meals, you should be OK. You get small amounts from a wide variety of foods, but liver, fish, avocado, peanuts, sunflower seeds, and (ironically!) egg yolks are all particularly good sources of biotin.
Using an egg-white-based (or any other) protein powder instead of raw egg whites would be another way of getting around this potential problem.
See also: What’s the Best Protein Powder?