You would not believe the functional deficiencies that I see in high caliber athletes that eat very well. Specifically in choline and biotin.
When I say "functional deficiencies" I'm not referring to a true iron deficiency anemia or megaloblastic anemia with b-vitamins. Those are quite rare in athletes. I am referring to the way that your body is actually utilizing the nutrients that you are consuming through food. In order for your body to use the nutrients, there are many biochemical steps that must happen, from absorption to transport, to translation into an active form.
Let's take Vitamin A as an example. Plant sources of Vitamin A come in the form of carotenoids like beta-carotene, lycopene, zeaxanthin, and lutein are found in vegetables and fruits in the yellow, orange, green, and red families. Things like squash, broccoli, pumpkin, carrots, tomatoes. These are all great sources of carotenoids.
Carotenoids are pre-cursors to Vitamin A. This means that our body first sees them in their carotenoid form from the food itself, and then begins its journey to becoming an active form of Vitamin A that we can use. Those plant-based carotenoids travel to the small intestine where pancreatic enzymes begin the process of being broken down into an active form of Vitamin A, called Retinol. These plant sources have to be converted to Retinol in order to be fully utilized by the body. The way to directly get Retinol in the diet is through animal sources - like Butter and Egg Yolks. Now there are actually genetic variants along this pathway that make this process less efficient, increasing the need for these colorful veggies on a daily basis, but that's for another post.
Choline and Biotin are not quite "vitamins" although they act similarly to the B-Vitamins, so they are often grouped in with the B's.
Choline is considered an "essential" nutrient because although our liver can make small amounts, we need to get most of it from our diets - therefore, it's "essential" to eat. Choline is extremely important for liver function, brain development, muscle movement, nervous system, and metabolism. As adults, we need about 400-600 mg of Choline per day, and the richest sources of choline are found in animal products; Eggs and Fish.
Almost half of an egg's protein comes from the yolk. All of the choline is found in the yolk of the egg - all 147 grams of it! An egg yolk is the most concentrated source of Choline in the American diet.
Biotin is also an "essential" nutrient that we need to get from food. It is important for the metabolism of fat, sugar, and proteins, cell signaling, and gene regulations.
Adults need 3 mcg of biotin per day. Biotin is also mostly present in animal proteins. All of the biotin in an egg is in the yolk! 10 mcg of it!
The bottom line for all athletes is to ditch the old school habit of eating egg whites only and start eating the WHOLE EGG. The yolk is where it's at.