Egg Nutrition: Yolk vs. White
Egg yolks are indeed full of cholesterol. Like most cholesterol-rich foods, they are jam-packed full of important nutrients, especially the fat-soluble vitamins and essential fatty acids.
In fact, the slew of nutrients in an egg yolk is so comprehensive that a few a day would offer better insurance than a multi-vitamin. Most importantly, the yolk contains most of the nutrients in an egg.
Egg whites, on the other hand, contain far fewer nutrients. The only thing that could justify their consumption is their attachment to their companion yolk.
Don't believe it? Below is a table that compares the nutritional value of egg whites and yolks, with data provided by the USDA. I've included additional analysis in the last two columns that provides the percentage of the total nutrition found in the yolk and the percentage of total nutrition found in the white.
the yolk contains 100% of the carotenoids, essential fatty acids, vitamins A, E, D, and K (6 items). The white does not contain 100% of any nutrient.
The yolk contains more than 90% of the calcium, iron, phosphorus, zinc, thiamin, B6, folate, and B12, and 89% of the panthothenic acid (9 items). The white does not contain more than 90% of any nutrient, but contains over 80% of the magnesium, sodium, and niacin (3 items).
The yolk contains between 50% and 80% of the copper, manganese, and selenium, while the white contains between 50% and 80% of the potassium, riboflavin, and protein.
It should also be kept in mind that the yolk of an egg is smaller than the white. Where the white contains a slim majority of nutrients, such as protein, this is not due to a greater concentration in the white, but simply to the fact that there is more white in the egg than yolk.
One important set of nutrients that should not be overlooked is the long-chain essential fatty acids. Egg yolks contain the long-chain omega-3 fatty acid DHA, which is necessary for the brain and proper retinal function in the eye, and the long-chain omega-6 fatty acid arachidonic acid, which is required for the healthy skin, hair, libido, reproduction, growth and response to injury. These fatty acids are primarily needed by young children, pregnant and lactating women, and people with degenerative diseases involving oxidative stress, especially those of the nervous system such as Alzheimer's. While fatty fish and cod liver oil supply DHA in larger amounts, egg yolks have an advantage over these foods because they also contain arachidonic acid and because they do not contain EPA, which interferes with arachidonic acid metabolism.
According to NutritionData.Com, one egg yolk contains 75 mg of arachidonic acid (AA), 20 mg of DHA, but no EPA. As I describe in my Special Report, How Essential Are the Essential Fatty Acids?, DHA and AA are the two fatty acids essential to humans and other mammals, while EPA interferes with the body's use of AA and probably does not belong in the mammalian body at all.
Animal foods from animals raised on pasture are likely much richer in DHA. In all eggs, both the DHA and AA are contained in the yolk.
Concerned about the cholesterol in egg yolks? Worried about protecting your heart health? Egg yolks have long been maligned because of their cholesterol content, but cholesterol itself does not cause heart disease. In fact, while LDL, a major carrier of cholesterol in the blood, does have a role in heart disease, it is when poor metablism, deficient diets, and toxins destroy the LDL particle that heart disease develops
And, in fact, the University of Connecticut has extensively studied the effects of eggs on cholesterol levels. These high-quality controlled studies have shown that when people consume three to four eggs per day, with the yolk, virtually everyone experiences either no change or beneficial changes in their cholesterol levels.
