The Incredible, Edible Egg Yolk
July, 2005
Egg yolks? But they're full of cholesterol!
I'm sure you've heard it before. When you think of a "health freak," you don't think of someone eating egg yolks and discarding the white.
Think again.
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.
Table 1: Egg Yolks Versus Egg Whites
Data taken from the USDA Nutrient Database for Standard Reference, Release 15. AA and DHA data from NutritionData.Com. Since the article was written, the USDA has published revisions. The latest, Release 17, can be found here.
As you can see from the table, 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.
Egg Yolks Would Resolve Americans' Most Common Nutrient Deficiencies
According to the Executive Summary of the Third Report on Nutrition Monitoring in the United States by the Interagency Board for Nutrition Monitoring and Related Research of the Federation of American Societies for Experimental Biology's Life Sciences Research Office, the following is true:
Most groups have a deficient median intake of magnesium.
Several groups have a deficient median intake of calcium.
Children aged 1-2 and most groups of females have a deficient median intake of iron.
Blacks over the age of 16 and Mexican-Americans over the age of 60 have a deficient median intake of folate.
All age groups and races have a deficient median intake of vitamins A, E, B6, and copper.
Considering this information, the importance of the egg yolk and relative unimportance of the egg white becomes even more clear. The yolk contains the majority of the copper, nearly all of the calcium, iron, folate, and B6, and 100% of the vitamins A and E.
The white, on the other hand, is only useful as an added source of magnesium, or if the diet is on the whole deficient in protein. The simple addition of an adequate amount of meat in the diet would provide for both.
Finally, eggs are an excellent source of carotenoids. These are primarily highly absorbable forms of lutein and its partner zeaxanthin. These carotenoids accumulate in the back of the eye and appear to protect against age-related macular degeneration. There is no RDA for them, as researchers are still trying to understand their importance. All of the lutein and zeaxanthin in an egg is contained in the yolk.
Egg Yolks Contain Essential Fatty Acids DHA and Arachidonic Acid
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.
To Cook, or Not to Cook? The Benefits of Raw Egg Yolks
Many people believe that the health benefits of egg yolks are greater when the yolks are consumed raw. Heat destroys enzymes, reduces the amounts of certain nutrients, and may make the amino acid cysteine less available, which is needed to synthesize the master antioxidant of the cell, glutathione.
Those who eat raw egg yolks report easier digestion, increased stamina, and resistance to illness — not to mention a quicker snack if they're on-the-go.
That said, there is little evidence beyond such anecdotes that egg yolks are truly more beneficial when consumed raw.
There is also little evidence to support the common belief that consuming raw egg yolks is dangerous. Please see Dr. Mercola's article on the safety of eating raw egg yolks if you are concerned about this.
Raw Egg Whites Contain Digestive Enzyme Inhibitors and Anti-Nutrients
Raw egg whites should not be consumed. They contain inhibitors of the digestive enzyme trypsin, which are destroyed by heat. Consuming 100 grams of raw egg white with one egg yolk compared to consuming the same food cooked was shown in one study to reduce protein digestion from 90 percent down to 50 percent.
Raw egg whites also contain an anti-nutrient called avidin. Avidin is a glycoprotein that binds to the B vitamin biotin, preventing its absorption. Biotin is necessary for fatty acid synthesis and the maintenance of blood sugar, and is especially important during pregnancy when biotin status declines.
Residual Egg White Avidin — Cooking Does Not Fully Destroy the Anti-Nutrients
It is a myth that light cooking completely destroys the avidin.
According to this study, poaching eggs only destroys one third of the avidin while even frying leaves 30 percent of it behind.
This raises the question of whether there is a net nutritional advantage to eating any egg whites at all. Most likely, it depends on the individual person. There is controversy over whether biotin produced in the intestinal tract is absorbed — if intenstinal biotin production is indeed nutritionally important, then people whose intestinal flora are less avid producers of biotin probably need to be more concerned about the potential adverse effects of consuming egg white.
Finding The Right Kind of Eggs
Pastured eggs, meaning eggs from chickens that are free to forage for grass and insects, are of much higher nutritional quality than eggs from confinement chickens. The marginal increase in value, of course, is found mostly in the yolk.
Insects provide a higher DHA content, found exclusive in the yolk, and grass provides a higher vitamin E and carotene content, also found exclusively in the yolk. Egg yolks from pastured chickens are thus a powerful supplement to a healthy diet — a super-food — providing necessary nutrients in which the Standard American Diet is deficient.
To find a source of eggs from chickens raised on pasture, you can visit LocalHarvest.org and do a search for "eggs pastured" or "eggs grass fed" with your zip code. You can also visit EatWild.com and click on your state for a list of farms that pasture their animals.
Additionally, you may be able to find roadside stands in your area that sell eggs from pastured chickens. Be sure to inquire about the farming practices, to make sure that the chickens are able to forage for both grass and insects.
Back to the Basics: Taste!
The truth is that most satisfying meals one could make with eggs just don't taste right without both the yolk and the white. Most baked goods come out with a richer taste and a better texture when the yolks are included. Food should provide good nutrition — for which inclusion of the yolks is necessary! — but it should also taste good.
Food should be fun. It should be rewarding to cook, delicious to eat, and relaxing to indulge in.
The anti-cholesterol establishment upholds its poor theory and unjustified conclusions only to condemn us to a bland and unsatisfying diet, the cornerstone of which is "light cooking" with bland and taste-challenged "foods" like the notorious, emasculated, yolkless egg white.
Fear not.
You are now armed with the raw facts from the USDA's nutrition database that shows that missing out on the egg yolks means missing out on the nutrition in your breakfast. Take heart in this the next time you enjoy the incredible, edible egg yolk.