Components of the Yolk
The yolk of eggs contain approximately 50% oleic acid, an omega-9 monounsaturated fat commonly found in olive oil. The remaining fat content consists of saturated fats along with a small amount of polyunsaturated fats (PUFAs). The ratio of different PUFAs tends to depend how the chickens were raised. Since the majority of commercially-raised chickens are fed grains high in omega-6 fatty acids, the typical ‘garden-variety’ eggs found your local supermarket will tend to be high in omega-6 fatty acids relative to the omega-3 variety. On the other hand, chickens that are pasture-fed or fed with a special omega-3 enriched diet will tend to have a more balanced ratio of omega-3 to omega-6 fatty acids.
Egg yolks also have high levels of carotenoids (mostly lutein and zeaxanthin) that are capable of increasing carotenoid concentrations in both plasma and specific tissues such as the eyes. Perhaps more importantly, eggs yolks are among the richest sources of Choline, a nutrient associated with a number of health benefits.
Egg yolks contain mostly fatty acids, cholesterol, fat soluble nutrients. Although lower in protein, yolks contain high concentrations of leucine, an essential amino acid.
Protein and the Albumin
The white of the eggs, known as the albumin, contains the majority of the protein within the whole egg and some B-vitamins as well.
The white also contains the protein avidin, which can bind and sequester certain B-vitamins such as biotin, preventing absorption. Luckily, a sizeable portion of avidin is destroyed by prolonged heating or pasteurization, so nutrient loss can be mitigated.
Omega-3 is sometimes added to the diets of hens to increase the omega-3 fatty acid content of the yolks, since the fatty acid composition the yolk tends to depend on the diet of the hen. Omega-3 fatty acids given to hens are usually in the form of ALA (Alpha-linolenic acid), although the omega-3 fatty acids EPA and DHA from Fish Oil are also used. Eggs from hens with EPA/DHA-enriched diets tend to be associated with a ‘fish-like’ taste and scent, which tends to make these eggs less popular.
It should be noted that cholesterol (a steroid molecule) is wholly different from the lipoproteins such as LDL and HDL, which are large molecules containing both fatty acids (lipo-) and amino acids (-proteins) that serve as transportation molecules in the body.
While there may be interaction between dietary cholesterol and serum lipoproteins (since dietary cholesterol is indeed a component of the lipoproteins, among many other things) they are by no means synonymous.
It should also be noted that the body can synthesize its own cholesterol. Cholesterol levels in the blood that are measured during typical blood tests called lipid panels come from two sources: the diet, and that which is manufactured by the body itself. In most people, the amount of cholesterol made by the body is greater than the amount ingested in the diet.
Article provided with permission courtesy of Examine.com