Eggs have been part of the human diet since the chicken was first domesticated in Asia over 4000 years ago. Many people believe that eggs are detrimental to the health because they are energy (calorie), saturated fat and cholesterol dense. This is based on the tired old fallacies that saturated fat and cholesterol are the cause of cardiovascular disease, and that high energy foods make you fat. Many nutritional studies have been performed on eggs and egg eaters and when these are viewed in their entirety the evidence for eggs being linked to either weight gain or cardiovascular disease is really non-existent. A shame therefore that many people avoid eggs, because eggs are actually a very good source of nutrients, many of which have been shown to be cardioprotective. Nutritionally eggs contain all the nutrients to create and grow a live chick. Eggs are therefore a good source of essential nutrients including many of the essential nutrients required for human growth and development.
The cardioprotective effects of eggs are evidenced by the nutrients they contain. Betaine is one such nutrient that is known to possess cardioprotective effects. Betaine is able to reduce plasma levels of homocysteine, an amino acid derived chemical that is known to induce oxidative stress in humans. The homocysteine induced oxidative stress is now thought to be a primary driver of the endothelial dysfunction that may be required for the development of cardiovascular disease. Betaine reduces homocysteine levels because it allows conversion of homocysteine to the amino acid methionine, thus reducing tissue levels of the former. Eggs are also a good source of B vitamins, and three of the B vitamins, folic acid, vitamin B12 and vitamin B6 are also able to reduce plasma levels of homocysteine. In this regard, vitamin B12 and folic acid are required as cofactors for the conversion of homocysteine to methionine, and vitamin B6 is required as a cofactor for the conversion of homocysteine to cysteine.
The B vitamins and betaine are therefore key cardioprotective nutrients that can be derived from eggs. However, this is not where the cardioprotective effects of eggs stops. Free range eggs are also a good source of the omega-3 essential fatty acid alpha linolenic acid (ALA, C18:3 (n-3)). The content of omega-3 fatty acids in eggs is dependent on the diet of the chicken. Those given access to a wide range of natural foods tend to accumulate omega-3 fatty acids such as ALA in their eggs, while those fed a restricted and omega-3 deficient diet are not able to do this. Therefore free range eggs tend to be high in omega-3 fats whereas battery reared chicken eggs are not. Omega-3 fats have been shown to be cardioprotective for a number of reasons. Firstly, they reduce inflammation because they are required for the production of anti-inflammatory signal molecules in cells. Secondly, they are able to reduce platelet aggregation. Thirdly, they can alter fat metabolism in the liver and thus reduce triglyceride levels.
The ability to regulate fat metabolism in the liver is an important mechanism by which omega-3 fatty acids prevent cardiovascular disease. However, eggs contain another substance, choline, that may also be cardioprotective because of its effects on liver fat metabolism. Choline is often grouped with the B vitamins, although it can be synthesised in the body from the amino acids methionine and serine. Choline is a lipotropic agent, that is required for the correct metabolism and export of lipids from the liver. This related to the fact that choline is required for the formation of lipoproteins as it is a key component of the phospholipids that are the building blocks of the very low density lipoproteins (VLDL) that export fatty acids from the liver. Choline also plays a role in homocysteine metabolism because it can be converted to betaine, which as mentioned above is a cardioprotective nutrient. Choline is so important to human nutrition that it is now regarded as an essential nutrient, and eggs are one of the best sources.