The cholesterol theory of cardiovascular disease states that increases in dietary cholesterol are the cause of increases in plasma cholesterol. In turn, this rise in plasma cholesterol is the cause of atherosclerosis, and this atherosclerosis is the cause of cardiovascular disease. This cholesterol theory of cardiovascular disease is based on scientific evidence from almost 70 years ago. Further, much of this evidence has since been questioned for its validity. For example, one particular study, the Seven Countries study by Ancel Keys and his coworkers, has been shown to be based on unscientific methodology because it contains author selection bias. More recent studies have also improved understanding of the physiology of cardiovascular disease in terms of the role of endothelial dysfunction. Factors such as oxidative stress, insulin resistance and plasma homocysteine concentrations, that were previously not even considered by researchers, have now been shown to be pivotal in the development of cardiovascular disease.
It is surprising that proponents of the cholesterol theory cling onto the notion that dietary cholesterol is problematic because evidence has never really supported the theory. If an example of spin, misdirection and outright lies in science is ever sought, the cholesterol theory of cardiovascular disease comes about as close as any other pertinent examples. Many people avoid cholesterol containing foods under the erroneous belief they are benefiting their health. In fact such individuals, by focussing on the wrong target, are doing their health a disservice. Eggs are a classic example of a healthy food that has been vilified by the medical establishment for no scientific reason, causing many people to avoid a food that might actually benefit their health. That eggs do not cause detrimental changes in the plasma cholesterol levels of healthy free living people has been reported (here). Further, metabolic studies that rigorously control macronutrient intakes have also not shown eggs to lead to detrimental changes in plasma lipoprotein levels.
For example, in one study1, researchers fed male subjects a diet containing either 400 mg of cholesterol or 1400 mg cholesterol in order to investigate the effects of dietary cholesterol on plasma cholesterol and lipid levels. The diets were identical in their protein, fat, carbohydrate and polyunsaturated to saturated fatty acid ratios. The extra 1000 mg of cholesterol in the high cholesterol group was supplied by the addition of four eggs. Following four weeks, there were no significant differences between the total plasma cholesterol, high density lipoprotein (HDL), low density lipoprotein (LDL) or triglyceride levels between the groups. Therefore adding eggs to the diet was not able to alter mean plasma cholesterol or triglycerides. In individual analysis of the subjects, the authors reported that seven of the twelve subjects had no changes in plasma lipids, while five showed increases. However, of these five, two showed baseline levels of plasma lipids by the study end, showing that eggs affected negatively only three of the twelve subjects.
Evidence to date suggests that eggs are cardioprotective. Eggs are good sources of essential nutrients including B vitamins, low intakes of which are a risk factor for cardiovascular disease. In addition eggs contain high concentrations of lecithin, a lipid substance containing high concentrations of phospholipids such as phosphatidylcholine, phosphatidylethanolamine and phosphatidylinositol. Dietary lecithin is able to influence the metabolism of fatty acids in the liver because of its phosphatidylcholine content. Studies show that supplements of phosphatidylcholine are able to reduce fatty acid accumulation in the liver. In fact the efficacy of phosphatidylcholine to reduce fatty acids from the liver has lead many to suggest that such accumulation of fats within the liver is a phosphatidylcholine deficiency. Because non-alcoholic fatty liver is associated with detrimental metabolic changes that increase the risk of cardiovascular disease, eggs may confer protection despite their high cholesterol content.
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