The myth goes something like this: arteries are like pipes; cholesterol is gooey, sticky gunk. When you eat cholesterol, it winds up in your blood. If the cholesterol level in your blood gets too high, it starts caking up the pipes. Thus, if you don't want your pipes clogged, don't eat foods rich in cholesterol.
Such is the basic logic behind advice to avoid eating nutrient-dense foods like liver and egg yolks.
Eating Cholesterol Does Not Raise Blood Cholesterol Levels
The truth is, however, that there is no direct connection between the amount of cholesterol you eat and the concentration of cholesterol in your blood. In most people, eating cholesterol has little or no effect on this amount. In about 30 percent of the population, eating cholesterol does in fact increase the concentration of cholesterol in the blood — but it increases the "good" cholesterol.
To put it in more scientific terms, eating cholesterol "results in a less atherogenic lipoprotein profile."
Egg-Feeding Intervention Trials
In a recent review,1 cholesterol researcher Dr. Maria Luz Fernandez of the University of Connecticut's Department of Nutritional Sciences summarized the results of a number of studies testing the effects of egg consumption on blood cholesterol levels. In children aged 10-12, in men aged 20-50, in premenopausal and postmenopausal women, in whites and hispanics, the same basic finding persists: two or three eggs per day has little or no effect on the blood cholesterol levels of over two thirds of the population.
Less than a third of the population, by contrast, are termed "hyperresponders." When these people eat egg yolks, their cholesterol levels do go up. LDL, the so-called "bad cholesterol," and HDL, the so-called "good cholesterol" both go up equally, so there is no change in the ratio of LDL to HDL, or of LDL to total cholesterol, both of which are considered better measures of the risk of heart disease than the total concentration of cholesterol.
LDL Particle Size — Pattern A vs. Pattern B
Moreover, the actual number of LDL particles do not change at all; they just get bigger. When your doctor measures your blood cholesterol level, the lab reports it by weight. In America, this is usually in milligrams per deciliter. When your "cholesterol level" is high, this means that in a given measure of blood volume (such as a deciliter or a tenth of a liter) the total number of cholesterol-carrying lipoprotein particles weigh more. This could mean that you have more particles, or it could mean that the particles weigh more because they are carrying more cholesterol.
According to research that Dr. Fernandez cites in her review, it is the small, dense LDL particles that raise the risk of atherosclerosis, while the large, buoyant LDL particles are safe. This may be because small, dense LDL particles are much more vulnerable to oxidation. People whose LDL is primarily small and dense have three times the risk of heart disease as people whose LDL is primarily large and buoyant.
In the egg-feeding studies, egg consumption makes the LDL particles of the "hyperresponders" get bigger, not more numerous. When they get bigger, they become less subject to oxidation and accumulation in atherosclerotic plaque.
Busting the Myth
In over two thirds of the population, then, egg consumption leads to little or no change in cholesterol at all. In less than a third of the population, total cholesterol goes up, but both the ratio of LDL to HDL and the total number of LDL particles remains the same; the LDL particles just get bigger and safer.
If arteries were like pipes and cholesterol was like gunk, more gunk would just clog up the pipe — but arteries are nothing like pipes and cholesterol is nothing like gunk. Consider the myth busted.
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Read more about the author, Chris Masterjohn, PhD, here.
1. Fernandez ML. Dietary cholesterol provided by eggs and plasma lipoproteins in healthy populations. Curr Opin Clin Nutr Metab Care. 2006;9:8-12.