Friday, February 24, 2012

How Standard Dietary Advice To Avoid Cholesterol-Rich Foods Is Misguided

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How Standard Dietary Advice To Avoid Cholesterol-Rich Foods Is Misguided Dr. John Briffa

Recently, a lady sent me some blood test results that she'd scanned into her computer. The test results showed 'elevated' LDL-cholesterol levels. Accompanying the test results was a diet sheet from her doctor, telling her to avoid cholesterol-rich foods such as eggs and shellfish. The idea that people with 'raised' cholesterol should avoid eating cholesterol-rich foods has been around for decades. The question is, is there any evidence to support this advice?

Firstly, does eating cholesterol-rich foods cause cholesterol levels to go up? The evidence is a little mixed in this area but, on balance, the answer to this question appears to be 'no'. For example, there are studies which show that adding significant quantities of eggs to the diet has no impact on total blood cholesterol levels.

One reason for this is that the majority of cholesterol in the bloodstream does not come directly from the food we eat, but is manufactured in the liver. There is a thought that when individuals eat more cholesterol their liver makes a little less to compensate. On the other hand, eating less cholesterol is likely to have an impact on blood cholesterol levels as, in this case, the liver will make more in return. It seems the body is keen to maintain cholesterol levels.

But as I've pointed out repeatedly on this blog, the impact cholesterol (or anything else) has on blood cholesterol levels is irrelevant - it's its impact on health that is important. Some of the evidence we have in this area is what we call 'epidemiological' in nature. Such studies look at associations between things. Relevant studies do not link dietary cholesterol intake with heart disease risk in populations. In other words, individuals who eat more cholesterol do not, generally speaking, appear to be at an increased risk of heart disease. The fact that no association between cholesterol intake and heart disease exists makes it very unlikely that dietary cholesterol is a significant cause of heart disease.

Some of the evidence on cholesterol comes from studies in which individuals are fed cholesterol to see what this does to them on a biochemical level. A minority of people will see an increase in their cholesterol levels and are sometimes termed 'hyper-responders'. However, as a review on the subject pointed out, any rise in blood cholesterol level is due, at least in part, to an increase in supposedly protective 'HDL-cholesterol' [1]. Plus, these studies also tend to find that feeding cholesterol to people reduces the levels of potentially harmful 'small dense' LDL-cholesterol, which I wrote about recently here.

Put all of this together and it seems that the commonly-given advice for individuals to avoid cholesterol-rich foods is misguided. It also runs the risk of individuals missing out of foods, such as eggs, which have many nutritional attributes.

Here's to a healthy heart.

References:

1. Fernandex ML, et al. Revisiting dietary cholesterol recommendations: does the evidence support a limit of 300 mg/d? Curr Atheroscler Rep 2010;12(6):377-83.

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