06 December 2013

About Cholesterol

I received a lot of requests recently about high cholesterol levels and their implication in heart disease. I made a few graphs to make it easy to understand.

There are different types of lipoproteins (kind of bags) carrying different types of lipids (fats) and other things:

  • VLDL (Very-Low-Density Lipoprotein): it’s core is mainly triglycerides (green).
  • IDL (Intermediate-Density Lipoprotein): it carries less triglycerides than the VLDL.
  • LDL (Low-Density Lipoprotein): it has less triglycerides (green) and more cholesterol. It is usually called the “bad” cholesterol. The LDL varies in size, the smaller the more dangerous.
  • HDL (High-Density Lipoprotein): it is only about 5% triglycerides. HDL is called the “good” cholesterol.

Dr Ronald Krauss (University of California, Berkeley) investigated the relationship between LDL levels and heart disease. He found that there was no direct correlation between these two data. There were people with high LDL, but still not developing heart disease, and the opposite was also true, some people had heart disease without having a very high LDL. 

Krauss grouped LDLs in different classes according to their size. He realized that those who had a high risk of developing heart disease, had high levels of small LDL. Those with a low risk of heart disease had large, fluffy LDL. So, someone's LDL level does not say much about this person's heart disease risk. 
Krauss also pointed out that high level of small LDL is "invariably accompanied by high triglycerides and low HDL" (Gary Taubes - Good Calories, Bad Calories).

What really happens is that when we consume a diet high in sugar and refined carbohydrates, it prompts the liver to produce high amounts of triglycerides, which in turn will be packaged in big VLDLs. These VLDLs will circulate in the bloodstream. The triglycerides will be distributed wherever they will be needed (also to the fat tissues). These VLDLs will end their lives as a small size LDLs, which oxidize very easily.

On the other hand, when our diet is devoid of sugar and refined carbohydrates, there are less triglycerides to be packaged. So the liver will produce IDLs (smaller than VLDL and with less triglycerides). These IDLs will end their lives as big size LDLs.

The small LDL oxidizes very easily and will be taken up by certain white blood cells. These small LDLs then release their cholesterol content on the sites of injury of the blood vessels. They are needed to patch up the cracks in these vessels. Over the years or decades, cholesterol accumulates and thickens the artery wall. This condition is called atherosclerosis. Big fluffy LDL's do not oxidize easily and do not accumulate on artery walls.

In conclusion:
  • A diet high in sugar is the cause of the build-up of plaque in our vessels. Dietary fat will not go from stomach to artery lining! Therefore, it is a mistaken belief that by not eating eggs (high in dietary cholesterol), we will avoid heart disease.
  • LDL or total cholesterol does not assess the risk for heart disease. A much better biomarker for heart disease is high triglycerides and low HDL levels, according the Krauss' research.

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