Cholesterol - The dangers of low-fat diets

For a lot of people it is not clear whether high cholesterol levels are a risk factor of coronary heart disease. The conventional wisdom tells you to cut fat from your diet in order to reduce total cholesterol level or the bad cholesterol level (LDL). So doctors advise to lower your fat intake. This is a bit simplistic.

First of all, triglycerides and VLDL levels are a much better predictor of coronary heart disease. Total cholesterol level says nothing about your risk of heart disease. Second, triglycerides and VLDL are elevated on a high carbohydrate diet.


1. A bit of science first:

Fatlike substances circulating in our bloodstream:
- Cholesterol
- Fatty acids
- Triglycerides: composed of 3 fatty acids linked together by a glycerol molecule.

These are packaged in these different size balloons, called lipoproteins, and transported in the bloodstream to various areas of our body.

These balloons (lipoproteins) are called:
- VLDL: very low density lipoproteins (big and fluffy)
- IDL: intermediate density lipoproteins
- LDL: low density lipoproteins (smaller)
- HDL: high density lipoproteins

You can find inside the balloons (lipoproteins):
- cholesterol
- triglycerides (fat)

The risk of coronary heart disease is predicted by these factors:
- high VLDL count
- high triglycerides

Elevated triglyceride levels in the blood are far more common in coronary heart disease patients than high cholesterol.

VLDL contains most of the triglycerides and some cholesterol. So, if we have an elevated number of VLDL particles, we also have high triglyceride levels.

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2. The effect of diet:


Here is Pete Ahrens (Rockefeller University, 1955) findings on fat in the blood:

"When he gave lectures, Ahrens, would show photos of two test tubes of blood serum obtained from the same patient - one when the patient was eating a high carbohydrate diet and one on a high fat diet. One test tube would be milky white indicating lipemia [= an excessive concentration of fat in the blood]. The other would be absolutely clear. The surprising thing, Ahrens would explain, was 'that the lipemic plasma was obtained during the high-carbohydrate period, and the clear plasma during the high-fat regimen.'"
                                                                                       - Gary Taubes

This means that the ratio of fat in the blood raises on a high-carbohydrate diet and drops on a high-fat diet. 

A bit more detailed explanation:
- When we eat carbohydrates, the bloodstream is flooded with glucose (sugar).
- The liver takes some of this glucose and transforms it into fat (triglycerides) for storage. The more carbohydrates or sugar we consume, the more fat (triglycerides) is produced in the liver. 
- These triglycerides are packaged in big balloons known as VLDL.
- These VLDL balloons will be secreted by the liver back into the bloodstream.
- The VLDL on its way, will release it's fat (triglyceride) content wherever it's needed, and will end his life as an LDL particle.
- This means the more VLDL our liver secretes, the more LDL particles in our blood. 
- These LDL particles are small in size, which is bad for our heart disease profile.

(Here, I oversimplified the science. The size of the LDL particles matters as well! VLDL ends up in a small size LDL particle. If the small LDL particle count is elevated, it is a risk factor for heart disease. This is exactly what is happening on a high-carbohydrate diet.)

More carbohydrates - more glucose - more triglycerides - more small LDL - elevated risk of heart disease

Only by restricting carbohydrates in our diet, can VLDL be lowered. On a low-fat, carbohydrate-rich diet, VLDL rises disproportionately. So prescribing a low-fat, high carbohydrate diet to a patient who already has a high VLDL, is increasing his risk of heart disease even further. 

Number of triglycerides are high on a low-fat diet and are low on a high-fat diet. On a high-fat diet, trigycerides are hard to come by, and the number of VLDL secreted by the liver is considerably lower, which is a good sign for us.

So, eat your fat, rather than carbohydrates.