Saturday, May 31, 2008

Diet Cholesterol and Cardiovascular Disease

High blood cholesterol has been shown to be a leading cause of cardiovascular disease, coronary heart disease and stroke. However cholesterol itself is essential to several important processes within the body, including cell membrane structure and function, making of hormones and the digestion and movement of fats to all parts of the body.

So why does an essential compound result in such big problems?

The answer lies in a more detailed understanding of cholesterol, how it can result in high blood cholesterol and the reasons high blood cholesterol results in blood vessel damage.

Interestingly, the body can make all the cholesterol it needs although typically it makes around 2/3rd and the remaining 1/3rd comes from your diet. Further, not all of your diet sourced cholesterol is absorbed and absorption rates vary widely. A range between 20% and 80% is possible with an average of around 60%. Absorption appears to be regulated so that cholesterol levels remain at a constant level within your body.

It is widely thought that high blood cholesterol is the main risk factor for coronary atherosclerosis. Evidence from several major studies suggests that high blood cholesterol causes coronary heart disease (CHD). It’s estimated that it accounts for around half of the increased risk of CHD in a middle aged man with total blood cholesterol of 6.2 mmol.L-1. As your blood cholesterol increases and your HDL-C (good cholesterol) decreases, so your risk of CHD increases.

This is supported by large studies. The MRFIT study followed 360,000 men for six years. It showed that the risk began at levels as low as 4.65 mmol.L-1 and the risk was large. The risk of CHD for the highest 10% is four times that of the lowest 10%.

It is now thought that LDL-C (low density lipoprotein cholesterol) is the most damaging and rather than total cholesterol the better predictor of CHD is the total blood cholesterol to HDL-C (high density lipoprotein cholesterol) ratio.

Contrary to what may seem obvious the level of cholesterol in your diet doesn’t show a significant independent correlation to your risk of CHD. Although it had been shown to be the case in animal studies an analysis of the Framington Heart Study indicated that dietary cholesterol was not a predictor of total blood cholesterol or of LDL-C levels in women.

The problem food in your diet is saturated fatty acids (SFAs). The Seven Countries Studies of over 11,000 middle aged men in 7 countries indicated a strong independent correlation between eating SFAs and CHD.

It’s been found that SFAs in your diet raise total blood cholesterol approximately twice as much as polyunsaturated fatty acids (PUFAs) lowered it. Monounsaturated fatty acids (MUFAs) were found to be neutral and dietary cholesterol, like that in egg yolks, has only a comparatively small effect. It is thought that the body adapts to a high cholesterol diet in several ways:
  • Reduction of intestinal absorption
  • An increase in conversion to bile acids
  • Reduction in the amount made in the body
  • Changes in LDL-C receptor activity
While the general effect is small some individual’s response is more extreme. Half of this variation is put down to genetic factors.

How Does High Blood Cholesterol Result in Blood Vessel Damage?

Cholesterol can build up on the walls of your arteries. This build up of cholesterol is called plaque and over time it can cause narrowing of the arteries. This is called atherosclerosis or hardening of the arteries. The arteries that bring oxygenated blood to supply the heart are called coronary arteries.

Narrowing of your coronary arteries due to plaque can slow down the flow of blood to your heart resulting in a decrease in the amount of oxygen-rich blood it receives. If the heart doesn’t receive enough oxygen then angina or chest pains can result. A complete blockage results in a heart attack and possible death.

Lowering your blood cholesterol level decreases your chance for having a heart attack and may also slow down, reduce, or even stop plaque from building up.

Saturated Fats You Should Reduce
  • Animal fat especially fatty meat: salami, sausage meat, minced meats, trim the hard white fat from red meats and remove the skin from poultry.
  • Full-fat diary products
Use vegetable oils in cooking instead of animal fat. Good examples include canola and olive oil.

The message is clear. If you want to be healthier then lower your saturated fat intake and exchange it for polyunsaturated fats and monounsaturated fats.

No comments: