Thursday, 31 July 2008

High Cholesterol : Fact or Fiction Pt 3

Cary G Dean.

Dietary Fats and Heart Disease

That diet might play a part as a cause of CHD was hypothesised by another American doctor, Ancel Keys, in 1953.

Using data from seven countries in his 'Seven Countries Study', Keys compared the death rates from CHD and the amounts of fats eaten in those countries to demonstrate that heart disease mortality was higher in the countries that consumed more fat than it was in those countries that consumed less.

(At that time, data from many more countries were available. It seems that Keys ignored the data from those that did not support his hypothesis.)

And so the 'diet/heart' hypothesis was born.

But how do we know it is true?

It is all very well having a theory, what you have to do then is prove it.

In medicine, the usual way is to select two groups of people, as identical for sex, age, and lifestyle as possible.

One group called the control group , carries on as normal while the other, called the intervention group , tries the new diet, drug or whatever.

After a suitable time, the two groups are compared and differences noted.

Keys' fat-diet/heart disease hypothesis was persuasive so, to test it, several large-scale, long-term, human intervention studies were set up in many parts of the world.

These involved hundreds of thousands of subjects and hundreds of doctors and scientists and cost billions of dollars in an attempt to prove that a fatty diet caused heart disease.

Framingham Heart Study

The most influential and respected investigation of the causes of heart disease is the Framingham Heart Study.

This study was set up in the town of Framingham, Massachusetts, by Harvard University Medical School in 1948 and is still going on today.

It was this study that gave rise to the dietary 'risk factors' with which we all are so familiar today.

The Framingham researchers thought that they knew exactly why some people had more cholesterol than others - they ate more in their diet.

To prove the link, they measured cholesterol intake and compared it with blood cholesterol.

Although subjects consumed cholesterol over a wide range, there was little or no difference in the levels of cholesterol in their blood and, thus, no relationship between the amount of cholesterol eaten and levels of blood cholesterol was found.

(Although it is interesting that women who had the highest levels of cholesterol in their blood were ones who had eaten the least cholesterol.)

Next, the scientists studied intakes of saturated fats but again they could find no relation.

There was still no relation when they studied total calorie intake.

They then considered the possibility that something was masking the effects of diet, but no other factor made the slightest difference.

After twenty-two years of research, the researchers concluded:

"There is, in short, no suggestion of any relation between diet and the subsequent development of CHD in the study group."

On Christmas Eve, 1997, after a further twenty-seven years, the Journal of the American Medical Association (JAMA) carried a follow-up report that showed that dietary saturated fat reduced strokes.

As these tend to affect older men than CHD, they wondered if a fatty diet was causing those in the trial to die of CHD before they had a stroke.

But the researchers discount this, saying:

"This hypothesis, however, depends on the presence of a strong direct association of fat intake with coronary heart disease.

Since we found no such association, competing mortality from coronary heart disease is very unlikely to explain our results."

In other words, after forty-nine years of research, they are still saying that they can find no relation between a fatty diet and heart disease.

Multiple Risk Factor Intervention Trial

One of the largest and most demanding medical studies ever performed on humans, The Multiple Risk Factor Intervention Trial (known in the medical world, by its initials, as MR. FIT) involved 28 medical centres and 250 researchers and cost $115,000,000.

The researchers screened 361,662 men and deliberately chose subjects who were at very high risk to ensure that they achieved a statistically significant result.

They cut cholesterol consumption by forty-two percent, saturated fat consumption by twenty-eight percent and total calories by twenty-one percent.

Yet even then they didn't succeed.

Blood cholesterol levels did fall, but by only a modest amount and, more importantly, coronary heart disease was unaffected.

Its originators refer to the results as "disappointing" and say in their conclusions:

"The overall results do not show a beneficial effect on Coronary Heart Disease or total mortality from this multifactor intervention."

The Tecumseh Study

The Tecumseh Study attempted to correlate blood cholesterol levels measured one day with the amounts of fats eaten the previous day - but found none.

Interestingly, the people who ate the least cholesterol had the highest levels of blood cholesterol.?

Although not looking for it, this study also found that blood cholesterol levels were quite independent of whether the dietary fats were saturated or unsaturated.

Thus another 'diet-heart' hypothesis, that only saturated fats are to blame, was invalidated.

For what a man would like to be true, that he more readily believes.
Francis Bacon

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