Friday, February 10, 2012

The Myth of Cholesterol and Heart Disease

We’ve all seen the advertisements about cholesterol. One day, eggs are good for you, the next, they’re filled with evil cholesterol, then they’re good for you again. Drug manufacturers sell pills by the billions to people looking to lower their cholesterol and, hopefully, avoid heart disease. Many doctors blindly repeat to patients, many of whom are at risk of heart disease, to avoid eating cholesterol-rich foods.

While we briefly addressed the issue of cholesterol in our post about a healthy diet, this particular issue is the cause of so much confusion by patients and physicians alike that it really deserves a more detailed discussion. Decades worth of misinformation and improperly interpreted research studies (much of which, when reexamined, do not appear to be correct) have muddled the issue. Furthermore, there is no shortage of people who firmly believe that cholesterol is something to be strictly avoided. But, does avoiding cholesterol actually help to reduce the incidence of atherosclerosis and heart disease?

WHERE DID THE CHOLESTEROL MYTH COME FROM

The Cholesterol Myth: “Cholesterol is bad for you and causes heart disease, so you should try to lower your cholesterol.”

It seems obvious that eating cholesterol rich foods will raise cholesterol levels, doesn’t it? While it may be intuitive, this is essentially incorrect. In fact the dietary intake of cholesterol is essentially meaningless in those suffering from “elevated cholesterol” levels. This myth was put forth by an early research study done by a doctor named Ancel Keys back in 1953. This study is incredibly misleading and has been the cause of an enormous amount of confusion and poor public policy decisions concerning cholesterol and fat intake ever since. So let’s have a look at the history of how this myth developed and was perpetuated in order to better help us explain the facts about what actually matters maintaining heart health.

FLAWED RESEARCH by ANSEL KEYS

Ancel Keys was one of the biggest proponents of the theory that dietary cholesterol and fat had a negative affect on cholesterol levels in the body. While his goal was to try to understand the cause of and eliminate heart disease, which is noble, he ended up creating and spreading one of the most persistent myths about both diet and heart disease. His hypothesis was that dietary fat caused higher levels of cholesterol in the blood. Unfortunately, he wanted to believe his hypothesis so badly that he fell into the trap of ignoring data that simply didn’t fit. Despite the discrepancies in the data from his hypothesis, he decided to select only certain data that showed a very strong link.

Dr. Keys released a convincing diagram in 1953 which showed a very neat correlation between the levels of dietary fat in six countries and the rates of coronary heart disease in those countries. It was part of a very famous document called “The Seven Countries Study”, which has since been roundly refuted and shown to be poorly done science. This diagram appeared to show what can only be described as a perfect match between the level of calories from dietary fat and rates of coronary heart disease, making his theory appear to be perfectly correct. To this day, the concept of a low-fat diet is preached by many as essential to preventing heart disease.


Ignoring, for a moment, a well established mantra of science (“correlation does not imply causation”), there are a number of fundamental flaws with the data that Ancel Keys presented.

The left diagram is from the original Keys study. The right
contains the country data omitted by Keys.

While the data points he used were technically correct, he only used data from 7 countries when, at the time, data was available for 22 countries. If those other 16 countries are added into the diagram, the neat line matching fat intake to coronary heart disease loses virtually all meaning. In fact, when we look at countries that had very similar levels of dietary fat intake (for example, Mexico and Finland) the actual rates of coronary heart disease in these countries differs markedly (by up to seven times). As you can see from the following diagrams, which select at random data from 4-6 other countries from the 22 total, the graph can easily be swayed to show whatever you want to believe, on either side of the argument.




As you can see, the results can be drastically different, depending on the country data you choose. If the hypothesis were correct, these lines should all be roughly the same, no matter what countries are chosen.

The second problem with the study, and how it was used to change public policy, is that the data points were obtained from only men. Since this chart was used to influence dietary recommendations for everyone (e.g., the “food pyramid”), it may not be correct to make a blanket statement about all humans, men and women alike.

Another big problem with the Keys diagram is that the data used as “Calories from Fat” isn’t, as you might expect, the amount of fat actually consumed in a meal, but rather the amount of fat “available for consumption” during that meal. This figure doesn’t account for the fat that comes out of food during cooking, the bits of gristle and fat left on a plate after a meal or even the amount of fat trimmed off of meat before it is even sold in the first place. Clearly his calculation for “Calories from Fat” cannot be considered an accurate representation of how many calories people in different countries actually get from fat.

Interestingly enough, if you plot the number of new TVs and radios sold in some of these 22 countries, you also find a pretty closely matching plot to the amount of coronary heart disease in that country. While corresponding research into lower exercise levels and heart disease help strengthen the association, you can’t simply state that buying televisions and radios “causes” coronary heart disease. Rather there may be an association between television and radio sales and a sedentary lifestyle, but that cannot be taken to mean that somehow you will get coronary heart disease from simply buying a radio!

Keys also only bothered to look at levels of dietary fat, the focus of his hypothesis. He didn’t even bother to seriously consider what effect higher levels of sugar had on the numbers. To prove his hypothesis, he would have had to show that keeping levels of sugar constant and increasing only fat would actually increase heart disease. Keys himself even admitted that sugar intake correlates very well with heart disease. Here is an excerpt, from page 262 of his own work.
“The fact that the incidence rate of coronary heart disease was significantly correlated with the average percentage of calories from sucrose in the diet is explained by the intercorrelation of sucrose with saturated fat.”
So, in other words, he said that this is because in foods rich in saturated fat there is also sugar, and simply dismissed the effect of sugar. Well, this fat and sugar combination might be true of foods like donuts, but clearly not with meat or vegetables. He decided the conclusion, without even bothering to test whether fat or sugar is the cause of the heart disease.

Cherry picking data that fits a theory is one of the many tell-tale signs of bad science. Since the release of the Keys diagram, there have not been any actual diet studies which support his theory with hard data. In fact, the amount of dietary fat consumed in the United States has been on a steady decline over the last few decades, but coronary heart disease rates are still increasing.

It seems clear now that Ancel Keys was very wrong and that fat intake does not cause or even correlate with an increased incidence of heart disease. In fact, heart disease is probably much more tied to the amount of sugar and carbohydrates a person eats then to perhaps any other factor other than smoking. We will discuss why sugar and carbohydrates are so bad for you heart later in our discussion.

OLDER STUDIES IGNORE CONFOUNDING VARIABLES

After the study done by Ancel Keys, misconceptions about cholesterol, fat, and their association to heart disease continued. Unfortunately, his ideas were perpetuated based on old research studies done many years ago. These older studies did not take into account confounding variables (variables that interfere with the interpretation of a research study). We now know that these confounding variables are incredibly important and skewed the results of almost all of these early studies.

Basically, by not tracking information like the level of sugar/carbohydrates consumption in the diet or even the contributions of exercise, smoking, exposure to environmental toxins, as well a host of other potential confounding variables, this early research is essentially meaningless. It seems obvious to us now that smoking, exercise, and all these other factors play a huge role in health and the development of heart disease, but in the middle of the 20th century, these issues were not recognized as important.

Because these confounding variables were not understood at the time researchers made no effort to take them into account when they organized their research studies. So the earliest governmental recommendations for a  “healthy” diet were based on hopelessly flawed data. Many of these recommendations are still perpetuated in our popular culture today despite a large body of properly done research that now shows these early studies to be completely wrong and misleading.

SO WHAT CAUSES HEART DISEASE, IF NOT CHOLESTEROL?

We now know that sugar, not fat, is one of the largest contributors to coronary heart disease. Most of this damage comes from what is now called “metabolic syndrome”, a precursor for diabetes. This is a subject we will discuss in more depth in part 2 of this post, but it is important to note couple of key points here.

First and foremostl, “unhealthy” levels of cholesterol in the body are not actually unhealthy, and about half of all heart attacks occur in people who don’t even have elevated levels of cholesterol. This alone is a huge red flag that should point us in another direction for finding out what causes coronary heart disease to occur. Cholesterol is not in and of itself dangerous and, despite its vilification, is absolutely essential to your body.

Second, unfavorable levels of lipoproteins (cholesterol carrying molecules) in the blood are generated by eating a diet high in sugar and carbohydrates. Eating a diet consistently high in carbohydrates and sugar causes changes to body chemistry which lead to “metabolic syndrome”, diabetes, obesity, and then to heart disease.

In our followup to this article, we will discuss what actually causes coronary heart disease, and how to avoid (and even reverse) damage to arteries that can lead to heart attacks. In addition, we will discuss the role of statin drugs in treating high cholesterol


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Researched and written by Dr. Rebecca Malamed, M.D. with assistance from Mr. Malcolm Potter.

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