Does a High Cholesterol Diet Really Contribute to Heart Disease?
A high cholesterol diet would be on most people’s list of risk factors when it comes to heart disease, but much of the relevant research does not support this widely held assumption. Many doctors, public health agencies, and public health advocacy groups advise the public to lower the amount of cholesterol in their diet, and Americans have heeded this advice by steadily replacing animal fats, (those high in cholesterol), with processed vegetable oils, (those without cholesterol), over the past century. Death rates from heart disease however have not decreased; in fact they have risen dramatically. We are told by trusted sources that we can reduce our risk for heart disease by consuming less cholesterol, but what is the science behind this advice?
The science linking high cholesterol and heart disease began in the middle nineteenth century with the publication of a study conducted by Rudolph Virchow. His Lipid Hypothesis of Atherosclerosis proposed that heart disease is caused by the deposition of blood lipids in the walls of the arteries. Other studies followed, but most of our modern assumptions about cholesterol and heart disease are based on one study, The Framingham Heart Study. This study begun in 1948 and continuing today is the basis for the widely held view that consumption of cholesterol leads to a greater risk of heart disease. The study concluded in 1961 that high serum cholesterol levels were a significant risk factor in coronary disease. The early results of this study were given a strong public endorsement that same year in a Time Magazine interview with Ancel Keys who earned the nickname Mr. Cholesterol for his many speeches and writings advising Americans to lower their cholesterol intake. The Framingham Study results along with Ancel Keys’s recommendations led the National Institutes of Health, the American Heart Association and others to propose a national campaign to reduce cholesterol consumption.
More recently, and much more dramatically, the fight to reduce dietary cholesterol and presumably heart disease was championed by the advocacy group Center for Science in the Public Interest (CSPI). This group in a famous 1994 study of Italian food restaurants dubbed the classic dish fettuccini Alfredo, A heart attack on a plate. The quote which was often repeated on television and in print was a useful tool to those advocating low cholesterol diets. The CSPI’s assertion is supported by the public information distributed by the American Heart Association and the National Institutes of Health. The effects of a high cholesterol diet are dramatized in this image from the National Institutes of Health website:
Too much cholesterol in the blood, or high blood cholesterol, can be serious. People with high blood cholesterol have a greater chance of getting heart disease. High blood cholesterol on its own does not cause symptoms, so many people are unaware that their cholesterol level is too high.
Cholesterol can build up in the walls of your arteries (blood vessels that carry blood from the heart to other parts of the body). This buildup of cholesterol is called plaque (plak). Over time, plaque can cause narrowing of the arteries. This is called atherosclerosis (ath-er-o-skler-O-sis), or hardening of the arteries.
The image is dramatic, believable, and flawed. Plaque buildup does in fact lead to hardening and constriction of the arteries, but what causes this buildup of plaque? It has been theorized, yet never proven that cholesterol causes the buildup.
Unless it can be proven that cholesterol is responsible for this buildup of plaque, we should not rule out other possible causes. If cholesterol is the culprit, we would expect that replacing cholesterol with other, healthier, fats would lead to a decrease in heart disease. A comparison of animal fat consumption as a proportion of total fat intake with death rates from coronary artery disease over a sixty year period actually showed the opposite to be true. As the proportion of animal fats decreased from 83% to 62% of total fat intake, the death rate actually increased over 3,000%. If it is accepted that a buildup of arterial plaque is a major cause of heart disease, but cholesterol is not accepted as the cause of this plaque buildup, what else should we look at? Newer studies have demonstrated a correlation between elevated homocysteine, (an amino acid) levels and atherosclerosis. Ironically, homocysteine levels can be lowered by consuming more b vitamins and folic acid, nutrients found in the fatty animal foods we have been told to avoid. (5). Researchers have also discovered a correlation between C – reactive protein levels and heart disease. C-reactive proteins are not thought to be a cause, but rather a marker for injury to the arteries that the body is trying to repair. Interestingly, statin drugs have been found to reduce levels of C-reactive proteins in the blood, possibly by reducing the damage and inflammation that the proteins are reacting to. It may turn out that statin drugs are effective in fighting heart disease not by reducing cholesterol, (their intended purpose), but by reducing inflammation in the arteries and the resultant buildup of soft plaque. 6)
Why do most Americans believe that a diet high in cholesterol will lead to greater risk of heart disease? Because their doctors, the American Heart Association, and The National Institutes of Health, all trusted and reliable sources of health information, have told them repeatedly that this is the case. Why do these groups and individuals believe there is a correlation between consumption of cholesterol and heart disease? Because for many years the best science available indicated that this was the case. The Framingham study and many others that supported their conclusions are scientifically sound and conducted ethically, yet they are limited by the available technology and research methods of their time. Medical research is a slow, methodical process that does not lead to quick answers to complex problems. Public policy decisions are based on need and often cannot wait for incontrovertible truth before being devised and implemented. People are dying from heart disease today and the public will not wait for the decades it may take to prove beyond reasonable doubt exactly what causes it. We are fortunate to live in an age where the latest medical information is available to the general public via the internet. The research is time consuming, and littered with sites promoting ineffective, sometimes dangerous products to cure the disease you are researching, but with a reasoned scientific approach, the information can be found to help us make wise medical and nutritional decisions.