Fat

Fat gets a bad rap. Everyone knows that “fat makes you fat” and fat “clogs your arteries”. For more than 50 years this has been the conventional wisdom from both the medical community and the government. In reality, both ideas are myths. Unfortunately these ideas have become so ingrained in our culture that is is quite difficult to convince people otherwise. For many people this is the major obstacle preventing people from considering a ketogenic diet.

First, consider the problem of overweight and obesity. Most people, doctors included, believe that the cause of obesity is consuming more calories than you expend. This is the “calories-in, calories-out” model or CICO model. In the CICO model fat is the villain because it is more calorie dense at 9 calories per gram compared to 4 calories per gram for both protein and carbohydrate. Within this model the obvious strategy is to cut back on fat intake to reduce total calories. This idea resonates because it offers a simple strategy with which to approach weight loss.

The cause of obesity is not settled science. Stating that obesity is caused by a caloric surplus is like saying that Bill Gates is rich because he makes more money than he spends. Both statements are true but it doesn’t explain why people become obese or why Bill Gates became rich. I believe there’s a different explanation for the cause of obesity but I’ll address that in another post.

In December 1955 Dwight Eisenhower was playing golf in Denver, Colorado. After lunch he began having “indigestion”. He thought it was from the hamburger with onions. This lasted into the night and his personal physician was summoned. He was treated with pain medication with some relief but the pain persisted until the next morning. An ECG was performed and it was clear that he was having a heart attack. Back in the 50’s there were no effective treatments for a heart attack and the standard of care was hospitalization and strict bed-rest. Eisenhower was out of the Oval Office for about 10 days and the details of his hospital stay were widely documented in the media. This event together with other media reports led to the popular belief that there was an epidemic of heart disease among middle-aged American men.

Enter Ancel Keys. A strong-willed opinionated physiologist from Minnesota. You might consider him the “founder” of the diet-heart hypothesis. It had been known for years that cholesterol was present in atherosclerotic plaque. Keys was convinced that diet played a role in causing elevated cholesterol which, in turn, caused heart disease. Note that this diet-heart hypothesis is a three part theory. First it postulates that a high level of cholesterol in the blood is the cause of atherosclerosis. Second it states that some dietary factor is responsible for the elevated cholesterol. Thirdly, it is proposed that a dietary manipulation to lower the blood cholesterol level should decrease the risk of heart disease. I would argue that none of these hypotheses have been definitively proven.

It is interesting that in Keys’ 1953 article he discussed the fact that dietary cholesterol has virtually no effect on serum cholesterol: “The total cholesterol concentration in the serum of man is substantially independent of the dietary cholesterol intake over the whole range of possible human diets.” Think about that. It was known in the 1950’s that cholesterol in the diet did not affect blood cholesterol levels. How is is possible that the medical community recommended restriction of dietary cholesterol for the ensuing 50+ years?

So if it isn’t the dietary cholesterol that raises serum cholesterol then what is the culprit? Keys was convinced that rich fatty food (enjoyed by the upper class) was the cause of heart disease and he targeted saturated fat as the villain. Generally speaking, saturated fat is most commonly found in animal fat: meat, dairy, etc. Keys and his wife loved to travel, especially to Italy and the Mediterranean (where he later retired). In his travels he put together statistical data comparing the incidence of heart disease in various countries and correlated it with the corresponding fat intake in those countries. In its first iteration he published this graph in 1953.

Keys, A Journal of The Mount Sinai Hospital, 1952, 20 (2), 118-139

Looks convincing. Over the ensuing years he pursued this diet-heart hypothesis with a vengeance. Keys became an influential member of the American Heart Association’s (AHA) nutritional committee. In 1961 the AHA became the first major medical association to make a formal recommendation to reduce saturated fat in the diet in the interest of lowering cholesterol and preventing heart disease. The idea snowballed. The metaphor that fat “clogs your arteries” was, and is very powerful. The public was sold.

It is interesting how science is influenced by the technology of the day. Total cholesterol was just about the only blood lipid that was readily measurable at the time. It turn out the Keys’ wife Margaret was quite skilled in running the assay for total cholesterol on blood samples. What could be a better “working vacation” than to travel around the world, check people’s cholesterol and survey them about their diet? This was the state of epidemiology at the time.

A word about epidemiology. This is the study of correlations or associations between a disease state and other factors. The most important thing to remember about these types of studies is that they DO NOT demonstrate causation. Their purpose is to generate a hypothesis which can later be tested with an interventional trial. A tremendous portion of the nutrition literature is based on epidemiological studies. We’ve all seen these studies in headlines. “Coffee causes cancer” - “Coffee cures cancer” - “Eggs cause heart disease” - You know the drill. This is WEAK science. The only times that these studies of associations between a disease state and an environmental factor have any significant value is when there is either a tremendous association or when the association is trivial. Probably the best and well known example of a useful epidemiological association is that between cigarette smoking and lung cancer. It was found that there was a 30 fold increase in the chance of lung cancer among cigarette smokers. That is a compelling association suggesting genuine causation. Compare that to the association of processed red eat intake and colon cancer. You might be about twice as likely to get colon cancer if you consume a diet high in processed red meats. This is a weak association that would require an interventional study to prove causality. To extend the point, if an association is NOT demonstrated above a certain level (at least 2-4 fold) it is extremely unlikely that any causal association exists. In this sense a study showing no or only a very weak association between factors probably rules out causality.

President Eisenhower became obsessed with his cholesterol after his heart attack. He followed a strict low fat, low cholesterol diet to no avail. Toward the end of his term his doctors were lying to him about his cholesterol levels to keep him from becoming enraged. Shortly after Eisenhower left office Ancel Keys was featured on the cover of Time Magazine

In 1977 George McGovern’s senate committee came up with the first dietary guidelines sanctioned by the US government. These guidelines were heavily influenced by the same cadre of scientists that were on board with the diet-heart hypothesis led by Harvard epidemiologist Mark Hegstead. Based on the opinions (not science) of these epidemiologists the committee published a set of comprehensive guidelines that would influence school lunches, hospital meals, prison, military and nursing home meals. A centerpiece of these recommendations was the advice to reduce the intake of saturated fat in the diet. With the reduction of fat there was a concomitant increase in carbohydrate intake. Only recently did it come to light that years before the McGovern committee Dr. Hegstead and two of his associates at Harvard received a payoff from the sugar industry to publish a review in the New England Journal of Medicine. This was a favorable review of sugar and implicated saturated fat as a cause of heart disease.

Within a few years these recommendations morphed into the Food Pyramid with which we are all familiar. The Food Pyramid then ignited the low fat craze. The food industry responded with zeal and generated a multitude of low fat food products. The key ingredient typically substituted for fat: sugar. In addition vegetable oils and margarine were recommended as substitutes for animal fat. This turned out to be the largest uncontrolled dietary experiment in history.

The American public responded with enthusiasm. Sales of low fat “heart healthy” food soared. Take a look at the graph on the prevalence of overweight and obesity. There’s a prominent inflection point right around 1980. Coincident with the low fat craze was a marked rise in the incidence of overweight and obesity. This is an association (epidemiology) and does not constitute proof that these dietary recommendations were the cause of this epidemic. It does however, look quite suspicious.

So, are there any scientific studies that actually looked at whether a low fat diet is beneficial? The Women’s Health Initiative was one of the better examples of a large dietary intervention trial. Just over 48,000 post-menopausal women were enrolled in this study between 1993 and 1998. They were separated into a group that followed a low fat diet (20% reduction in fat with increased fruits and vegetables) and a control group on a standard diet. They were followed for about eight years and disease incidence was recorded. Remember, this was a prospective (going forward in time) interventional trial, not an observational epidemiological study.

The bottom line was that after 8 years the intervention group had lower cholesterol levels but this did NOT translate into a lower incidence of cardiovascular disease.

Another interesting study was the Minnesota Coronary Experiment. This study was conducted in Minnesota in a nursing home and several mental institutions where diets could be rigorously controlled. You couldn’t do this kind of experiment these days because of ethical concerns. The control group was fed a standard fat diet and in the intervention group saturated fat was replaced by polyunsaturated vegetable oils. The groups were followed for about 7 years. At the end of the study there was no improvement in cardiovascular outcomes and the intervention group had a higher incidence of cancer.

Probably the most interesting part of this story is the fact that this study initially went unpublished. It took 16 years before all of the data saw the light of day. When one of the authors was asked about why it went unpublished the answer was that they were “disappointed” in the result. This is research malpractice. To intentionally withhold a significant scientific finding because it didn’t fit your hypothesis or ideology is criminal. This never made the press in any meaningful way.

Another example is the Sidney Diet Heart Study. this study enrolled 458 men age 30 to 59 who had recently been admitted to the hospital with either a heart attack or unstable cardiac symptoms between 1966 and 1973 in Australia. The intervention group decreased their saturated fat intake to < 10% of food energy and polyunsaturated fatty acid (Safflower oil) was increased to 15% of food energy. No dietary changes were made in the control group. After 7 years the dietary intervention had “increased the rates of death from all causes, coronary heart disease, and cardiovascular disease.”

A large meta-analysis (pooled data from many epidemiological studies) of saturated fat and heart disease did NOT show any association between saturated fat intake and cardiovascular disease. Remember, if you can’t demonstrate a strong association then it is unlikely there is any effect at all. I believe that these studies, taken together “exonerate” saturated fat as a cause of cardiovascular disease and furthermore dispel the idea that substituting vegetable oil for saturated fat is beneficial for cardiovascular health. Mainstream medicine and popular culture however, still embrace this idea that dietary fat causes heart disease.

Only this year has there been an attempt on the part of some medical societies to walk back the limitation on saturated fat. Here’s a graphic from a recent Journal of the American College of Cardiology article addressing this issue.

It’s refreshing to see this coming from the American College of Cardiology but the American Heart Association, on the other hand, has essentially doubled-down on the low fat story. Old, bad ideas take a long time to die.