“ Suppose you were forced to live on a diet of red meat and whole milk. A diet that, all told, was at least 60 percent fat — about half of it saturated. If your first thoughts are of statins and stents, you may want to consider the curious case of the Masai, a nomadic tribe in Kenya and Tanzania.
In the 1960s, a Vanderbilt University scientist named George Mann, M.D., found that Masai men consumed this very diet (supplemented with blood from the cattle they herded). Yet these nomads, who were also very lean, had some of the lowest levels of cholesterol ever measured and were virtually free of heart disease.
Scientists, confused by the finding, argued that the tribe must have certain genetic protections against developing high cholesterol. But when British researchers monitored a group of Masai men who moved to Nairobi and began consuming a more modern diet, they discovered that the men's cholesterol subsequently skyrocketed.
Similar observations were made of the Samburu — another Kenyan tribe — as well as the Fulani of Nigeria. While the findings from these cultures seem to contradict the fact that eating saturated fat leads to heart disease, it may surprise you to know that this "fact" isn't a fact at all. It is, more accurately, a hypothesis from the 1950s that's never been proved.
The first scientific indictment of saturated fat came in 1953. That's the year a physiologist named Ancel Keys, Ph.D., published a highly influential paper titled "Atherosclerosis, a Problem in Newer Public Health." Keys wrote that while the total death rate in the United States was declining, the number of deaths due to heart disease was steadily climbing. And to explain why, he presented a comparison of fat intake and heart disease mortality in six countries: the United States, Canada, Australia, England, Italy, and Japan.
The Americans ate the most fat and had the greatest number of deaths from heart disease; the Japanese ate the least fat and had the fewest deaths from heart disease. The other countries fell neatly in between. The higher the fat intake, according to national diet surveys, the higher the rate of heart disease. And vice versa. Keys called this correlation a "remarkable relationship" and began to publicly hypothesize that consumption of fat causes heart disease. This became known as the diet-heart hypothesis.
At the time, plenty of scientists were skeptical of Keys's assertions. One such critic was Jacob Yerushalmy, Ph.D., founder of the biostatistics graduate program at the University of California at Berkeley. In a 1957 paper, Yerushalmy pointed out that while data from the six countries Keys examined seemed to support the diet-heart hypothesis, statistics were actually available for 22 countries. And when all 22 were analyzed, the apparent link between fat consumption and heart disease disappeared. For example, the death rate from heart disease in Finland was 24 times that of Mexico, even though fat-consumption rates in the two nations were similar.
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The other salient criticism of Keys's study was that he had observed only a correlation between two phenomena, not a clear causative link. So this left open the possibility that something else — unmeasured or unimagined — was leading to heart disease. After all, Americans did eat more fat than the Japanese, but perhaps they also consumed more sugar and white bread, and watched more television.
Despite the apparent flaws in Keys's argument, the diet-heart hypothesis was compelling, and it was soon heavily promoted by the American Heart Association (AHA) and the media. It offered the worried public a highly educated guess as to why the country was in the midst of a heart-disease epidemic. "People should know the facts," Keys said in a 1961 interview with Time magazine, for which he appeared on the cover. "Then if they want to eat themselves to death, let them."
The seven-countries study, published in 1970, is considered Ancel Keys's landmark achievement. It seemed to lend further credence to the diet-heart hypothesis. In this study, Keys reported that in the seven countries he selected — the United States, Japan, Italy, Greece, Yugoslavia, Finland, and the Netherlands — animal-fat intake was a strong predictor of heart attacks over a 5-year period. Just as important, he noted an association between total cholesterol and heart-disease mortality. This prompted him to conclude that the saturated fats in animal foods — and not other types of fat — raise cholesterol and ultimately lead to heart disease.
Naturally, proponents of the diet-heart hypothesis hailed the study as proof that eating saturated fat leads to heart attacks. But the data was far from rock solid. That's because in three countries (Finland, Greece, and Yugoslavia), the correlation wasn't seen.
For example, eastern Finland had five times as many heart-attack fatalities and twice as much heart disease as western Finland, despite only small differences between the two regions in animal-fat intake and cholesterol levels. And while Keys provided that raw data in his report, he glossed over it as a finding. Perhaps a larger problem, though, was his assumption that saturated fat has an unhealthy effect on cholesterol levels.
Trio of saturated fats
Although more than a dozen types of saturated fat exist, humans predominantly consume three: stearic acid, palmitic acid, and lauric acid. This trio comprises almost 95 percent of the saturated fat in a hunk of prime rib, a slice of bacon, or a piece of chicken skin, and nearly 70 percent of that in butter and whole milk.
Today, it's well established that stearic acid has no effect on cholesterol levels. In fact, stearic acid — which is found in high amounts in cocoa as well as animal fat — is converted to a monounsaturated fat called oleic acid in your liver. This is the same heart-healthy fat found in olive oil. As a result, scientists generally regard this saturated fatty acid as either benign or potentially beneficial to your health.
Palmitic and lauric acid, however, are known to raise total cholesterol. But here's what's rarely reported: Research shows that although both of these saturated fatty acids increase LDL ("bad"
cholesterol, they raise HDL ("good"
cholesterol just as much, if not more. And this lowers your risk of heart disease. That's because it's commonly believed that LDL cholesterol lays down plaque on your artery walls, while HDL removes it. So increasing both actually reduces the proportion of bad cholesterol in your blood to the good kind. This may explain why numerous studies have reported that this HDL/LDL ratio is a better predictor of future heart disease than LDL alone.
All of this muddies Keys's claim of a clear connection between saturated-fat intake, cholesterol, and heart disease. If saturated fat doesn't raise cholesterol in such a way that it increases heart-disease risk, then according to the scientific method, the diet-heart hypothesis must be rejected. However, in 1977 it was still a promising idea.
That was the year Congress made it government policy to recommend a low-fat diet, based primarily on the opinions of health experts who supported the diet-heart hypothesis. It was a decision met with much criticism from the scientific community, including the American Medical Association. After all, officially endorsing a low-fat diet could change the eating habits of millions of Americans, and the potential effects of this strategy were widely debated and certainly unproved.
We've spent billions of our tax dollars trying to prove the diet-heart hypothesis. Yet study after study has failed to provide definitive evidence that saturated-fat intake leads to heart disease. The most recent example is the Women's Health Initiative, the government's largest and most expensive ($725 million) diet study yet. The results, published last year, show that a diet low in total fat and saturated fat had no impact in reducing heart-disease and stroke rates in some 20,000 women who had adhered to the regimen for an average of 8 years.
But this paper, like many others, plays down its own findings and instead points to four studies that, many years ago, apparently did find a link between saturated fat and heart disease. Because of this, it's worth taking a closer look at each.