26 August 2014
When Ronald M Krauss decided, in 2000, to review all the evidence purporting to show that saturated fats cause heart disease, he knew that he was putting his professional career at risk. Krauss is one of the top nutrition experts in the United States, director of atherosclerosis research at Children’s Hospital Oakland Research Institute and adjunct professor of nutritional studies at the University of San Francisco at Berkley. But challenging one of his field’s most sacrosanct beliefs – that the fats in meat, cheese and butter are bad for health – was a near-heretical act.
A few years earlier, when a colleague of Krauss’s had merely tried to speak about his positive findings regarding the high-fat Atkins diet, he was met with jeers and derision. One member of the audience yelled “I am absolutely disgusted that the [government] would waste my money on a study on the Atkins diet” – to the applause of many.
Challenging any of the conventional wisdom on dietary fat has long been a form of professional suicide for nutrition experts. And saturated fats, especially, are the third rail. But Krauss persevered and concluded in 2010, after reviewing all the scientific literature, that saturated fats could not be said to cause heart disease. In March, another group of scientists, including faculty from Cambridge and Harvard, came to the same conclusion after conducting a similar “meta-analysis”. These were stunning results. It seemed that saturated fat, our principal dietary culprit for decades, had been unfairly convicted.
Yet the truth is there never has been solid evidence that these fats cause disease. We only believe this to be true because nutrition policy was derailed over the past half-century by personal ambition, bad science, politics, and bias.
Recipe for success: Vilijamur Stefansson (Corbis)
Our fear of saturated fats began in the 1950s when Ancel Keys, a pathologist at the University of Minnesota, first proposed that they raised cholesterol and therefore caused heart disease. Keys was an aggressive, outsized personality with a talent for persuasion. He found a receptive audience for his “diet-heart hypothesis” among public-health experts who faced a growing emergency: heart disease, a relative rarity three decades earlier, had skyrocketed to be a leading cause of death. Keys managed to implant his idea into the American Heart Association and, in 1961, the group published the first-ever guidelines calling for Americans to cut back on saturated fats, as the best way to fight heart disease.
The US government adopted this view in 1977 and the rest of the world followed. But the evidence backing these guidelines was weak. Mainly, it amounted to Keys’s own “Seven Countries Study”, which purported to show a link between the consumption of saturated fats and heart disease among 13,000 men surveyed in the US, Japan and Europe. Critics have pointed out that this study violated several basic scientific norms. For one, Keys did not choose his countries randomly but instead selected only those likely to prove his beliefs – including Yugoslavia, Finland and Italy – while excluding countries with low rates of heart disease despite diets with a lot of fat – such as France, Switzerland, Sweden and West Germany.
Moreover, due to difficulties in collecting accurate nutrition data, Keys ended up sampling the diets of fewer than 500 men, far from a statistically significant sample. And the study’s star subjects – men on the Greek island of Crete who tilled their fields well into old age and appeared to eat very little meat or cheese – turned out to have been partly sampled during Lent, when the study subjects were foregoing meat and cheese. This must have led Keys to undercount their saturated-fat consumption. These flaws weren’t revealed until much later.
By then, the misimpression left by the erroneous data had become international dogma.
There were subsequent trials, of course. In the 1970s, half a dozen important experiments pitted a diet high in vegetable oil – usually corn or soybean, but not olive oil – against one with more animal fats. But these trials had serious methodological problems: some didn’t control for smoking, for instance, or allowed men to wander in and out of the research group over the course of the experiment. The results were unreliable at best.
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