Remember the low-fat-diet? Highly popular in the 1980s and 1990s, it was finally pushed out of the limelight by competitive eating regimens such as the Mediterranean diet. That the low-fat diet wasn’t particularly healthy hadn’t yet been discovered. But its official blessing for decades by the governments of both the U.S. and UK represents a subversion of science by political forces that overlook evidence and abandon reason.
The low-fat diet was born in a 1977 report from a U.S. government committee chaired by Senator George McGovern, which had become aware of research purportedly linking excessive fat in the diet to killer diseases such as coronary heart disease and cancer. The committee hoped that its report would do as much for diet and chronic disease as the earlier Surgeon General’s report had done for smoking and lung cancer.
The hypothesis that eating too much saturated fat results in heart disease, caused by narrowing of the coronary arteries, was formulated by American physiologist Ancel Keys in the 1950s. Keys’ own epidemiological study, conducted in seven different countries, initially confirmed his hypothesis. But many other studies failed to corroborate the diet-heart hypothesis, and Keys’ data itself no longer substantiated it 25 years later. Double-blind clinical trials which, unlike epidemiological studies are able to establish causation, also gave results in conflict with the hypothesis.
Although it was found that eating less saturated fat could lower cholesterol levels, a growing body of evidence showed that it didn’t help to ward off heart attacks or prolong life spans. Yet Senator McGovern’s committee forged ahead regardless. The results of all the epidemiological studies and major clinical trials that refuted the diet-heart hypothesis were simply ignored – a classic case of science being trampled on by politics.
The McGovern committee’s report turned the mistaken hypothesis into nutritional dogma by drawing up a detailed set of dietary guidelines for the American public. After heated political wrangling with other government agencies, the USDA (U.S. Department of Agriculture) formalized the guidelines in 1980, effectively sanctioning the first ever, official low-fat diet. The UK followed suit a few years later.
While the guidelines erroneously linked high consumption of saturated fat to heart disease, they did concede that what constitutes a healthy level of fat in the diet was controversial. The guidelines recommended lowering intake of high-fat foods such as eggs and butter; boosting consumption of fruits, vegetables, whole grains, poultry and fish; and eating fewer foods high in sugar and salt.
With government endorsement, the low-fat diet quickly became accepted around the world. It was difficult back then even to find cookbooks that didn’t extol the virtues of the diet. Unfortunately for the public, the diet promoted to conquer one disease contributed to another – obesity – because it replaced fat with refined carbohydrates. And it wasn’t suitable for everyone.
This first became evident in the largest ever, long-term clinical trial of the low-fat diet, known as the Women’s Health Initiative. But, just like the earlier studies that led to the creation of the diet, the trial again showed that the diet-heart hypothesis didn’t hold up, at least for women. After eight years, the low-fat diet was found to have had no effect on heart disease or deaths from the disease. Worse still, in a short-term study of the low-fat diet in U.S. Boeing employees, women who had followed the low-fat diet appeared to have actually increased their risk for heart disease.
A UN review of available data in 2008 concluded that several clinical trials of the diet “have not found evidence for beneficial effects of low-fat diets,” and commented that there wasn’t any convincing evidence either for any significant connection between dietary fat and coronary heart disease or cancer.
Today the diet-heart hypothesis is no longer widely accepted and nutritional science is beginning to regain the ground taken over by politics. But it has taken over 60 years for this attack on science to be repulsed.
Next week: How Hype is Hurting Science