Fats, particularly highly saturated animal varieties, are bad for us. We all know this even as we guiltily order a double cheeseburger at a fast-food restaurant or place a well-marbled steak on the backyard barbecue.

But how do we know they are bad for us? Well, you might reply, nutritionists, doctors and about every official report you read say that fats cause obesity, cholesterol buildup, increased heart disease and even cancer. Yes, they do, but is it true?

Gary Taubes has published a lengthy review of how dietary fats came by their bad reputation, and how much it is actually deserved, in the March 30 issue of Science. What he uncovered may surprise you.

In 1984, the National Institutes of Health urged Americans to cut down on their fat intake, and the president of the American Heart Association told Time magazine that if everyone went along, “we will have atherosclerosis [arterial blockage by cholesterol] conquered by the year 2000.”

The U.S. Surgeon General’s Office issued a report the same year declaring fat the single most unwholesome component of the diet and undertook a massive study in 1988 to prove everyone’s dire predictions were correct. In 1999, with little fanfare, the study was killed with no other explanation than it had proved “too complicated.”

After 11 years and millions of dollars, there was no official report, press release or announcement to the public. Taubes quotes Bill Harlan of the NIH, and a member of the study’s oversight committee, that the real reason for the termination was that the study began with a preconceived opinion as to the results, but that science was not giving the answer they wanted or expected.

One long-cherished belief was that saturated fats from meat and dairy products elevate blood cholesterol leading to atherosclerosis and heart disease. But countless studies have failed to show healthy individuals benefit from low-fat diets, says Taubes, and the shift to high-carbohydrate diets may be no better, or even worse, than high-fat diets. Death rates due to heart disease have declined along with fat intake, but its incidence has not. A 10-year study published in a 1998 issue of The New England Journal of Medicine suggests that the declining death rates are largely due to better medical treatments and not diet.

Other statistics argue against the benefits of a low-fat diet such as the increase in national obesity from 14 to 22 percent in the years since Americans were urged to cut down on fats. The incidence of diabetes has followed roughly the same path. The Harvard School of Public Health has conducted a massive three-part study over 20 years on 300,000 Americans with $100 million provided by the NIH. To quote Taubes directly, “The results show that total fat consumed has no relation to heart disease risk; that monosaturated fats like olive oil lower risk; and that saturated fats are little worse, if at all, than the pasta and other carbohydrates that the Food Guide Pyramid suggests be eaten copiously.” Ironically the NIH has opted not to alter its low dietary fat guidelines to reflect the results of the study it funded.

So how did dietary fat get such a bad reputation? After World War II, says Taubes, an epidemic of coronary heart disease swept through middle-aged men and, in 1952, Ancel Keys of the University of Minnesota announced that dietary fat was the cause. Time-consuming surveys of large segments of the population would be the only way to test this hypothesis but, says Taubes, the public, politicians and popular press were unwilling to wait for the results.

Also an anti-fat mentality arose in the early 1960s among the counterculture movement that tied the medical establishment to the food industry. It was in this climate that Sen. George McGovern headed a Select Committee on Nutrition that, according to Taubes, single-handedly changed the nation’s attitude toward what it consumed and transformed the dietary fat hypothesis into dogma. The McGovern committee relied heavily on Nathan Pritikin’s very low-fat diets and hired a former newspaper reporter, Nick Mottern, to write its report. He, in turn, essentially ignored the scientific literature and almost exclusively used the work of Harvard Public Health nutritionist Mark Hegsted for all scientific input on dietary fat. Hegsted regarded dietary fat as an equal health risk to tobacco and intimated that scientists who disagreed were in the pocket of the dairy and beef industries. The McGovern report was released in 1977 urging huge cuts in dietary fat. The reaction was mixed and sharp.