"Soft" science? Fat's health impacts are often oversimplified, Science news feature contends

Media Note: This release describes a Science news feature by award-winning journalist Gary Taubes. His report examines complex scientific issues, and does not advocate any particular nutritional regimen. Dietary guidance should be provided only by health-care professionals.

"Mainstream nutritional science has demonized dietary fat," a Science news article reports in the 30 March, 2001 issue. "Yet, 50 years and hundreds of millions of dollars of research have failed to prove that eating a low-fat diet will help you live longer."

Reporter Gary Taubes spent over a year researching the article and based his conclusions on interviews with over 150 sources. Taubes emphasizes that "no one is recommending that people run out and eat butter and lard instead of vegetables."

But, his news report contends, "The data remain ambiguous as to whether low-fat diets will benefit healthy Americans." Moreover, Taubes reports, dire warnings about dietary fat may have encouraged a shift to high-carbohydrate diets, "which may be no better-perhaps even worse-than high-fat diets."

America's fear of fat emerged some 50 years ago, when it quickly replaced malnutrition as the nation's top dietary concern. After World War II, Taubes explains, a major increase in coronary heart disease prompted researchers like Ancel Keys of the University of Minnesota, Twin Cities, to call for reduced fat intake.

In fact, since the 1970s, Americans' average fat intake has dropped from over 40 percent of total calories to 34 percent, and cholesterol levels are lower, too. While fewer people are dying from heart disease, the incidence of heart disease has not declined: Between 1979 and 1996, the number of medical procedures for heart disease increased from 1.2 million to 5.4 million a year, the American Heart Association reports.

Since the early 1980s, obesity has increased dramatically in America, from 14 percent of the population to over 22 percent, and diabetes is also on the rise. The incidence of obesity and diabetes, which both increase heart disease risks, began to rise about the same time that "the government began bombarding Americans with the low-fat message," Taubes writes.

What gives fat a bad name? Dietary fat-especially the hard, saturated fat in meat and dairy products-can increase blood cholesterol levels. More cholesterol in the bloodstream may increase the risk of clogged arteries, or atherosclerosis, which raises the likelihood of coronary artery disease, heart attacks and premature death. But this once-simple proposition-dietary fat raises cholesterol, which in turn raises heart disease risks-remains stubbornly unproven, according to Taubes.

The individual steps in this process have all been scientifically proven, Taubes says. But, researchers have not demonstrated that low-fat diets extend the lives of healthy people, he adds. As Taubes reports, complexities introduced by the different types of cholesterol and different types of fats, and the remarkable diversity of human diets, has made it virtually impossible to predict that a single dietary regimen will benefit every individual who tries it.

He also points out that diet is a trade-off: individuals who eat excessive amounts of dietary fat, for instance, usually eat very little fresh fruits and vegetables. As a result, he says, studies that seemed to indicate that eating too much fat was bad for health might actually have been demonstrating that a lack of fruits and vegetables was the culprit.

A new generation of pharmaceuticals do "reduce serum cholesterol levels dramatically, and they prevent heart attacks," according to Taubes. Bu

t, the notion that eating less fat contributes to a healthier, longer life "has remained stubbornly ambiguous," he adds. "The science of fat and cholesterol has evolved from a simple story into a very complicated one."

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Media Note: This Science article does not necessarily reflect the opinions of the American Association for the Advancement of Science (AAAS), the journal's non-profit publisher.