Low-fat diet won’t reduce health risks

Overturning three decades of conventional wisdom, a new study of low-fat diets in nearly 50,000 healthy older women has shown that reducing fat intake alone does not significantly reduce the risk of heart disease, stroke, breast cancer or colorectal cancer, researchers reported Tuesday.

Results from the same study reported last month also showed that reducing fats without reducing calories does not lead to significant weight loss.

“Just switching to low-fat foods is not likely to yield much health benefit in most women,” said Marcia Stefanick, a professor of medicine at the Stanford Prevention Research Center, chairwoman of the steering committee for the Women’s Health Initiative study.

“Rather than trying to eat ‘low-fat,’ ” she said, “women should focus on reducing saturated fats and trans fats,” the so-called “bad” fats, while maintaining their intake of “good” fats, such as vegetable, olive and fish oils.

“Nutrition knowledge has progressed dramatically since the study began,” said Mara Vitolins, a professor of public health sciences at Wake Forest University Baptist Medical Center in Winston-Salem, N.C., and a study co-author. “Today we know that reducing total fat may not be enough – we need to focus on the types of fat we eat.”

The 13-year study, whose results will be reported today in three papers in the Journal of the American Medical Association, did hint at some possible benefits from reducing fat intake.

Women on the low-fat diet who had the highest consumption of fats at the beginning of the study showed the biggest decrease in breast cancer risk. And those who achieved the lowest rate of fat consumption showed the lowest risk of heart disease. And those who reduced fat intake had a lower incidence of polyps, generally considered to be a precursor of colorectal cancer.

In each of those cases, however, the reductions were not statistically significant, meaning that they could have occurred by chance.

In part, that may be because the women in the study have only been followed for eight years, on average, said Dr. Rowan T. Chlebowski of the Los Angeles Biomedical Institute in Torrance, Calif., a study co-author. “I’m cautiously optimistic that, with a few more years of follow-up, there may be something,” particularly for breast cancer, he said.

The study also found that the diet, which included increased consumption of carbohydrates and grains, is safe and healthful – contradicting the claims of proponents of low-carbohydrate diets, such as the Atkins diet, that high carbs increase the risk of diabetes.