Low-Fat Diet May Not Cut Cancer Risk

Feb. 7, 2006 - A study of almost 50,000 postmenopausal women shows little evidence that following a low-fat diet reduces the risk of breast cancer, colorectal cancer, or even heart disease.

Researchers stopped short of calling findings from the $415 million Women's Health Initiative (WHI) Dietary Modification Trial disappointing, saying, instead, that longer follow-up of the women in the study may prove the disease-fighting benefits of a low-fat diet.

But significant reductions in breast cancer, colorectal cancer, and heart disease were not seen in the majority of women in the study who ate low-fat diets high in fruits, vegetables, and grains for an average of eight years.

Nonetheless, investigators at a news conference today called the findings consistent with current disease-prevention guidelines.

"The results of this study do not change established recommendations for disease prevention," says National Heart, Lung, and Blood Institute Director Elizabeth G. Nabel, MD.

"Women should continue to get regular mammograms and screenings for colorectal cancer, and work with their doctors to reduce their risks for heart disease, including following a diet low in saturated fat, trans fat, and cholesterol."

Largest Low-Fat Trial

Results from this study, the largest intervention study to evaluate low-fat diets, are reported in The Journal of the American Medical Association.

From 1993 to 2005, the study included 48,835 postmenopausal women aged 50 to 79 who either agreed to follow a low-fat diet or were told to continue eating as they had been.

By the end of the first year, the low-fat-diet group had reduced their average total fat intake to 24% of their daily calories. By the sixth year of the study, 29% of their daily calories came from fat.

In contrast, fat accounted for roughly 35% of daily calories consumed by women in the nonintervention group during the first year of the study and 37% of daily calories in the study's sixth year.

Reason for Optimism?

During an average of eight years of follow-up, women who reduced their total fat intake did not have reduced risk for colorectal cancer. The researchers write that whether greater adherence to the low-fat diet, longer follow-up, and starting a low-fat diet earlier on would have made a difference to the risk for colorectal cancer "remain unanswered questions."

Women in the low-fat group had a 9% lower risk of breast cancer than women who made no dietary changes, which is not a significant reduction. But Nabel and other experts say there is reason for optimism in the findings.

And reductions in risk were greatest among women who had cut their overall fat intake and saturated fat intake the most. The researchers say longer follow-up may show a clearer difference.

"It is best to say at this point that we have evidence of some relationship between breast cancer risk and (dietary) fat content," says the study's principal researcher, Ross Prentice, PhD. "But we should probably leave it at that."