By Renee Twombly
New clinical trial results linking a low-fat diet to a reduced risk of breast cancer are quite substantial and should be taken seriously by women wanting to help prevent the disease, according to the author of an editorial in the Journal of the American Medical Association.

The commentary, made by Aman Buzdar, M.D., a professor in M. D. Anderson’s Department of Breast Medical Oncology, appears in the publication’s Feb. 8 issue, along with the study itself. The 15-year clinical trial, sponsored by the Women’s Health Initiative (WHI), involved 49,000 women from across the United States.

Some researchers argue that the results are not “statistically significant” because a statistical goal set by study investigators was not met. “The conventional way to look at any data is that findings are considered real (statistically significant) if there is 95% probability that results are not by chance. The finding of this study didn’t meet those rigorous criteria. Instead there is a 91% probability that these findings are real. It failed the magic 95% probability rule, Buzdar says. “And that’s about as close as they got. What this tells me is that, for the first time, women have something they can do that may help them modify their cancer risk.”

Women decrease fat, increase vegetables and grains

In the WIH study, 40 clinical centers throughout the United States enrolled women, ages 50-79, who had not been diagnosed with breast cancer. Neither group was asked to reduce their calorie intake.

The women were asked to do one of the following:

Change their diet – 40% (19,541 women) agreed to:

Reduce fat to 20% of calorie intake
Eat five daily servings of vegetables
Eat six daily servings of grain
Not change their diet – 60% (29,294 women) agreed not to make any dietary changes.

Past studies do not determine dietary influence

The new study is the most rigorous so far, Buzdar says. A number of studies have found that, as a group, women who eat a diet low in fat develop fewer cases of invasive breast cancer than women who eat more fat. Other studies have further concluded that a low-fat diet protects against cancer recurrence after a woman has been treated. 

But the problem with most of the earlier studies, Buzdar says, is that they all have been “retrospective” − meaning that researchers looked at women who did, or did not, develop cancer, and then they tried to understand, through questionnaires, what lifestyle choices might have contributed to whether a woman developed cancer.

What is needed, he says, is a clinical trial that is prospective, randomized and controlled. That is, a study like the WIH trial that follows women for a number of years to see if they develop breast cancer and that arbitrarily places participants in one of two groups. One group would eat a low-fat diet. The other, a “control” group, would have no dietary restrictions. At the end of the study, outcomes between the groups would be compared.

Buzdar concludes that women should take a “glass half full” approach to the latest findings, recognizing that it may be within their power to ward off breast cancer.