Adopting a low-fat diet at midlife or later probably won’t reduce a woman’s risk of breast cancer, a study suggests.

Pooling and analyzing the results of seven previous studies involving a total of 337,819 women, mostly middle-aged or older, scientists found that the amount of fat in the participants’ diets had no effect on their risk of breast cancer.

The researchers in the earlier studies didn’t find out how long the women had been on their diets, so the results don’t rule out the possibility that women who have avoided fat for most of their lives run a lower breast cancer risk.

Indeed, other studies suggest that if a low-fat diet can influence that risk it would have to be adopted in childhood or adolescence to affect the processes that lead to cancer.

“There are other, very good reasons to stick to a diet which is relatively low in red meat, and low in high-fat dairy products, and high in fruits and vegetables,” said Dr. David Hunter, citing evidence of reduced risk for heart disease and colorectal cancer. “Unfortunately, it doesn’t appear that breast cancer protection, at least in midlife, is one of those good reasons.”

Hunter other scientists reported the work in today’s issue of the New England Journal of Medicine.

The idea that lowering fat intake during middle age could help protect against breast cancer had appeared to be promising, but it shows “less promise all the time,” said Robert Smith, an epidemiologist and senior director for detection and treatment at the American Cancer Society.