Eating a high-fat diet may slightly increase the risk of developing invasive breast cancer in some middle-aged women.

Researchers followed more than 188,000 postmenopausal women who gave information about 124 foods they ate for a study by the U.S. National Institutes of Health.

Over an average of 4.4 years of follow up, there were 3,501 cases of breast cancer, Anne Thiébaut of the institute's nutritional epidemiology branch and her colleagues report in Wednesday's issue of the Journal of the National Cancer Institute.

Rates of breast cancer were 11 per cent to 22 per cent higher for women who got about 40 per cent of their calories from fat, compared with those who consumed 20 per cent of their calories from fat, the researchers found.

"In this large prospective cohort with a wide range of fat intake, dietary fat intake was directly associated with the risk of postmenopausal invasive breast cancer," the team concluded.

Although Thiébaut's study corrected for measurement error in fat and energy intakes, which strengthens the link, focusing on fat intake may not be the best strategy for preventing breast cancer, according to a commentary accompanying the study.

In it, Drs. Stephanie Smith-Warner and Meir Stampfer of the Harvard School of Public Health said reducing the amount of body fat would have a greater impact on preventing breast cancer rather than focusing solely on reducing fat in the diet.

Smith-Warner and Stampfer suggest focusing on controlling body fat by eating fewer calories and exercising.