NEW ORLEANS--Adoption of a low-fat, high-carbohydrate diet reduces the area of mammographic densities in the breast, a strong risk factor for breast cancer, Norman F. Boyd, MD, of the Ontario Cancer Institute, Toronto, reported at the American Society for Preventive Oncology meeting.

Dr. Boyd's data came from the Canadian Diet and Breast Cancer Prevention Study Group, a randomized trial of dietary prevention. This controlled analysis included a subgroup of more than 800 women from the 3,700 women enrolled in the study.

Radiologic variations in the appearance of the breast are associated with variations in the risk for breast cancer, Dr. Boyd said. The risk is as much as nine times greater in women aged 50 to 65, who have the most density, especially in proportion to their total breast tissue.

"This prompted us to do a randomized controlled trial in patients with extensive densities," he said.

The intervention group was instructed to decrease dietary fat to 15% of calories and to increase complex carbohydrates. Food records show that 60% of the intervention group managed to achieve a diet that was within 5% of the target goal.

Subjects received mammograms two and four years after randomization, which were digitized and compared to baseline studies. An image processing system measured the area of the breast, the area of density, and the percent of breast area occupied by radiologically dense tissue.

Significant decreases in areas of density were found for women in the intervention group, compared with their own baseline images and with the control group. At two years, the diet intervention group had a reduction of 3 cm² in areas of mammographic density versus a reduction of 1.2 cm² in controls. At four years, the reduction was 7 cm2 for the intervention group and 4 cm2 for controls, Dr. Boyd reported.

In percent of breast area occupied by density, there was no difference at two years, but, at four years, the intervention group had a greater reduction.

Age at entry and change in menopausal status from baseline to four years were both associated with changes in the area of density, but change in weight was not. After controlling for these variables in multiple regression analysis, a low-fat diet still remained significantly associated with a reduction in the area of density.

Women who entered menopause during the study had the greatest reduction in area of mammographic density: 20%, as compared with a 10% reduction in controls. Hormone replacement therapy did not seem to have an influence.

Dr. Boyd said that further observation is needed to determine whether these changes in areas of density are associated with a reduction in breast cancer risk.