Diet Low in Fat May Reduce Areas of Density

NEW ORLEANS--Adoption of a low-fat, high-carbohydrate diet reduces thearea of mammographic densities in the breast, a strong risk factor forbreast 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 PreventionStudy Group, a randomized trial of dietary prevention. This controlledanalysis included a subgroup of more than 800 women from the 3,700 womenenrolled in the study.

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

"This prompted us to do a randomized controlled trial in patientswith 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 that60% of the intervention group managed to achieve a diet that was within5% of the target goal.

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

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

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

Age at entry and change in menopausal status from baseline to four yearswere both associated with changes in the area of density, but change inweight was not. After controlling for these variables in multiple regressionanalysis, a low-fat diet still remained significantly associated with areduction in the area of density.

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

Dr. Boyd said that further observation is needed to determine whetherthese changes in areas of density are associated with a reduction in breastcancer risk.