A new long-term prospective study has reported that a low-fat, high-carbohydrate diet does not reduce the likelihood of breast cancer among women considered high risk because of dense breasts. Population studies and experiments using animals suggest that dietary fat may influence risk of breast cancer. The study included 4,690 women with extensive mammographic density who were assigned randomly to a dietary intervention group or a comparison group. The intervention group received intensive dietary counseling with the goal of reducing fat intake to 15% of total calories and increasing carbohydrate intake to 65% of calories. Actual intakes were assessed throughout the trial using food diaries.

Women in the intervention group reduced their percentage of calories from fat from approximately 30% at the outset of the study to 20% after being assigned to the dietary intervention group. Intervention group participants maintained levels of fat intake that were 9% to 10% lower than the comparison group throughout the trial. The women were followed for an average of 10 years.

A total of 118 invasive breast cancers were diagnosed in the intervention group compared to 102 in the comparison group during the study period. However, this difference was not statistically significant. Analysis of participant food records demonstrated that the level of fat consumed at baseline or during the study was not linked to risk of breast cancer. However, greater body weight and lower carbohydrate intake were found to be associated with an increased risk of estrogen receptor positive (ER+) breast cancer. The authors conclude that a sustained reduction in dietary fat intake did not appear to reduce the risk of breast cancer in women with dense breasts.

Comments regarding the study

The study results are not surprising since breast cancer risk has been shown to be associated with specific types of fat and carbohydrates, rather than overall fat or carbohydrate intake. Please see our articles on breast density and how to optimize your diet.