Low-fat dietary pattern and breast cancer mortality in the Women's Health Initiative randomized controlled trial

Purpose: Earlier Women's Health Initiative Dietary Modification trial findings suggested that a low-fat eating pattern may reduce breast cancers with greater mortality. Therefore, as a primary outcome-related analysis from a randomized prevention trial, we examined the long-term influence of this intervention on deaths as a result of and after breast cancer during 8.5 years (median) of dietary intervention and cumulatively for all breast cancers diagnosed during 16.1 years (median) of follow-up. Patients and Methods: The trial randomly assigned 48,835 postmenopausal women with normal mammograms and without prior breast cancer from 1993 to 1998 at 40 US clinical centers to a dietary intervention with goals of a reduction of fat intake to 20 % of energy and an increased intake of fruits, vegetables, and grains (40 % ; n = 19,541) or to a usual diet comparison (60 % ; n = 29,294). Results: In the dietary group, fat intake and body weight decreased (all P > .001). During the 8.5-year dietary intervention, with 1,764 incident breast cancers, fewer deaths occurred as a result of breast cancer in the dietary group, which was not statistically significant (27 deaths [0.016 % per year] v 61 deaths [0.024 % per year]; hazard ratio [HR], 0.67; 95 % CI, 0.43 to 1.06; P = .08). During the same period, deaths after breast cancer (n = 134) were significantly reduced (40 deaths [0.025 % per year] v 94 deaths [0.038 % per year]; HR, 0.65; 95 % CI, 0.45 to 0.94; P = .02) by the dietary intervention. During the 16.1-year follow-up, with 3,030 incident breast cancers, deaths after breast cancer also were significantly reduced (234 deaths [0.085 % per year] v 443 deaths [0.11 % per year]; HR, 0.82; 95 % CI, 0.70 to 0.96; P = .01) in the dietary group. Conclusion: Compared with a usual diet comparison group, a low-fat dietary pattern led to a lower incidence of deaths after breast cancer.