COHORT STUDIES OF FAT INTAKE AND THE RISK OF BREAST-CANCER - A POOLEDANALYSIS

Background. Experiments in animals, international correlation comparis ons, and case-control studies support an association between dietary f at intake and the incidence of breast cancer. Most cohort studies do n ot corroborate the association, but they have been criticized for invo lving small numbers of cases, homogeneous fat intake, and measurement errors in estimates of fat intake. Methods. We identified seven prospe ctive studies in four countries that met specific criteria and analyze d the primary data in a standardized manner. Pooled estimates of the r elation of fat intake to the risk of breast cancer were calculated, an d data from study-specific validation studies were used to adjust the results for measurement error. Results. Information about 4980 cases f rom studies including 337,819 women was available. When women in the h ighest quintile of energy-adjusted total fat intake were compared with women in the lowest quintile, the multivariate pooled relative risk o f breast cancer was 1.05 (95 percent confidence interval, 0.94 to 1.16 ). Relative risks for saturated, monounsaturated, and polyunsaturated fat and for cholesterol, considered individually, were also close to u nity. There was little overall association between the percentage of e nergy intake from fat and the risk of breast cancer, even among women whose energy intake from fat was less than 20 percent. Correcting for error in the measurement of nutrient intake did not materially alter t hese findings. Conclusions. We found no evidence of a positive associa tion between total dietary fat intake and the risk of breast cancer. T here was no reduction in risk even among women whose energy intake fro m fat was less than 20 percent of total energy intake. in the context of the Western lifestyle, lowering the total intake of fat in midlife is unlikely to reduce the risk of breast cancer substantially.