Association of dietary intake of fat and fatty acids with risk of breast cancer.

CONTEXT High intakes of fat and specific fatty acids, including total, animal, saturated, polyunsaturated, and trans-unsaturated fats, have been postulated to increase breast cancer risk. OBJECTIVE To determine whether intakes of fat and fatty acids are associated with breast cancer. DESIGN AND SETTING Cohort study (Nurses' Health Study) conducted in the United States beginning in 1976. PARTICIPANTS A total of 88795 women free of cancer in 1980 and followed up for 14 years. MAIN OUTCOME MEASURE Relative risk (RR) of invasive breast cancer for an incremental increase of fat intake, ascertained by food frequency questionnaire in 1980, 1984, 1986, and 1990. RESULTS A total of 2956 women were diagnosed as having breast cancer. Compared with women obtaining 30.1% to 35% of energy from fat, women consuming 20% or less had a multivariate RR of breast cancer of 1.15 (95% confidence interval [CI], 0.73-1.80). In multivariate models, the RR (95% CI) for a 5%-of-energy increase was 0.97 (0.94-1.00) for total fat, 0.98 (0.96-1.01) for animal fat, 0.97 (0.93-1.02) for vegetable fat, 0.94 (0.88-1.01) for saturated fat, 0.91 (0.79-1.04) for polyunsaturated fat, and 0.94 (0.88-1.00) for monounsaturated fat. For a 1% increase in energy from trans-unsaturated fat, the values were 0.92 (0.86-0.98), and for a 0.1% increase in energy from omega-3 fat from fish, the values were 1.09 (1.03-1.16). In a model including fat, protein, and energy, the RR for a 5% increase in total fat, which can be interpreted as the risk of substituting this amount of fat for an equal amount of energy from carbohydrate, was 0.96 (95% CI, 0.93-0.99). In similar models, no significant association of risk was evident with any major types of fat. CONCLUSION We found no evidence that lower intake of total fat or specific major types of fat was associated with a decreased risk of breast cancer.