Dietary fat, cooking fat, and breast cancer risk in a multiethnic population.

Our objective was to examine the association between dietary fat intake, cooking fat usage, and breast cancer risk in a population-based, multiethnic, case-control study conducted in the San Francisco Bay area. Intake of total fat and types of fat were assessed with a food frequency questionnaire among 1,703 breast cancer cases diagnosed between 1995 and 1999 and 2,045 controls. In addition, preferred use of fat for cooking was assessed. Unconditional logistic regression was used to estimate odds ratios (ORs) and 95% confidence intervals (CIs). High fat intake was associated with increased risk of breast cancer (highest vs. lowest quartile, adjusted OR = 1.35, 95% CI = 1.10-1.65, P(trend) < 0.01). A positive association was found for oleic acid (OR = 1.55, 95% CI = 1.14-2.10, P(trend) < 0.01) but not for linoleic acid or saturated fat. Risk was increased for women cooking with hydrogenated fats (OR = 1.58, 95% CI = 1.20-2.10) or vegetable/corn oil (rich in linoleic acid; OR = 1.30, 95% CI = 1.06-1.58) compared to women using olive/canola oil (rich in oleic acid). Our results suggest that a low-fat diet may play a role in breast cancer prevention. We speculate that monounsaturated trans fats may have driven the discrepant associations between types of fat and breast cancer.