Replacement of saturated fat by the major dietary polyunsaturated fat linoleic acid reduces blood cholesterol concentrations and the risk of coronary artery disease. However, there is concern that long-term consumption of large amounts of linoleic acid might increase cancer risk. We reviewed the epidemiologic and experimental literature on linoleic acid intake and cancer risk and performed additional meta-analyses of risk estimates from case-control and prospective cohort studies. None of the combined estimates from within-population studies indicated a significantly increased risk of cancer with high compared with low intakes of linoleic acid or polyunsaturated fat. For case-control studies, the combined relative risks were 0.84 (95% CI: 0.71, 1.00) for breast, 0.92 (95% CI: 0.85, 1.08) for colorectal, and 1.27 (95% CI: 0.97, 1.66) for prostate cancer. For prospective cohort studies, combined relative risks were 1.05 (95% CI: 0.83, 1.34) for breast, 0.92 (95% CI: 0.70, 1.22) for colon, and 0.83 (95% CI: 0.56, 1.24) for prostate cancer. Ecologic comparisons of populations showed positive associations between cancer rates and per capita use of animal or saturated fat, but less so with per capita use of vegetable oil or polyunsaturated fat. Controlled studies of coronary artery disease in men did not, except for 1 study, show an increased cancer incidence after consumption of diets with a very high linoleic acid content for several years. Animal experiments indicated that a minimum amount of linoleic acid is required to promote growth of artificially induced tumors in rodents; but above this threshold, linoleic acid did not appear to have a specific tumor-promoting effect. Although current evidence cannot exclude a small increase in risk, it seems unlikely that a high intake of linoleic acid substantially raises the risks of breast, colorectal, or prostate cancer in humans.
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