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.