A large study conducted in Sweden and published in the British Journal of Cancer found no overall association between total dietary fat or specific types of dietary fat and risk of breast cancer.
Researchers have long speculated that there could be a link between high-fat diets and risk of breast cancer, but studies have produced inconsistent results. For example, results from a large prospective study published in 2006 suggest that dietary fat is not significantly associated with the risk of postmenopausal breast cancer. Another large prospective study of postmenopausal breast cancer, published early in 2007, reported that higher dietary fat modestly increased the risk of breast cancer.The reasons for these inconsistencies remain uncertain, but may involve aspects of study design or differences in study populations.
To further explore the question of dietary fat and breast cancer, researchers conducted a study among more than 49,000 Swedish women. Study participants were between the ages of 30 and 49 years at the time the study began.
The study collected information about total dietary fat as well as three specific types of fat: monounsaturated, polyunsaturated, and saturated.
During an average follow-up of 13 years, 974 study participants were diagnosed with invasive breast cancer.
- Among all women combined, risk of breast cancer did not vary significantly across levels of total fat or specific types of fat.
- Results were similar in the subset of women under the age of 50: risk of breast cancer did not vary significantly across levels of total fat or specific types of fat.
- In the subset of women over the age of 50, results were somewhat different. Although there was still no statistically significant effect of total or saturated fat intake, women with the highest intakes of monounsatured or polyunsaturated fats had a lower risk of breast cancer than women with the lowest intakes of these types of fats. This is different than what has been observed in some other studies, however, and should be interpreted with caution.
This study adds to the list of large prospective studies that have evaluated the effects of dietary fat on risk of breast cancer. The findings of the current study—which suggest that dietary fat does not increase the risk of breast cancer—are consistent with some, but not all, previous studies.
 Kim EH, Willett WC, Colditz GA et al. Dietary fat and risk of postmenopausal breast cancer in a 20-year follow-up. American Journal of Epidemiology. 2006;164:990-997.
 Thiebaut AC, Kipnis V, Chang SC et al. Dietary fat and postmenopausal invasive breast cancer in the National Institutes of Health-AARP diet and health study cohort. Journal of the National Cancer Institute. 2007;99:451-462.
 Lof M, Sandin S, Lagiou P et al. Dietary fat and breast cancer risk in the Swedish women’s lifestyle and health cohort. British Journal of Cancer. 2007;97:1570-1576.
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