NEW YORK, Mar 09 (Reuters Health) -- Contrary to conventional theory, a large, long-term study finds no association between levels of dietary fat intake and a woman's risk for breast cancer.

``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,'' conclude a team of researchers led by Dr. Michelle Holmes of Harvard Medical School in Boston, Massachusetts. Their findings are reported in the March 10th issue of The Journal of the American Medical Association.

Prior studies have produced conflicting results regarding the relationship, if any, between dietary fat and breast cancer. Still, some experts have recommended that women cut their fat intake to less than 20% of daily energy requirements to help reduce their risk for breast cancer.

In their study, one of the longest and largest to date, Holmes' team tracked the 14-year breast cancer incidence of nearly 89,000 women followed as part of the ongoing Nurses' Health Study. As part of the research, each of the women completed detailed dietary questionnaires every 2 years.

The authors found ``no increased risk of breast cancer with increased intake of animal fat, polyunsaturated fat, saturated fat, or trans-unsaturated fat.'' These results held even when the researchers adjusted their findings for factors such as obesity; intakes of folate, fiber, or vitamin E; and utilization of mammography screening.

Based on these results, the Boston team concludes that ''reductions in total fat intake during midlife are unlikely to prevent breast cancer and should receive less emphasis.'' However, they point out that high fat consumption can still pose a substantial risk to cardiovascular health, and advise that ''women's decision(s) about fat intake should be guided primarily by risk of heart disease.''

SOURCE: The Journal of the American Medical Association 1999;281:914-920.

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