(As reported 3/10/99)
Reversing a popular medical theory, a new study says that a low-fat diet doesn't decrease a woman's risk of getting breast cancer. CBS News Health Correspondent Dr. Emily Senay reports.
Doctors have theorized that eating lots of fat increases breast-cancer risk. They have based their thinking on animal studies, international comparisons and studies of women who developed breast cancer and women who didn't.
The new study, published in Wednesday's Journal of the American Medical Association, tracked 88,795 women in the continuing Nurses' Health Study. The women, ages 30 to 55, completed detailed questionnaires about their eating habits every four years from 1980 to 1994.
Researchers at the Harvard Medical School report that at the end of the period, 2,956 women had developed breast cancer. However, the researchers couldn't find any association between dietary fat and the fact that these women got breast cancer.
Breast cancer was found to be no more common among women who ate lots of fat, or among those who ate a large proportion of animal fat, polyunsaturated fat (vegetable fat) or trans-unsaturated fat (partially hydrogenated oils, such as those used in margarine and to cook doughnuts and french fries).
Nor was breast cancer any less common in women who got a high proportion of their fats from fish oil (previously believed to offer some protection from breast cancer) or less common in those women who got less than 20 percent of their total calories from fat.
Most surprisingly, women who ate the least fat appeared to have a 15 percent higher rate of breast cancer, the researchers said.
However, researchers were quick to point out that a low-fat diet is still an important factor in weight control, diabetes and heart disease, which is the No. 1 killer of women, not breast cancer.
To help prevent breast cancer, doctors still suggest that women avoid weight gain, especially after the age of 18, and limit alcohol consumption.