Trans-fats not only clog arteries, but may also raise the risk of getting breast cancer.

Trans-fats are artificial by-products of the hydrogenation process of vegetable oils, developed by an inexpensive method. These were, ironically, meant to be healthful replacements for artery-clogging saturated fats such as butter and lard. But the process of making vegetable oil behave like butter made it as unhealthy as butter. Trans-fats can be found in cooking fats, baked goods, snacks and a variety of other prepared foods. Many countries in the West have banned trans-fats in restaurant foods.

To look into the adverse effects of trans-fats, French researchers looked at blood samples collected between 1995 and 1998 from 25,000 women who had volunteered to report on their eating and lifestyle habits and then be followed for years to see if they developed cancer. Out of these women, 363 were diagnosed with breast cancer. Their blood levels of fatty acids were compared with those of women without cancer. It was found that the higher the levels of trans-fatty acids, the more likely a woman was to have cancer. Women with higher levels of omega-3 fatty acids, being studied for their potential benefits to health, were not any less likely to have breast cancer. Obese women are more likely to develop breast cancer, among other types of cancer, and high-fat diets are also linked with breast cancer.

The findings suggest that people, especially women, should limit their consumption of processed foods, which is the source of industrially produced trans-fatty acid.