Trans-fatty acids have been banned from many cities and states because they increase the risk of heart disease.
Now, French researchers have found that women with the highest levels of trans-fats had about twice the risk of breast cancer. Scientists looked at blood samples of 25,000 women taken from 1995 to 1998. They then studied more than 360 of the women who were diagnosed with breast cancer.
The study is in the American Journal of Epidemiology.