Besides causing heart disease, trans-fats were also discovered to increase the risk of developing breast cancer, new research revealed Friday.

Trans-fats are synthetic or artificial fats, which are converted from natural forms of vegetable oil through a chemical process called partial hydrogenation. They are widely used in processed foods to give a food unique texture and flavor and long shelf life. Also, trans-fats are widely present in processed food and foods served at restaurants.

Veronique Chajes of the French national scientific research center at the University of Paris-South and colleagues 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 to be followed for years to see if they developed cancer.

During the follow-up, 363 women were diagnosed with breast cancer. The researchers discovered that these women tended to have higher levels of trans-fats in their blood. To be more exact, the higher the levels of trans-fatty acids, the more likely the women were to have cancer, Chajes said.

Surprisingly, the study also found no decreased risk of breast cancer in women who had high levels of omega-3 fatty acids, which are believed to give health benefits.

"At this stage, we can only recommend limiting the consumption of processed foods, the source of industrially produced trans-fatty acid," the researchers said in their study.

New York and California have banned trans-fats in restaurant foods and Canada and Britain are considering following suit; many food companies have eliminated them from their products.

Breast cancer is the second most common cancer killer of women, after lung cancer. It will be diagnosed in 1.2 million people globally this year and will kill 500,000.

The findings of the study were published in the American Journal of Epidemiology.