When trans-fats were made for the first time, they were seen as the solution against artery clogging animal fats. Trans-fats or trans-fatty acids are made by solidifying oily fats by hydrogenization (adding hydrogen atoms into their molecule). Margarine was the best solution for replacing the harmful butter and lard. But now, after researches showed that trans-fats clog arteries just like the animal products, they also have been found to boost the risk of breast cancer, as signaled by a study carried out by a team led by Veronique Chajes of the French national scientific research centre at the University of Paris-South European, and published the in the American Journal of Epidemiology.

Women with the highest levels of trans-fats in the blood had a doubled risk of developing breast cancer, as compared with women displaying the lowest levels.
"At this stage, we can only recommend limiting the consumption of processed foods, the source of industrially produced trans-fatty acid," wrote the authors.

New York and California have already banned trans-fats in restaurant foods. In Canada and Britain, many food companies have renounced to their use. Trans-fats are common cooking fats in many countries, employed for making baked goods, snacks and prepared foods.

The subjects were part in a large European cancer trial. The team analyzed blood samples collected between 1995 and 1998 from 25 000 women, who also completed questionnaires about their eating and lifestyle habits. The subjects were followed up for years for the development of cancer.

363 of them got breast cancer. The higher levels of trans-fatty acids increased the probability of having cancer. Women with higher amounts of omega-3 fatty acids (abundant in fatty fish (like salmon), walnuts and leafy green vegetables), supposedly beneficial for the health, had the same risk of developing breast cancer. Obese women were the category most exposed to breast cancer (besides other types of cancer), and high-fat diets also boosted this risk.