Trans fats, which have no nutritional value, are regularly added to thousands of processed foods in order to extend their shelf life. Studies have previously shown they increase the body's ratio of "bad" (LDL) to "good" (HDL) cholesterol, thus raising the risk of heart disease.
"There is already an overwhelming scientific case for banning trans fats," said Oliver Tickell of the anti-trans-fat group TFX, "and this new evidence gives it considerable new weight and urgency."
Researchers found that women who received 2 percent of their daily calories from trans fats -- as opposed to carbohydrates or other unsaturated fats -- were 70 to 100 percent more likely to suffer infertility due to lack of ovulation. For someone with a 2,000 calorie diet, this level of intake could be achieved by consuming just 4 grams of trans fats a day, an amount that could be found in a single doughnut or portion of french fries.
"It's really a small amount of fats that we observed having a significant effect on infertility," said lead researcher Dr. Jorge Chavarro.
While U.S. law requires that the trans fat content of foods be labeled, even careful consumers might still find themselves unknowingly eating 4 grams or more a day. By law, foods containing less than half a gram of trans fats per serving may be labeled as trans fat free.
"Food companies are knowingly hiding trans fats in processed foods by using small serving sizes combined with the 0.5 grams ... loophole," said Mike Adams, author of "Poison In the Food: Hydrogenated Oils."
"The labels claim the foods are trans fat free, but they may still contain considerable levels of the dangerous ingredient." He notes that besides looking at the nutrition facts labels, consumers should always check the ingredients list for "hydrogenated" or "partially hydrogenated" oils, and avoid products that contain either one.