Trans Fats May Raise Risk of Infertility

Women who have trouble conceiving often endure costly and uncomfortable invasive procedures to bring egg and sperm together. For those having problems producing a monthly egg in the first place, a condition known as ovulatory infertility, there may be an easier solution—avoid the french fries, brownies, and oversized muffins.

Jorge Chavarro, Walter Willett, and colleagues found that women who consumed two percent of their daily calories in the form of trans fat—which translates to four grams of fat for a woman eating 1,800 calories a day—exhibited a 73 percent greater chance of developing ovulatory infertility than those who consumed those calories in the form of carbohydrates. When the trans fat–consuming women were compared to women who filled that two percent slot with omega-6 polyunsaturated fats, such as canola and corn oil, the relative risk went up to 79 percent. Compared to women eating even healthier monounsaturated fats such as olive oil, trans fat–eating women had a more than twofold risk of developing ovulatory infertility. The findings appear in the January American Journal of Clinical Nutrition.

“What would happen if instead of cooking or baking with trans fats you used a healthier oil—instead of frying with margarine, you used olive oil or corn oil?” asked Chavarro, research fellow in the Department of Nutrition at HSPH. “That is more or less what we were comparing here.”

The dangers of trans fats, which are formed when vegetable oils are converted into semisolid form, are well known and recently led the New York City board of health to ban their use in restaurants. Yet no one had looked for a link with infertility. Some studies had shown that women with polycystic ovarian syndrome, who often exhibit ovulatory infertility, had more ovulations and, in some cases, got pregnant when taking medicines that activate the peroxisome proliferator–activated receptor gamma (PPAR-gamma). Though fatty acids appear to be natural ligands for the receptor, trans-fat binding has been associated with inflammation and other deleterious effects.

Spurred by these findings, Chavarro, Willett, the Frederick John Stare professor of epidemiology and nutrition at HSPH, and colleagues turned to data from the Nurses’ Health Study II. Willett and colleagues began the study in 1989, registering 116,671 women between 24 and 42 years of age. The women are followed every other year and every four years are asked to fill out an extensive questionnaire about diet. Chavarro and colleagues decided to focus on 18,555 married women, each with no previous history of infertility, who between 1991 and 1999 either became pregnant or had problems conceiving. (Married women were chosen because their pregnancies and efforts to conceive are more likely intentional.) The latter group was divided into women who attributed their problem to skipped periods (ovulatory infertility) and those who gave other reasons. The researchers identified 438 women in the ovulatory infertile group and compared them to the other two groups—those who had become pregnant or reported infertility for other reasons. Taken as a group, the 438 women with ovulatory infertility reported consuming higher levels of trans fats, though the findings must be taken with a statistical grain of salt.

“That does not mean you will be infertile or that you’re not going to be able to have children if you eat trans fats, but it means that it is going to be much harder,” Chavarro said. And the risk of developing ovulatory infertility goes up another 73 percent for every additional four grams of fat an 1,800 calorie–consuming woman eats.

“Avoid trans fats. There is really no good reason to eat them,” said Chavarro.