Trans Fats Linked to Infertility

March 22, 2007—Trans fats are linked to an increased risk of heart disease and possibly diabetes; now it appears that they also impair fertility, according to a study in the American Journal of Clinical Nutrition.

Trans fat is formed when hydrogen is added to a liquid fat, making it solid at room temperature. Small amounts of trans fats are found naturally in some animal foods like butter and meat, but most trans fat in the diet comes from partially hydrogenated vegetable oils like margarine or shortening. Because these fats have a longer shelf life and can be heated to high temperatures, they’re commonly used in processed foods like crackers, candies, cookies, fried foods, and baked goods. Trans fats raise levels of LDL (“bad”) cholesterol and lower levels of heart-protective HDL cholesterol, increasing risk of heart disease. They cause blood platelets to stick together, increasing the chance of forming a dangerous blood clot. Trans fats increase inflammation in the body, which could further explain their role in increasing heart disease and stroke risk, and could also link them to diabetes and other chronic diseases.

Infertility affects between 10 and 15% of couples. “We decided to test the hypothesis that trans fatty acids increase the risk of ovulatory infertility,” said researchers from Harvard Medical School. Ovulatory infertility is the inability to become pregnant after 12 months of unprotected intercourse that is caused by a problem related to ovulation.

During the eight-year study, 18,555 women provided information about their dietary habits and pregnancies as part of the Nurses Health Study II. While trying to become pregnant, 438 women were diagnosed with ovulatory infertility.

The researchers found that consuming trans fats was tied to infertility. When women replaced 2% of their calories from carbohydrates or omega-6 polyunsaturated fats with trans fats, their risk of ovulatory infertility increased by 73% and 79%, respectively; replacing monounsaturated fats with trans fats more than doubled the risk.

The results of this study confirm what we already know: artificially produced trans fats have no place in the human diet and have the potential to cause disease. The FDA estimates that the average American gets about 3% of their total daily calories from trans fats. Replacing trans fats with mono and polyunsaturated fats from sources like olive, sesame, and safflower oils could be a simple way to enhance fertility.

“Because replacing trans fats with nonhydrogenated vegetable oils is likely to reduce the risk of coronary heart disease and type 2 diabetes, women planning to become pregnant should consider this strategy; it could reduce their risk of infertility, as well,” the team concluded.

(Am J Clin Nutr 2007;85:231–7)

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Kimberly Beauchamp, ND, earned her bachelor’s degree from the University of Rhode Island and her Doctorate of Naturopathic Medicine from Bastyr University in Kenmore, WA. She cofounded South County Naturopaths in Wakefield, RI. Dr. Beauchamp practices as a birth doula and lectures on topics including whole-foods nutrition, detoxification, and women’s health.

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