Today not much is known on diet factors influencing human fertility, however a recent study suggests that trans fats increase a woman's risk of infertility [1]. More than 7 million women in the United States have difficulties to get pregnant. This accounts to almost 15% of couples, and the problem is still growing [2]. That situation fuels assisted reproduction technologies to be a blooming business in recent years. Unfortunately, such procedures are too expensive for too many to deal with infertility at a population level. It would be important thus to identify definite risk factors to be able to prevent infertility.

Some forms of infertility were previously suggested to be connected to factors increasing insulin resistance, with obesity and low physical activity being the most important. Notably, pharmacological compounds restoring body sensitivity to insulin resulted in trials in a better ovulatory function in women with polycystic ovary syndrome [3]. The compounds worked by activation of an important cellular protein factors named peroxisome proliferator–activated receptors (PPARs), known to be regulators of lipid metabolism. Interestingly, trans unsaturated fatty acids (trans fats) have been found to interact with PPARs [4].

Trans fats can be found in vegetable shortenings, some margarines, crackers, cookies, snack foods, and other foods. Unlike other fats, the majority of trans fats are formed when food manufacturers turn liquid oils into solid fats like shortening and hard margarine by adding hydrogen to vegetable oil in a process called hydrogenation. Hydrogenation increases the shelf life and flavor stability of foods containing these fats. A small amount of trans fat is found naturally, primarily in some animal-based foods, however trans fats from partially hydrogenated oils are generally considered to be more of a health risk than those occurring naturally [5]. Eating trans fat was associated with increased risk of coronary heart disease [6], insulin resistance and risk of type 2 diabetes [7]. Thanks to a greater public awareness of the health risks associated with trans fats many companies are voluntarily removing trans fats from their products, or establishing trans-free product lines. Notably, recently New York City banned use of trans fats in restaurants. Chicago officials are said to be considering a similar move. Also, chains as Wendy’s, Chili’s, KFC, Taco Bell, and Starbucks all recently announced they would eliminate or greatly reduce the amount of trans fats in their products. These are very good examples and hopefully many more will follow.

Recently, inspired by the trans fats and PPARs association, researchers from the Harvard School of Public Health decided to test the hypothesis that trans fats increase the risk of ovulation related infertility. Based on data from The Nurses' Health Study II (a big prospective investigation into the risk factors for major chronic diseases in women based on female registered nurses), the researchers analyzed 18 555 women without a history of infertility who tried to become pregnant or became pregnant between 1991 and 1999 [1]. A total of 438 women were diagnosed with ovulation-related infertility during that eight-year period.

The study found that obtaining just 2% of total calories from trans fats instead of monounsaturated fats doubled the risk for ovulation related infertility. That’s translates to only 4 grams of trans fats for a woman eating 1,800 calories per day. Additionally, after adjusting for other known and suspected infertility risk factors, the data shown that each 2% increase in trans fat consumption as a replacement for carbohydrates resulted in a 73% greater risk of ovulation related infertility, Interestingly, only the trans fats were found to have a negative impact on ovulation related fertility as neither total fat intake nor total cholesterol intake was found to be associated with that type of infertility.

The results of that study may constitute a very important observation and they may have a great impact on our understanding and future approaches to infertility. However, there are some limitations of such type of studies, in big part based on statistical analysis with numerous adjustments. Indeed, other independent nutritional researchers are skeptical about the Harvard trans fat and fertility study conclusions. Looking into raw data of the study before statistical adjustments, the association of trans fats with infertility is not so obvious. Importantly, the women groups analyzed in this study differed in several other important characteristics then only the fat intake. As compared with women with lower total fat intake, women with a higher intake of total fat were younger and consumed less alcohol, they also were heavier, less physically active, more likely to smoke, and more likely to report use of oral contraception at the beginning of the study [1]. Moreover, women with higher fat intake were less likely to use multiple vitamin supplements and more frequently have never given birth, than were those with lower fat intake[1]. All these are important factors which may significantly influence the infertility rates. Another important limitation of the study is the fact that not all of the women involved were planning to become pregnant. As the authors point themselves, cases who were clearly attempting to conceive, may have been more health-conscious than the pregnancy non-cases, who may have conceived accidentally.

In summary, we have to realize that findings of such magnitude as the described study on trans fats in relation to infertility could clearly get high publicity, and in turn may strongly influence the interested population. Even if the arguments represented in the recent study may not be compelling, in this case it is still a very good idea to stay away form trans fats, and it is not only for women planning pregnancies but for the whole society. There are many good reasons for that, and the future may show if infertility is really one of them.

References:

1. Chavarro J. E., Rich-Edwards J. W., Rosner B. A., Willett W. C. (2007). Dietary fatty acid intakes and the risk of ovulatory infertility. American Journal of Clinical Nutrition, vol 85, pp 231-237.

2. Chandra A., Martinez G.M., Mosher W.D., Abma J.C., Jones J. (2005). Fertility, family planning, and reproductive health of U.S. women: data from the 2002 National Survey of Family Growth. Vital Health Stat. vol. 25, pp. 1–160.

3. Cataldo N.A., Abbasi F., McLaughlin T.L., et al. (2006). Metabolic and ovarian effects of rosiglitazone treatment for 12 weeks in insulin-resistant women with polycystic ovary syndrome. Hum Reproduction. Vol. 21 pp.109–120.

4. Berger J., Moller D.E. (2002). The mechanism of action of PPARs. Annu Rev Med, vol. 53, pp. 409–435.

5. Mozaffarian D., Katan M.B., Ascherio A., Stampfer M.J., Willett W.C. (2006). Trans Fatty Acids and Cardiovascular Disease. New England Journal of Medicine, vol. 354 (15), pp. 1601-1613.

6. Food and nutrition board, institute of medicine of the national academies (2005). Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids (Macronutrients). National Academies Press, 504.

7. Salmeron J., Hu F.B., Manson J.E., et al. (2001). Dietary fat intake and risk of type 2 diabetes in women. Am J Clin Nutr, vol. 73, pp.1019–1026.

B. A. Kwiatkowski, Ph.D. has been involved in biomedical research for over two decades and published several peer reviewed scientific articles in top biomedical journals. Recently he also writes popular health and medical research articles for BioMedClub (http://www.biomedclub.com). You can find more information about trans fats and infertility studies and read about other health issues at: http://www.biomedclub.com/articles/

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