If your client is trying to conceive, I can almost guarantee you that one of the first questions out of her mouth will be, “How does soy affect my fertility?”
Rest assured; this isn’t a topic we covered in school, from what I can remember, so you’re not alone if you’re not quite sure how to answer this.
Dietitians know how important it is to evaluate the longitudinal research behind a topic before making a decision one way or another. Plus, as we know from trends of the past, what’s right for one person may not always be right for another. So, let’s proceed with caution as we look at the facts presented through the scientific literature.
As a member of the American Society for Reproductive Medicine, I spend my afternoons reading the latest research on fertility, assisted reproductive technology, (ART) and all things baby.
One of the most significant longitudinal studies referenced throughout fertility research is the Nurses’ Health Study II (NHS II). Researchers collected data on the diets and lifestyles of more than 116,000 female nurses between the ages of 25 and 42 to evaluate their corresponding risk of chronic diseases.1 Analyses of conception rates in a subset of these women revealed that higher intake of animal protein increased the likelihood of ovulatory infertility. Researchers concluded that adding one serving of beans, peas, nuts, peanuts, tofu, and soybeans may protect against ovulatory infertility.1-3
A smaller study suggests that a diet rich in soyfoods may be beneficial for women undergoing assisted reproductive therapy. Fertilization rates, clinical pregnancies, and live births were all higher among women who consumed more soyfoods. The research also suggests that isoflavones play a role, but the mechanism of action is unclear.4
Other research points to the fact that soyfoods may have less of an impact on insulin release than animal protein.1,2 Excess insulin in the bloodstream has been linked to ovulation problems, including hormonal disruption.1,2
Research also has been conducted on the impact of diet on male fertility. A 2010 review found that current data available from nine clinical studies showed that soy isoflavone exposure doesn’t affect circulating estrogen levels in men. Though the three intervention studies reviewed were limited in length, they showed that soy isoflavones don’t affect sperm or semen parameters.5
A 2010 randomized crossover intervention trial investigated the effect of soy isoflavones on semen quality in 32 healthy young adult men. Participants consumed milk protein isolate, low-isoflavone soy protein isolate, and high-isoflavone soy protein isolate, and urine and semen samples were collected to evaluate the effect of the treatments on each. Results found that in healthy adult men, the level of isoflavones in soy protein doesn’t affect semen quality.6
Though there’s certainly more research on the horizon in this area of fertility and nutrition, the research currently available suggests that moderate soy intake can be included as part of a healthful diet while trying to conceive and may be protective against ovulatory infertility.
— Elizabeth Shaw, MS, RDN, CLT, is a nutrition communications consultant and adjunct professor of nutrition in San Diego, California. She’s the recipe creator behind the popular blog ShawSimpleSwaps.com, freelance writer for Shape and Fitness magazines, and coauthor of Fueling Fertility.
- Nurses’ Health Study website. http://www.nurseshealthstudy.org/. Accessed February 27, 2017.
- Chavarro JE, Willett WC, Skerrett PJ. The Fertility Diet: Groundbreaking Research Reveals Natural Ways to Boost Ovulation & Improve Your Chances of Getting Pregnant. New York, NY: McGraw-Hill; 2008.
- Chavarro JE, Rich-Edwards JW, Rosner BA, Willett WC. Diet and lifestyle in the prevention of ovulatory disorder infertility. Obstet Gynecol. 2007;110(5):1050-
- Vanegas JC, Afeiche MC, Gaskins AJ, et al. Soy food intake and treatment outcomes of women undergoing assisted reproductive technology. Fertil Steril. 2015;103(3):749-755.e2.
- Messina M. Soybean isoflavone exposure does not have feminizing effects on men: a critical examination of the clinical evidence. Fertil Steril. 2010;93(7):2095-2104.
- Beaton LK, McVeigh BL, Dillingham BL, Lampe JW, Duncan AM. Soy protein isolates of varying isoflavone content do not adversely affect semen quality in healthy young men. Fertil Stertil. 2010;94(5):1717-1722.