Male factor etiology may be a contributing factor in up to 60% of infertility cases. Clinical studies show that neither soyfood nor isoflavone intake affects sperm or semen parameters. However, a pilot epidemiologic study from the Harvard University School of Public published in 2008 found that soy intake was associated with low sperm concentration although not sperm count. That epidemiologic study had quite a few weaknesses but it received considerable attention nonetheless. In contrast to those results, the current study found that high soy intake by the male partners of couples undergoing fertility treatment with in vitro fertilization was unrelated to unrelated to fertilization rates, the proportions of poor quality embryos, accelerated or slow embryo cleavage rate, and implantation, clinical pregnancy and live birth. A total of 182 men participated in this study.
Although the results from Western epidemiologic studies involving the general population are usually of questionable value because of the generally low soy intake, in this study mean isoflavone intake in the highest intake group, which was comprised of 33 men, was 24 mg/day, an amount equivalent to approximately one serving per day and more than twice the isoflavone intake in the aforementioned 2008 study. The results of this in vitro fertilization study when combined with the results of clinical studies should resolve the issue of whether soy intake impairs male fertility.
Minguez-Alarcon L, Afeiche MC, Chiu YH, et al. Male soy food intake was not associated with in vitro fertilization outcomes among couples attending a fertility center. Andrology. (2015).