The studies on this appear very contradictory. These were the only human studies I found on Medline on the subject. The one study that shows a possible link to low sperm counts also states that this was in overweight and obese men. Keep in mind that fat cells generate estrogen, which is not only hundreds of times stronger than phytoestrogens but can also lower sperm counts.
The phytoestrogen causes lowered sperm counts is also bogus in my mind due to the fact that nearly all fruits and vegetables we eat contain phytoestrogens or bioflavonoids that function like phytoestrogens. Therefore if phytoestrogens reduced sperm counts then most of us would not exist.
Department of Genetic Medicine and Development, University of Geneva Medical School, Geneva, Switzerland.
There is growing interest in the possible health threat posed by the effects of endocrine disruptors on reproduction. Soy and soy-derived products contain isoflavones that mimic the actions of oestrogens and may exert adverse effects on male fertility. The purpose of this review was to examine the evidence regarding the potential detrimental effects of soy and phyto-oestrogens on male reproductive function and fertility in humans and animals. Overall, there are some indications that phyto-oestrogens, alone or in combination with other endocrine disruptors, may alter reproductive hormones, spermatogenesis, sperm capacitation and fertility. However, these results must be interpreted with care, as a result of the paucity of human studies and as numerous reports did not reveal any adverse effects on male reproductive physiology. Further investigation is needed before a firm conclusion can be drawn. In the meantime, caution would suggest that perinatal phyto-oestrogen exposure, such as that found in infants feeding on soy-based formula, should be avoided.
Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, Canada.
OBJECTIVE: To determine the effects of consumption of soy protein of varying isoflavone content on parameters of semen quality in healthy young men. DESIGN: Randomized crossover intervention. SETTING: University campus. PATIENT(S): Healthy adult men (age 27.5+/-5.67 years, body mass index 25.4+/-3.14 kg/m(2)). INTERVENTION(S): Milk protein isolate (MPI), low-isoflavone soy protein isolate (low-iso SPI; 1.64+/-0.19 mg isoflavones/day, expressed as aglycone equivalents), and high-isoflavone soy protein isolate (high-iso SPI; 61.7+/-7.35 mg isoflavones/day, expressed as aglycone equivalents) for 57 days each separated by 28-day washout periods. MAIN OUTCOME MEASURE(S): Urinary isoflavones were measured from 24-hour urine samples collected on days 54-56 of each treatment period. Semen quality parameters (semen volume, sperm concentration, sperm count, sperm percent motility, total motile sperm count, sperm morphology) were measured from semen samples collected on days 1 and 57 of each treatment period. RESULT(S): Urinary isoflavones were significantly higher after consumption of high-iso SPI compared with the low-iso SPI and MPI. Semen parameters, including semen volume, sperm concentration, sperm count, sperm percent motility, total motile sperm count, and sperm morphology, were not significantly affected by consumption of either low- or high-iso SPI compared with MPI. CONCLUSION(S): Consumption of soy protein of low or high isoflavone content does not adversely affect semen quality in a sample of healthy adult men.
Department of Nutrition, Harvard School of Public Health, Boston, MA, USA. firstname.lastname@example.org
BACKGROUND: High isoflavone intake has been related to decreased fertility in animal studies, but data in humans are scarce. Thus, we examined the association of soy foods and isoflavones intake with semen quality parameters. METHODS: The intake of 15 soy-based foods in the previous 3 months was assessed for 99 male partners of subfertile couples who presented for semen analyses to the Massachusetts General Hospital Fertility Center. Linear and quantile regression were used to determine the association of soy foods and isoflavones intake with semen quality parameters while adjusting for personal characteristics. RESULTS: There was an inverse association between soy food intake and sperm concentration that remained significant after accounting for age, abstinence time, body mass index, caffeine and alcohol intake and smoking. In the multivariate-adjusted analyses, men in the highest category of soy food intake had 41 million sperm/ml less than men who did not consume soy foods (95% confidence interval = -74, -8; P, trend = 0.02). Results for individual soy isoflavones were similar to the results for soy foods and were strongest for glycitein, but did not reach statistical significance. The inverse relation between soy food intake and sperm concentration was more pronounced in the high end of the distribution (90th and 75th percentile) and among overweight or obese men. Soy food and soy isoflavone intake were unrelated to sperm motility, sperm morphology or ejaculate volume. CONCLUSIONS: These data suggest that higher intake of soy foods and soy isoflavones is associated with lower sperm concentration.