Soy protein isolates of varying isoflavone content do not adversely affect semen quality in healthy young men

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.