Previous studies had found a correlation between soy and male fertility in animal research, but researchers from Harvard School of Public Health have finally confirmed the same thing is happening in humans.
They monitored the diets of 99 males who were attending the Massachusetts General Hospital Fertility Center. Over a three-month period, the men ate 15 soy-based foods and their semen quality was assessed.
The researchers found an inverse association between the amount of soy food and isoflavones consumed and the quality of the men's sperm; in other words, the men who ate the most soy had the lowest sperm quality, and this remained true even after allowing for weight, smoking, alcohol and caffeine consumption.
(Source: Human Reproduction, 2008; published online, July 23; doi: 10.1093/humrep/den243).