A US study recently found a potential negative link between soy food intake and sperm concentration, as we reported in BioNews last week. But now soy producers around the world have disputed the findings, and are calling for more research in the area.
The study, published last week in the journal Human Reproduction, looked retrospectively at soy foods intake and sperm count in a group of men. Dr Jorge Chavarro led the study at the Harvard School of Public Health in Boston, US. A negative association was found between soy in the diet and sperm concentration after accounting for factors such as age, BMI (body mass index), caffeine and alcohol intake, smoking and abstinence time. The researchers claim that the results could be due to the isoflavone content of soy, which could interfere with hormone signals in the body. It was also noted that the effect was more pronounced in overweight men.
However, according to the chair of UK group the Soya Protein Association Nigel Duffin in a letter to the Guardian newspaper, the study is 'incomplete and does not tell the full story'. He says that the study did not take into account other factors such as other foods, medications, sexual activities or environmental factors which may have affected sperm concentration, and also that there was no negative correlation found between soy foods and sperm mobility and quality, which both play a role in fertility. He suggested that 'obesity may be the explanation'.
Duffin also said: 'generations of Asians have regularly consumed soya without fertility disorders, and Asian countries have prodigiously produced very healthy, highly functioning children for centuries'.
Professor Richard Ivell, from the University of Adelaide, Australia, also said that the study is 'weak' and that 'studies with more money and bigger designs' were required. The US group the Soyfoods Association of North America also refute the findings, saying that the study 'conflicts with the large body of US government and National Institutes of Health-sponsored human and primate research'.