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Eating soy 'reduces sperm quality'

24/07/2008

Men who eat soy foods are more likely to have lower concentrations of sperm, a new study claimed today.

The link between soy and sperm quality was found to be particularly marked in men who were overweight or obese.

Researchers at the Harvard School of Public Health made the discovery after studying the relationship between semen quality and isoflavones - plant compounds that can behave like the hormone oestrogen and are mainly found in soy beans and soy-derived products.

They analysed the intake of 15 soy-based foods in 99 men who attended a fertility clinic with their partners to be evaluated for fertility problems between 2000 and 2006.

They asked them how often and how much they had eaten in the previous three months.

The foods included tofu, tempeh, tofu or soy sausages, bacon, burgers and mince, soy milk, cheese, yoghurt and ice cream, and other soy products such as roasted nuts, drinks, powders and energy bars.

After adjusting for factors such as age, abstinence time, body mass index, alcohol and caffeine intake and smoking, the researchers found that men in the highest intake category had, on average, 41 million sperm/ml less than men who did not eat soy foods.

The 'normal' sperm concentration for men ranges between 80-120 million/ml.

They also found the relationship between soy foods and sperm concentration was strongest in men with the higher sperm concentrations.

"The implication is that men who have normal or high sperm counts may be more susceptible to soy foods than men with low sperm counts, but this remains to be evaluated," explained researcher Dr Jorge Chavarro.

The study did not reveal why soy foods have this effect on sperm, but the researchers argue that increased oestrogen activity may have an adverse effect on the production of sperm by interfering with other hormonal signals.

This effect could be strengthened further in overweight and obese men because men with high levels of body fat produce more oestrogen than slimmer men, leading to high overall levels of oestrogen in the body and reproductive organs.

The research is published in the journal Human Reproduction.