Too much tofu may affect a man's fertility, according to a study linking soya and low sperm count.
Scientists found that even modest consumption of soya products, such as meat and dairy substitutes and bean curd, could have a significant impact on sperm count.
Men who ate an average of half a serving of soya food a day had lower concentrations of sperm than those who did not.
Low sperm count is known to make it harder for a couple to conceive.
Soya compounds called isoflavones, which mimic the female sex hormone oestrogen, are thought to be behind the effect.
Animal studies have linked high consumption of isoflavones with infertility. However, until now, there has been little evidence of their impact on human reproduction.
The scientists, led by Dr Jorge Chavarro from the Harvard School of Public Health in Boston in the US, questioned 99 men seeking help for fertility problems about their consumption of 15 soya-based foods for their study.