Soy foods 'reduce sperm numbers' — or lesser men eat soy:
The Harvard School of Public Health study looked at the diets of 99 men who had attended a fertility clinic with their partners and provided a semen sample.
The men were divided into four groups depending on how much soy they ate, and when the sperm concentration of men eating the most soy was compared with those eating the least, there was a significant difference.
The “normal” sperm concentration for a man is between 80 and 120 million per millilitre, and the average of men who ate on average a portion of soy-based food every other day was 41 million fewer.
Dr Jorge Chavarro, who led the study, said that chemicals called isoflavones in the soy might be affecting sperm production.
These chemicals can have similar effects to the human hormone oestrogen.
Dr Chavarro noticed that overweight or obese men seemed even more prone to this effect, which may reflect the fact that higher levels of body fat can also lead to increased oestrogen production in men.