A team from Nottingham University studied the impact of diet of pregnant women on the gender of their child.

They found that while the national average in Britain is 106 boys born to every 100 girls, for vegetarian mothers the ratio was just 85 boys to 100 girls.

Researcher Pauline Hudson told BBC News Online that the findings of the study were statistically significant.

"This was an incidental finding - we had been looking at the impact of diet on baby weight - but it is not something we have published lightly, this was a very well carried out study."

Ms Hudson said the mechanism behind the impact of diet was unclear, but she put forward three possible theories:

• a vegetarian diet places stress on the female body, meaning that female foetuses, which are known to be more robust, survive, while male foetuses are killed off
• a vegetarian diet changes the acidity of the vaginal secretions, creating a hostile environment for sperm carrying male genetic information
• the diet contains chemicals which mimic the action of female sex hormones such as oestrogen

The research was dismissed by Catherine Collins, of the British Dietetic Association, as a "statistical fluke".