Scientists at Oxford and Exeter universities asked 740 women, who had become pregnant for the first time, about their eating patterns in the year before they conceived. They then divided the women into high, medium and low calorie groups.

They found that 56 per cent of women in the high calorie group gave birth to boys, compared with 45 per cent in the lower calorie group. None of the women was obese or aware of the gender of her baby throughout her pregnancy.

“For the first time, we’ve shown there is a clear association between a mother's diet and the gender of her infant,” said Fiona Mathews, a specialist in mammalian biology at Exeter University, who led the research.
“The mother seems to be able to influence the survival of either the sperm or the fertilised egg in its very early stages, probably before it has even implanted in the womb.”

When the researchers looked more closely at the women's diets, they found that certain nutrients were key to the effect, she said.

“We were able to confirm the old wives’ tale that eating bananas and so having a high potassium intake was associated with having a boy, as was a high sodium intake. But the old tale about drinking a lot of milk to have a girl doesn’t seem to hold up. In fact, more calcium meant they were again more likely to have a boy.

Natural phenomena

The finding makes evolutionary sense and mirrors a similar effect seen in other animals. Females are more likely to be born when food is scarce, since they are more likely to produce at least some babies. Males are more of a gamble though, with some having lots of offspring and others having none.

While it might be possible for a woman to boost the effect by substantially changing her diet, scientists warned that consuming high levels of salt or dramatically altering levels of other nutrients could be harmful.