A new study on mice has revealed that a child's gender could be influenced by the mother's diet in the run-up to conception.
The study, by researchers at the University of Pretoria in South Africa, showed that mice given drugs to lower their blood-sugar levels produced considerably more female than male offspring.
According to lead author Elissa Cameron, the findings lend credibility to conventional beliefs that eating certain foods can influence the sex of offspring.
The traditional view holds that the father's sperm is the main determinant of the sex of a child. However, more and more scientists have found hints that maternal factors might play a part too.
Cameron and her colleagues wanted to examine how changes in diet might influence sex ratios i.e. the proportion of males to females in a population.
For this, they changed the levels of blood sugar in female mice during conception, by feeding the mice a steroid called dexamethasone (DEX), which restrains the transport of glucose into the bloodstream.
The scientists gave 20 female mice water dosed with DEX for the first three days that the females were exposed to males. Afterwards, the mice were given plain water.
Cameron's team measured the blood-sugar levels of these mice, as well as that of 20 control females several times during the experiment.
The average blood-glucose levels in mice that received DEX dropped from 6.47 to 5.24 millimoles/litre.
The team discovered that 53 percent of the pups born to the control female mice were male, but only 41 percent of those born to the mice receiving DEX were male.
Exactly how a drop in blood sugar causes more female births remains ambiguous, according to researchers.
The belief of diet influencing sex ratio is already part of conventional knowledge. According to folklore, mothers should eat more red meat and salty snacks if they want a boy, and fish, vegetables, chocolates and sweets if they want a girl.
"This is interesting, since meat raises blood sugar for a sustained period of time, whereas sugar-based snacks raise blood sugar very high, but for a short amount of time, followed by a slump in blood glucose," NewScientist.com quoted Cameron, as saying.
The study is published in the Proceedings of the Royal Society B.