A legion of old wives says 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. Those biddies may be onto something.

Biologist Elissa Cameron at the University of Pretoria in South Africa seems to think so too. She and her research team altered the blood sugar levels of laboratory mice before mating and found that more females were born to mice with lower blood sugar levels.

The scientists gave 20 female mice water dosed with a steroid that inhibits the absorption of glucose for three days while they were exposed to males for mating. 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.

Exactly how a drop in blood sugar would cause more female births is still a mystery, but the opposite also seems to support the findings. A previous study using diabetic mice, found that rodents with high blood-sugar levels produced more male offspring than expected.

Cameron says the old wives' tales are based on the same science, "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."