By DANIEL MARTIN

Last updated at 08:33 03 December 2007

Folklore holds that what mothers eat is the key to the sex of their child.

Red meat and salty snacks are said to lead to boys while chocolate is thought to help to produce girls.

Now science suggests the stories may be true: mice with low blood-sugar levels - a good indicator of a sugar-rich diet - produce more female than male offspring.

Researchers gave 20 female mice a steroid, dexamethasone, which kept their blood-sugar levels low.

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The sex of their litters was then compared with that of 20 mice on a regular diet.

Those eating normally produced offspring that were 53 per cent male. But those on the steroid produced litters that were only 41 per cent male.

The results showed that, in mice at least, a diet that is high in sugar can lead to more female offspring.

The scientists who carried out the research at the University of Pretoria in South Africa say the same could be true in humans.

But Elissa Cameron, who led the project, said it was unclear how blood-sugar levels affect the sex of the offspring.

Sex is determined by a chromosome contained in the sperm - X for a girl and Y for a boy. Women have two X chromosones.

But diet, in men, can have an impact by altering the proportion of sperm carrying X and Y chromosomes.

The latest research suggests food may affect the environment in the womb, creating conditions which are more favourable to male or female sperm.

Professor Cameron said her work raised the possibility that diet can influence the proportion of males and females in a population.

She said it also offered a possible answer to a key question in evolutionary theory - understanding the mechanisms through which animals 'select' the sex off their offspring.

Other studies have shown that the time of year a baby is conceived can have an impact on its sex.

In women, different types of food are suspected of increasing the chance of a miscarriage.