Sex determination: Calorie intake has been linked to gender in human embryos. The image shows a 3-D ultrasound image of a 21-week old foetus.

Credit: iStockphoto

Related articles

• Women prefer men desired by others
• Women have always outlived men
• Sex wars fought with spiky genitals
• Sex on the brain? No, in the nose
• Crowds cause sex change

PARIS: Oysters may excite the libido, but there is nothing like a hearty breakfast laced with sugar to boost a woman's chances of conceiving a son, according to a study released today.

Likewise, a low-energy diet that skimps on calories, minerals and nutrients is more likely to yield a female of the human species, says the study, published in the U.K. journal, the Proceedings of the Royal Society B.

Impact on gender

Fiona Mathews of the University of Exeter in England and her team wanted to find out if a woman's diet has an impact on the gender of her offspring.

So they asked 740 first-time mothers who did not know if their unborn foetuses were male or female to provide detailed records of eating habits before and after they became pregnant. The women were split into three groups according to the number calories they consumed per day around the time of conception.

Fifty-six percent of the women in the group with the highest energy intake had sons, compared to 45 per cent in the least-well fed cohort.

Beside racking up a higher calorie count, the group who produced more males were also more likely to have eaten a wider range of nutrients, including potassium, calcium and vitamins C, E and B12.

Surprise findings

The odds of an XY, or male outcome to a pregnancy also went up sharply "for women who consumed at least one bowl of breakfast cereal daily compared with those who ate less than or equal to one bowl of week," the study reported.

These surprising findings are consistent with a very gradual shift in favour of girls over the last four decades in the sex ratio of newborns, according to the researchers.

Previous research has shown a reduction in the average energy uptake in advanced economies since the mid-1900s. The number of adults who skip breakfast has also increased substantially.

Though this seemingly conflicts with the rising epidemic in obesity, the explanation is that most people are doing less physical activity than people half a century ago.

"This research may help to explain why in developed countries, where many young women choose low calorie diets, the proportion of boys is falling," Mathews said.
The study's findings, she added, could point to a "natural mechanism" for gender selection.

Evolutionary perspective

The link between a rich diet and male children may have an evolutionary explanation.

For most species, the number of offspring a male can father exceeds the number a female can give birth to. But only if conditions are favourable – poor quality male specimens may fail to breed at all, whereas females reproduce more consistently.

"If a mother has plentiful resources, then it can make sense to invest in producing a son because he is likely to produce more grandchildren than would a daughter," thus contributing to the survival of the species, explains Mathews.

"However, in leaner times having a daughter is a safer bet."

While the mechanism is not yet understood, it is known from in vitro fertilisation (IVF) research that higher levels of glucose, or sugar, encourage the growth and development of male embryos while inhibiting female embryos.