Hearty-Eating Moms More Likely to Have Boys

Previous research has shown -- despite the rising epidemic in obesity -- a reduction in the average energy uptake in advanced economies. The number of adults who skip breakfast has also increased substantially.

"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.

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 favorable -- 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 fertilization research that higher levels of glucose, or sugar, encourage the growth and development of male embryos while inhibiting female embryos.

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