What a pregnant woman was eating around the time of conception could influence whether her child is a girl or a boy, according to new research.
Women with the highest energy intake before pregnancy were more likely to have a boy than women with the lowest caloric intake (56% versus 45%), report study authors Fiona Mathews, D.Phil., of the University of Exeter in the UK, and colleagues in the April 2008 issue of the Proceedings of the Royal Society.
"Determining whether infant sex is 'naturally' influenced by maternal conditions is of direct relevance to the current debate about the artificial selection of the sex of an embryo during fertility treatment and in commercial 'gender clinics',"
Interestingly, what mothers eat during pregnancy seems to have no connection to the sex of the baby.
"Determining whether infant sex is 'naturally' influenced by maternal conditions is of direct relevance to the current debate about the artificial selection of the sex of an embryo during fertility treatment and in commercial 'gender clinics'," they added.
Other studies have shown that horses and other animals produce more sons when the mother has a rich diet. The researchers explain this in terms of an evolutionary drive to produce descendants, because "sons are more costly to produce in both the short and long terms than daughters," but can produce more offspring in the long term.
The study looked at 740 women who were pregnant for the first time and who had no medical problems, including obesity.
These women kept food diaries in early pregnancy and retrospectively reported their usual diet in the year before conception.
The researchers found that maternal diets high in nutrients, including protein, fat, vitamin C, folate, and minerals, were linked to children's sex before conception, whereas diets in early and late pregnancy were not.
Women with the highest energy intake before conception were 1.5 times more likely to have a boy than those with the lowest energy intake.
Among the individual food items reported on the food frequency questionnaires, breakfast cereal intake before pregnancy was the only one strongly associated with infant sex.
Women who ate more than one bowl of cereal a week were 1.87 times more likely to have a boy than those who ate cereal once a week or less.
One potential actor in this is glucose, which has been seen to favor growth and development of males while inhibiting that of females, they said. "Skipping breakfast extends the normal period of nocturnal fasting, depresses circulating glucose levels and may be interpreted by the body as indicative of poor environmental conditions."
Because all of the women in the study were white and had never been pregnant before, any possible influence of race and birth order, both of which are known to affect sex ratio, was avoided.