A new study suggests that a pregnant woman who eats more around the time her baby is conceived is more likely to give birth to a boy.
The research, a joint effort between the University of Exeter and Oxford University in England, is published in the journal Proceedings of the Royal Society B: Biological Sciences.
Researchers asked 740 pregnant, first-time mothers who did not know the sex of their baby about their eating habits before and during the early stages of their pregnancies. The women were then split into groups according to how many calories they consumed around the time their babies were conceived.
The study found that 56 per cent of the women in the group with the highest caloric intake at conception had boys, compared to 45 per cent in the group with the lowest energy intake.
The women who had sons were also more likely to have eaten a wider variety of nutrients, such as potassium, calcium and vitamins C, E and B12. Women who ate breakfast cereals were also more likely to have sons.
"That's my staple in the morning, warm cereal, oatmeal pretty well religiously every day," said Andrea Page, fitness instructor of Fit Moms in Toronto and a mother of three boys.
Because gender is genetically determined by fathers, the findings are interesting because they show that women can perhaps influence the development of one sex over another.
Fewer boys are being born in industrialized countries, such as the United Kingdon, the United States and Canada. At the same time, the average caloric intake in these countries has declined, and more people are skipping breakfast. In the U.S., for example, 75 per cent of adults reported eating breakfast in 1991, compared to 86 per cent in 1965.
"We know from other studies that if you skip breakfast, you end up with low blood sugar levels and I suggest it may be the low blood sugar that is then unfavourable to the survival of male embryos," said lead study author Fiona Mathews of the University of Exeter.
However, women are not advised to skip breakfast if they are hoping to have a girl. People who eat a healthy diet maintain a better body weight and have a better overall nutritional status, said dietician Jennifer Sygo.
"If you have someone wanting a girl and you skip breakfast and breakfast cereals, you could have nutritional consequences in the long run," said Sygo.
Scientists that study animal behavior have already noticed that in some species, females produce more sons when resources, such as food, are plentiful. This has mostly been seen in invertebrates, but also in horses, cows and some deer species.
There, this study's findings could indicate that when it isn't given enough food, a woman's body interprets that as a sign of low food availability.
Based on a report by CTV's medical correspondent Avis Favaro and producer Elizabeth St. Philip.
Abstract:
You are what your mother eats: evidence for maternal preconception diet influencing foetal sex in humans
Fiona Mathews, Paul J. Johnson and Andrew Neil
Facultative adjustment of sex ratios by mothers occurs in some animals, and has been linked to resource availability. In mammals, the search for consistent patterns is complicated by variations in mating systems, social hierarchies and litter sizes. Humans have low fecundity, high maternal investment and a potentially high differential between the numbers of offspring produced by sons and daughters: these conditions should favour the evolution of facultative sex ratio variation. Yet little is known of natural mechanisms of sex allocation in humans. Here, using data from 740 British women who were unaware of their foetus's Q4 gender, we show that foetal sex is associated with maternal diet at conception. In 56% of women, the highest third of preconceptional energy intake bore boys, compared with 45% in the lowest third. Intakes during pregnancy were not associated with sex, suggesting that the foetus does not manipulate maternal diet. Our results support hypotheses predicting investment in costly male offspring when resources are plentiful. Dietary changes may therefore explain the falling proportion of male births in industrialized countries. The results are relevant to the current debate about the artificial selection of offspring sex in fertility treatment and commercial 'gender clinics.'
