Women who ate more total calories also delivered more boys, even though the
overall male-to-female birth ratio among the study participants was close to
The early findings in no way prove that what a woman does or doesn't eat
prior to conception influences her baby's sex.
But they do hint at a sex-selection bias among humans similar to that seen
in other animals, favoring male births among well-fed mothers and female births
among mothers who are less well nourished.
They may also help explain a subtle decline in the proportion of male births
in industrialized countries like the U.S., researcher Fiona Mathews, PhD, tells
"It is true that there is an obesity epidemic, but there is also an increase in dieting and very unstable dietary habits among young
women," she says. "And more people are skipping breakfast. Our
data suggest that these things may play a role in the small but noticeable
decline in male births."
The study involved 740 newly pregnant British women who had not given birth
before and who did not know the sex of their fetuses. All the women were white,
non-obese, and had no medical problems.
The women completed detailed food-frequency questionnaires during the first
pregnancy exam and well into their pregnancy, and they were asked to keep a
detailed food journal for a week around the time of their fourth month of
They were also asked to recall their dietary habits in the year prior to
Using this data, the researchers determined that women who ate the most
calories around the time of conception delivered more boys, with 56% giving birth to male babies, compared with 45% of
women who ate the fewest calories prior to conceiving.
Of those who reported eating breakfast cereal every day, 59% gave birth to
boys compared with 43% of women who reported rarely or never eating cereal for
breakfast, says Mathews.
In addition to consuming more calories prior to conception, women who gave
birth to boys were also more likely to have eaten higher-quality diets with a wider range of nutrients, including potassium.
If nutrition does affect fetal sex selection, Mathews says
it is not clear whether it is calories or nutrients that makes the
What the mothers ate during pregnancy did not seem to influence the sex of
"The mothers who had boys took in about 300 milligrams more of potassium
and about 180 more calories a day than the mothers of girls," she says.
"That is the equivalent of a large banana."