In a newly reported study, women who ate breakfast cereal gave birth to more boys, while those who skipped breakfast had more girls.
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 50/50.
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 WebMD.
"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."
Fewer Calories, Fewer Boys
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 pregnancy.
They were also asked to recall their dietary habits in the year prior to conceiving.
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.
What the mothers ate during pregnancy did not seem to influence the sex of their babies.
"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."
The Importance of Breakfast
So should a woman who wants her next child to be a girl skip breakfast and limit calories?
Absolutely not, says American Dietetic Association spokeswoman and registered dietitian Elisa Zied.
"Whole-grain cereals are loaded with folic acid, and so are oranges and orange juice," she says. "If you skip breakfast, you could easily not get enough."
She adds that eating a balanced diet prior to conception and during pregnancy is one of the best things a woman can do to ensure a healthy pregnancy.
"That means eating regular, frequent meals, eating plenty of fruits and vegetables and foods rich in folic acid and other nutrients, and avoiding alcohol," she says.