Women who eat a full breakfast and
a high fat diet at the time of conception are more likely to have a boy,
A low fat diet with periods of long
fasts favours girls, the researchers have found.
The findings seem to give some
credence to old wives’ tales such as eat “bacon for boys”.
Dr Cheryl Rosenfeld, of the
University of Missouri, and colleagues said: “High calorie diets generally
favour birth of males over females, whereas low calorie diets tend to favour females
“In humans and mice, food
restriction and a suboptimal diet during the period around conception and early
pregnancy also lead to a surfeit of daughters, most probably due to selective
loss of male foetuses, the most vulnerable sex in the womb.”
Researchers analysed the genes in
placentas of pregnant mice fed diets high in fat or carbohydrates and low
calorie diets and found each one had a distinctive effect compared with a third
group given normal soybean meal-based food.
As well as the changes in sex,
female foetuses were more sensitive to their mother’s diet and their genes were
more likely to be affected or altered, it was found.
They concluded gene expression in
the mouse placenta is “adaptive and shaped by maternal diet” with the
biggest effect on the placentas of females.
The research was published in
Proceedings of the National Academy of Sciences.
A high-calorie diet at this time –
and regular breakfasts – might increase the odds of a boy while women with a
lower energy intake were likelier to give birth to a girl.
The research shows a higher calorie
intake around the time of conception can shift the odds of having a son from
ten to 11 boys in every 20 births.
Sons and daughters are also at
different risk for diseases later in life, apparently related to either the
mother’s diet or body condition while pregnant.
For instance, sons of obese mothers
are more likely than daughters to become obese and develop diabetes as they get
older, even though no differences in birth weight may be evident.
The researchers added: “The
reason why a maternal high fat, low carbohydrate diet favours survival of sons
and a maternal low fat, high carbohydrate diet results in more daughters
continues to elude us.
“The effect was such that the
more women ate the more likely she was to have a boy.
“Women who had sons were also
more likely to have eaten a higher quantity and wider range of nutrients
including potassium, calcium and vitamins C, E and B12. They were also more
likely to have eaten breakfast cereals.”
There has been a small but
consistent decline of about one per 1,000 births annually in the proportion of
boys being born in industrialised countries, including the UK, over the last 40
It could be because women have been
consuming low fat foods and skipping breakfast, among other things.