Wednesday, March 24, 2010

'Eating for two' may harm baby

Pregnant women are often assumed to be “eating for two”, but a high-calorie diet may also be influencing the sex and health of their child, researchers say.

A study in pregnant mice found that diets which were high in fat or carbohydrates had an effect on almost 2,000 genes in the developing offspring, including those involved in kidney function and smell.

The most striking variations were found in those of the female foetuses, suggesting that girls may be more susceptible than boys to genetic changes triggered by their mother’s diet.

Sons and daughters are also at different risk for conditions such as obesity or diabetes 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 study, published the Proceedings of the National Academy of Sciences, follows previous research that suggested that a woman’s diet around the time of conception may influence the gender of her baby.

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 more likely to give birth to a girl.

However, researchers say that there could be several confounding factors that determine the sex or health of a baby, including that mothers who are overweight or obese being at greater risk of miscarriage or stillbirth.

The latest study examined the effects of high-fat and high-carbohydrate diets on the placenta, the barrier between mother and baby, compared to mice given normal soybean meal-based food.

Dr Cheryl Rosenfeld, of the University of Missouri, and colleagues write: “Diet during pregnancy influences the future health of a woman’s offspring, with outcomes differing depending on the child’s sex."

They concluded that gene expression in the mouse placenta is “adaptive and shaped by maternal diet” with the biggest effect on the placentae of females.

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 years.

Some researchers have suggested this could be because women have been consuming low fat foods and skipping breakfast, among other things.

“Maternal diet also may influence the sex of offspring born in certain mammalian species, including mice and humans,” the authors conclude. “High calorie diets generally favour birth of males over females, whereas low calorie diets tend to favour females over males.

“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.”

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