BioEd Online

It might not seem inevitable that overweight mothers will have fatter babies. But this is exactly what's happening in the United States, say researchers who have documented how the 'obesity epidemic' is being passed on to the next generation.

The team, based at Harvard Medical School in Boston, Massachusetts, has found that the proportion of overweight babies has risen by almost two-thirds over the past two decades, so that 10% of babies now fall into this category. And the proportion of babies at the upper end of the weight scale termed 'at risk of becoming overweight' has risen by a third to 14.

The group, led by Matt Gillman, followed more than 120,000 children between birth and 6 years of age, monitoring their weight and height. Infants from birth to 6 months old showed a particularly large increase in obesity from the 1980s to the 2000s, they add.

A mother who gains a lot of weight during pregnancy can predispose her child to being overweight for life, says Gillman, who reports the work in the journal Obesity¹.

In extreme cases, putting on excessive weight when pregnant can lead to a condition called gestational diabetes in the mother. Studies of the disorder in rats show that it increases levels of the hormone insulin in pups. High insulin levels then boost appetite by acting on the hypothalamus, a part of the brain responsible for regulating food intake, he says. It seems the same thing can happen with people too.

"Gestational diabetes can programme babies," says Gillman, to make them overweight.

In less extreme cases, a mother or father's weight may pass on messages to a developing child through egg, sperm, or conditions in the womb: not by changes in DNA sequence, but by altering how the DNA is expressed. Exactly how this might happen is as yet unclear.

Of course, diet could be expected to have an effect too. Breast-fed babies typically gain weight more slowly than those fed on formula milk. This is in part because the composition is different: in the first few feeds, breast milk provides immune factors, and fattier milk comes only later; the make-up of formula milk, however, is constant. It is also partly because of a difference in feeding patterns. "A breast-fed baby has a lot of control over the amount of milk it gets, whereas a bottle-fed baby has rather little," says Tim Cole, of the Institute of Child Health in London, UK. "A bottle-fed baby will be given as much as the mother thinks they should have."

But the rate of breastfeeding has been increasing, not decreasing, as the number of overweight babies has risen. Gillman says breastfeeding probably goes some way towards counteracting this trend babies would probably be even fatter if mothers did not breastfeed, he says.

Is it really that bad for babies to be a bit plump? Many infants do lose their baby fat, says Gillman. But overweight infants are also more likely to become overweight adults, particularly if their appetites have been 'programmed' at a different level. This can predispose them to chronic disorders such as high blood pressure and diabetes.

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