Double Trouble

Every pregnant woman knows she's eating for two. But if she indulges too much during the nine months she's carrying her baby, she could be creating serious weight-loss problems for two, as well.

That's the latest theory among researchers trying to unravel the mystery of the childhood-obesity epidemic. Though the startling three-decade rise in childhood obesity appears to have leveled off, according to a new study published in this week's issue of the Journal of the American Medical Association, researchers say the rate is still way too high: more than three times that of the 1970s. Doctors have long known that children's lifestyle habits—how much they eat and exercise—play a role in determining whether they gain too much weight. But the role of genetics has been less clear, says Dr. Thomas M. Badger of the USDA-Arkansas Children's Nutrition Center. Some data seem pretty straightforward: bigger moms tend to give birth to bigger newborns, who often become heavier than normal children and prove to be at high risk for becoming obese adults. These correlations seem to suggest that much of obesity is genetically predestined.

Overweight women don't always produce overweight kids, but researchers noticed that kids were much more likely to have weight problems if they had an overweight mother than a heavy dad. They wondered if excessive weight gain before or during pregnancy might directly affect the metabolic programming of the developing fetus. In other words, could an overweight pregnant woman be creating an environment inside her uterus that predisposed her child to put on fat more quickly than the offspring of normal-weight mothers, even when both groups of babies ate similar foods and got the same level of exercise?

To begin to answer this question, the Children's Nutrition Center completed a study, published early this year in the American Journal of Physiology, in which they overfed one group of normal-sized female rats (to eliminate the possibility of inheritance of obese genetic influences) before mating them with lean males. A second group of normal-sized females was fed a healthy diet before being mated with similarly sized males. After all the pups were born and weaned, both groups were fed a high-fat diet. After 130 days on the diet, the offspring of the obese females were four times heavier and put on 60 percent more subcutaneous and abdominal fat, even though the calorie intake of both groups was the same.

"They were programmed differently, so they responded differently," says Badger. "We think there's a high likelihood that something similar is happening in humans, in terms of programming kids to become overweight later in life."

However, that doesn't mean that everyone who is obese is metabolically programmed in utero, he says. The issue of why children become obese and overweight is "very complex," and there isn't a single explanation. But researchers want to identify who might be affected and understand the mechanism involved so they can help prevent mothers from unwittingly predisposing their unborn children to putting on fat more quickly. (Once a child is older, Badger says, obesity is much more difficult to reverse.)