article

09.12.10

Will Your Baby Be Obese?

Does your child get enough sleep? Does your baby drink formula? New research suggests that our blueprint for obesity is established very early in life. Joyce C. Tang on how a toddler’s habits can predict whether he’ll be a fat adult.

Could a sleep-deprived child grow up to be an overweight adult? There may be a correlation, according to a new report, which found that toddlers who slept less than eight hours a night were more likely to go from normal weight to overweight or obese.

Conventional wisdom holds that fat parents lead to fat children, either because of genetics or learned behaviors, or a combination of both. But a growing body of research suggests that there may be a third, separate factor. Health experts are examining the links between a child’s very early life—sometimes even the period before birth—and the probability that that child will grow up to be obese.

Danielle Friedman: Home-Birth Horror Stories“The early-life field is in its infancy,” says Emily McAllister, a researcher who studies obesity at the Pennington Biomedical Research Center in Baton Rouge, Lousiana, though a version of it emerged some 20 years ago in the Barker hypothesis. Named after physician David J.P. Barker, the theory says that fetal development is highly correlated to chronic conditions later in life, including heart disease and diabetes. And now, increasingly, “We are beginning to find evidence of a blueprint for obesity,” McAllister says, meaning that what happens to us in the months prior to or soon after birth can sometimes set a life course for weight gain that’s difficult to alter.

The sleep link is just one of many. The researchers in that study offered a few explanations for why small children who sleep less might become overweight. "It may be that children who don't sleep enough at night are too tired to engage in the kind of physical activity that may prevent obesity," researcher Janice Bell told NPR. She also speculated that sleep could influence the release of hormones that control appetite.

“If you have a genetic code that’s prone to obesity, and in utero you’re exposed to an obese genetic environment, then that can affect the way genes are expressed.”

If your sleepless toddler is using that extra awake time to watch television, he or she could be in even more trouble. Research has shown that excessive TV watching before age 3 makes one vulnerable to obesity. Though many assume there’s a “couch potato” effect—kids not burning calories because they’re camped out in front of the tube—a recent study found evidence that the true culprit was the type of television kids were watching. Viewing ads and commercials, many of which happen to promote junk food, versus educational television, had a greater association with obesity.

Shorter periods of breastfeeding have also been shown to put children at risk for obesity, though its direct effect is difficult to parse, as these households tend to be more educated and affluent. Infants who don’t breastfeed are reliant on formula, which is consumed in higher volumes because, some speculate, it contains lower-quality nutrition than breast milk. The higher-volume intake could also set a higher bar for feeling full, and there tends to be rapid weight gain with formula, a warning sign for obesity.

Other research has found links that go all the way back to the womb. While most obesity intervention programs are targeted toward children of school age, early-life studies imply that our focus should be shifted to mothers and the time immediately surrounding pregnancy. For instance, slimming down before becoming pregnant may help derail a child from a lifetime of struggling with his or her weight and, in effect, put an end to a family’s cycle of obesity. “It offers one potential intervention that may be effective,” says Robert Waterland, an assistant professor of pediatrics at Baylor College of Medicine.

Waterland’s research is based on epigenetics, an emerging area of science that looks at how the expression of genes is influenced by the environment. It’s a subtle though scientifically dramatic shift away from the assumption that genes passed down directly from our parents determine obesity. “If you have a genetic code that’s prone to obesity, and in utero you’re exposed to an obese genetic environment, then that can affect the way genes are expressed,” McAllister explains.

Even if a mother doesn’t start out overweight at the time of pregnancy, packing on excessive pounds over three trimesters increases the chances that her child will be obese. In one recent study, women who gained more than 50 pounds during their pregnancy were more than twice as likely to give birth to heavier babies—high birth weight being another predictor.

These findings indicate “that the ideal time to begin obesity-prevention efforts is before birth,” writes Dr. David Ludwig, one of the authors of that study, “and that the type and amount of food a woman eats during pregnancy may have lasting consequences for her offspring.”

Mothers who put on excess weight during pregnancy are also more likely to develop insulin resistance, which can lead to gestational diabetes. Though it’s unclear how gestational diabetes causes babies to carry excess fat, some think that the womb environment leads to metabolic changes in the fetus. High blood glucose levels from eating sugary foods can have a similar effect.

Though overeating and unhealthy eating while pregnant may be an obvious path to obesity for the child, undernourished fetuses can also end up as overweight children or adults. In a classic study of men born during the Dutch famine following World War II, maternal malnourishment was shown to lead to a high prevalence of obesity by age 19. Researchers think that when an infant develops in a womb where nutrients are lacking, it’s prone to “catch-up growth” and excess fat storage. It’s a good evolutionary defense mechanism when food is scarce, but makes the child more likely to be obese when he or she subsequently grows up in an environment where food is plentiful.

Yet another early blueprint for obesity might be the age of the mother—and some experts say that the shift toward older motherhood in America may be a part of what’s driving the country’s out-of-control obesity problem. Compared with women age 25 to 29, mothers age 30 to 34 were 24 percent more likely to have large babies, and mothers older than 35 were 42 percent more likely to give birth to heavy babies. Older mothers, whose metabolism tend to be more sluggish than the generation of younger mothers before them, also tend to be heavier. In addition, with aging comes insulin resistance. But the age effect on obesity remains even after researchers control for these potentially confounding factors.

Mothers seem to bear the brunt of the destiny of their child’s weight, but fathers shouldn’t be discounted. A child’s chances for obesity are greatly increased if the dad is also overweight, though whether their influence is beyond genetic has yet to be investigated. While some may say that our exploding obesity epidemic is a hyperbole, fat does beget fat. The obese population has a higher rate of reproduction, leading to a seemingly exponential obesity problem.

Though early-life factors seem to indicate a doomed destiny for some, they can also provide new avenues of attack. For instance, shedding some pounds before pregnancy could help overcome what many have previously thought was a losing battle with weight. And it may very well be the best gift a mother can give her child.

Joyce Tang is a writer based in New York City. Her work has appeared in Mother Jones, Double X, and The Miami Herald.