FRIDAY, Dec. 31 — American kids are becoming obese, or nearly so, at an increasingly young age, with about one-third of them falling into that category by the time they're 9 months old, researchers have found.
There are some caveats about the research, however. The infants were not studied recently: They were born about a decade ago. And it's not clear how excess weight in babies may affect their health later in their lives. The study found no guarantee that a baby who's overweight at 9 months will stay flabby when his or her second birthday rolls around.
Still, the study — in the January-February 2011 issue of the American Journal of Health Promotion — does present a picture of babies and infants who are carrying around a lot of extra weight.
The findings also suggest that small changes in an infant's diet can make a big difference, said Dr. Wendy Slusser, medical director of a children's weight program at Mattel Children's Hospital at the University of California, Los Angeles. For example, she said, "if you don't give your kid juice and have them eat the fruit instead, suddenly there's 150 calories less a day that can make a big difference in weight gain over a long term."
The researchers examined federal data about 16,400 children in the United States who were born in 2001. After adjusting the statistics so they wouldn't be thrown off by such factors as high numbers of certain kinds of kids, the study authors found that 17 percent of 9-month-olds were obese and 15 percent were at risk for obesity, for a total of 32 percent.
At two years, 21 percent were obese and 14 percent were at risk of becoming obese, the investigators found.
"It seems like there tends to be a shift to kids getting heavier" over time, said the study's lead author, Brian G. Moss, an adjunct faculty member at Wayne State University School of Social Work. And their weight gain, he said, is beyond that which would be expected as youngsters grow.
Hispanics and poor kids as a whole were at highest risk, the study found, whereas girls and Asian/Pacific Islanders had the lowest risk.
But why are young children so heavy and getting heavier, as a whole, over time? The study didn't examine the reasons. Moss said the changes could have something to do with changes in their lives, such as entering daycare or starting to eat regular food, but the precise causes are not clear.
However, the research does suggest that infants aren't doomed to be overweight once they put on extra pounds, said Slusser, the children's hospital medical director. "There's this fluidity," she said, "a lot of movement back and forth into these categories."
So what is her advice for those who have an infant or one on the way? "You really need to reflect on the habits you have with your child," Slusser said. For instance, make sure the infant gets regular meals and snacks along with a good night's sleep and naps, she said. And pick a daycare center that offers healthy foods and opportunities for moving around.
And breast-feeding, she said, is ideal — especially during the first six months, when specialists recommend that breast milk should be the exclusive source of food for babies.
The Nemours Foundation offers more on breast-feeding versus formula feeding.
Follow Yahoo! News on Twitter, become a fan on Facebook