A new study which was published in this week's New England Journal of Medicine and paid for by the U.S. government finds that much of a child's "weight fate" is set by age 5, and that nearly half of kids who became obese by the eighth grade were already overweight when they started kindergarten. The prevalence of weight problems has long been known -- about a third of U.S. kids are overweight or obese. But surprisingly little is known about which kids will develop obesity, and at what age. Researchers think there may be a window of opportunity to prevent it, and "we keep pushing our critical window earlier and earlier on," said Solveig Cunningham, a scientist at Emory University. "A lot of the risk of obesity seems to be set, to some extent, really early in life." It tracked a nationwide sample of more than 7,700 children through grade school. When they started kindergarten, 12 percent were obese and 15 percent were overweight. By eighth grade, 21 percent were obese and 17 percent were overweight. Besides how common obesity was at various ages, researchers focused on the 6,807 children who were not obese when the study started, at kindergarten entry. Here are some things they found: WHO BECAME OBESE: Between ages 5 and 14, nearly 12 percent of American children developed obesity -- 10 percent of girls and nearly 14 percent of boys. Nearly half of kids who started kindergarten overweight became obese teens. Overweight 5-year-olds were four times as likely as normal-weight children to become obese (32 percent versus 8 percent).
AP Photo/Jim Cole - First lady Michelle Obama does a bunny hop dance with pre-schoolers at the Penacook Community Center in Concord, N.H., as part of her Let's Move initiative. A new study finds that much of a child's "weight fate" is set by age 5.