(CNN) — The baby fat lingering around your 5-year-old's face (and tummy and thighs) may be an indicator of his or her weight for many years to come, a new study suggests. Children who enter kindergarten overweight are four times more likely than their normal weight peers to become obese by age 14, researchers say.
Though recent studies have shown signs of progress in the fight against childhood obesity, an estimated one out of every eight preschoolers in the United States is obese, according to the Centers for Disease Control and Prevention. The numbers are higher in African-American and Hispanic populations, at one in five and one in six, respectively.
The new study, published Thursday in the New England Journal of Medicine, suggests a big part of a child's obesity risk is already established by age 5. Interventions to combat childhood obesity may need to focus on those children who are overweight early in life, the study authors say.
Body mass index for children is calculated a bit differently than it is for adults. While kids' height and weight are still used, whether they are "normal," "overweight" or "obese" is determined by a percentile. Most parents are familiar with percentiles, as they are commonly used to chart children's growth in the United States.
A healthy weight child falls between the 5th and the 85th percentiles. An overweight child is the 85th to 95th percentile; an obese child is above the 95th percentile.
Researchers analyzed data from more than 7,700 children who started kindergarten in 1998. The children's height and weight were measured seven times between that year and the time they turned 14 in 2007.
At the start of the study, 12.4% of the children were obese, and another 14.9% were overweight.
The researchers then determined the overall obesity incidence each year, and broke down the obesity rates by sex, socioeconomic status, race or ethnic group, birth weight and kindergarten weight.
By the eighth grade, 20.8% of the children in the study were obese and 17% were overweight.
Half of the children who were obese at 14 had been a part of the 14.9% who were overweight as kindergarteners; 75% had been in the 70th BMI percentile or above.
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The greatest increase in obesity rates was seen between first and third grades when the incidence jumped from 13% to 18.6%.
Children in the wealthiest families were the least likely to be overweight. Children who were born heavier -- i.e., more than 8.8 pounds -- had a higher risk of being obese at every age.
Doctors and teachers can't fight childhood obesity without help, Steven Gortmaker and Elsie Taveras wrote in an accompanying editorial in the journal. Improving a child's diet and increasing physical activity levels at home can reduce early weight gain and the risk of obesity.
How do you keep your children active? Share your tips with other parents and experts during a live Twitter chat at 1 p.m. ET Friday, hosted by @CNNHealth and celebrity trainer David Kirsch. Use the hashtag #FitFamilies to join in.