Overweight children are often said to have baby fat that will disappear as they get older, but a new British study suggests this is a myth.

In reality, overweight kids are more likely to become overweight teens, increasing their risk for diseases linked to obesity, such as type 2 diabetes.

"Contrary to our expectation, children who are overweight at 11, stay that way right through to 16, with no sign that they were growing out of their 'puppy fat,' " said lead researcher Jane Wardle, director of the Cancer Research UK, Health Behavior Unit in the Department of Epidemiology and Public Health at University College London.

In the study, researchers collected data on 5,863 children as they developed into young adults. The results clearly showed that weight problems are established before adolescence. The researchers found that children who were overweight when they were 11, continued being overweight through adolescence.

Their report appears in the May 4 online edition of the British Medical Journal.

The research team found that 25 percent of children were overweight. Girls had greater weight problems than boys. Black girls particularly were more likely to have weight problems, with an average of 38 percent being overweight or obese over the study period, compared with 28 percent of white girls and 20 percent of Asian girls. However, among boys, ethnicity made little difference in weight.

Economics also played a role, with those from the lowest economic background more likely to be overweight. Among girls, 35 percent from the lowest economic background were overweight or obese, compared with 28 percent of other girls.

Wardle sees these findings as a warning sign of future health problems. "Obesity, which is developing before 11 in childhood, is persistent obesity rather than a temporary stage children are going through," Wardle said. "Parents have to take action earlier. And, as a society, we have to recognize that what's going on with the children is a future time bomb and not just a passing phenomenon."

One expert sees the same pattern of obesity among U.S. children.

"The data are worrisome," said Dr. Walter Willett, the Frederick John Stare Professor of Epidemiology and Nutrition at Harvard Medical School and chairman of the Department of Nutrition at the Harvard School of Public Health. "They show the same pattern that we see here of continued high levels of overweight and obesity," he said.

Overweight is a problem that is showing up earlier in childhood, Willett said. "We need to be putting more emphasis on younger children," he noted.

Childhood obesity needs to be attacked from many directions, Willett said. "Health-care systems need to be giving more attention to counseling the whole family about weight control," he said. In addition, Willett believes that schools need to do a better job in promoting healthy eating and in increasing physical activity both during and after school.

Willett noted that the racial and economic disparity in overweight children seen in the British study is seen in the United States as well. "This is heavily wound up in economic disparities, educational opportunities, the physical environment and food availability," he said.

Willett believes that parents can play an important part in keeping their children from becoming overweight. "That means setting a good example," he said. "Not buying junk food. Soda doesn't belong in households. Parents who are eating well and being active are setting a good example, and that's really important," he said.

"Healthy weight control is a life skill," Willett added. "We focus on childhood obesity a lot, but still the biggest weight gain comes on after age 20," he said. Controlling weight is a lifetime task. "It needs to be almost from birth to death," he said.

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