According to a new U.S. study, extreme obesity among American children is much worse than previously believed, putting them at greater risk of serious health problems as they age.  

A new Californian study sought to determine how many children in a section of Southern California were extremely obese under a new U.S. Centers for Disease Control and Prevention definition. Previous research based on a federal health survey suggested that 3.8 percent of children were extremely obese. But this latest study, reported in the Journal of Pediatrics, found that of the 700,000 children and teens in Southern California studied, more than 6 percent, or 45,000, were extremely obese.  

Doctors do not define obesity in children the same way they do for adults. Obese children are defined as those whose weight is above the 95th percentile for their age and height and extreme obesity is 1.2 times that measurement.

For this study, researchers looked at health records of 710,949 children and teens aged 2 to 19 enrolled in a managed health care plan in 2007 and 2008. The group was almost evenly split between girls and boys and about half were Hispanic.

The study found that 7 percent of boys and 5 percent of girls were extremely obese, as were more than 2 percent of all children under 5 years old. The heaviest children were black teenage girls and Hispanic teenage boys.

First lady Michelle Obama is leading an administration effort to fight childhood obesity focused on improving nutrition in homes and in schools.

Childhood obesity: It's worse than you thought
Extreme obesity among American children is much worse than previously believed.