The rate of severe obesity among U.S. children and teenagers more than tripled over the past three decades, a new study finds.

Using data from a long-running government health survey, researchers found that as of 2004, nearly 4 percent of 2- to 19-year-olds in the U.S. were severely obese.

That was up more than three-fold from 1976, and more than 70 percent from 1994, the researchers report in the journal Academic Pediatrics.

"Children are not only becoming obese, but becoming severely obese, which impacts their overall health," lead researcher Dr. Joseph A. Skelton, of Wake Forest University School of Medicine in Winston-Salem, North Carolina, said in a news release from the university.

"These findings," he added, "reinforce the fact that medically-based programs to treat obesity are needed throughout the United States and insurance companies should be encouraged to cover this care."

The study also found that minority and lower-income children are at particular risk of severe obesity — which, in children and teenagers, is defined as having a body mass index (BMI) in the 99th percentile for one's age and gender.

In the most recent survey, which included 12,000 2- to 19-year-olds from across the U.S., nearly 6 percent of African-American children and teens were severely obese, as were roughly 5 percent of Mexican- Americans. That compared with 3 percent of their white peers.

In contrast, less than 1 percent of Mexican-American children and less than 2 percent of black children were severely obese in the 1970s survey.

When it came to family income, the latest survey data show that just over 4 percent of relatively lower-income children were severely obese, versus 2.5 percent of those from higher-income families.

The findings underscore a central obstacle in tackling childhood obesity, Skelton and his colleagues note: The children who are most affected also generally have the greatest difficulty getting good healthcare.

"No simple answers exist," the researchers write, pointing out that along with better access to healthcare, there also need to be broader efforts to improve the diets and lifestyle habits of U.S. children.

SOURCE: Academic Pediatrics, September 2009.