ATLANTA - Finally some good news about cholesterol and kids: A big government study shows that in the past decade, the proportion of children who have high cholesterol has fallen.

The results are surprising, given that the childhood obesity rate didn't budge.

How can that be?

Some experts think that while most kids may not be eating less or exercising more, they may be getting fewer trans fats. That's because the artery-clogging ingredient has been removed or reduced in many processed or fried foods such as doughnuts, cookies and french fries.

"That's my leading theory," said Dr. Sarah de Ferranti, director of preventive cardiology at Boston Children's Hospital. She wrote an editorial that accompanies the study.

The study did not look at the reasons for the decline, but its lead author, Dr. Brian Kit of the Centers for Disease Control and Prevention, said the theory makes sense.

The research, released online Tuesday by the Journal of the American Medical Association, also showed that children's average overall cholesterol levels declined slightly.

Too much cholesterol in the blood raises the risk of heart disease. It isn't usually an immediate threat for most children, but those who have the problem often grow into adults with a high risk.

Kit and his colleagues drew data from an intensive national study that interviews people and does blood-cholesterol tests. They focused on more than 16,000 children and adolescents over three periods — 1988-94, 1999-2002 and 2007-10.

During the most recent period studied, 1 in 12 children ages 6 through 19 had high cholesterol. That was down from 1 in 9 during each of the earlier periods — roughly a 28 percent decline.

The average overall cholesterol level fell from 165 to 160. In children, 200 is considered too high.

The study was the first in almost 20 years to show such a decline. Kids' cholesterol levels also fell between the 1960s and the early 1990s, probably because people were eating less fat.