ATLANTA ó 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 didnít 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. Thatís because the artery-clogging ingredient has been removed or reduced in many processed or fried foods such as doughnuts, cookies and french fries.

ďThatís my leading theory,Ē said Dr. Sarah de Ferranti, director of preventive cardiology at Boston Childrenís 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 childrenís average overall cholesterol levels declined slightly.

Too much cholesterol in the blood raises the risk of heart disease. It isnít 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 ó 1988-94, 1999-2002 and 2007-10.

During the most recent period studied, the number of children ages 6 through 19 with high cholesterol was 1 in 12. That was down from 1 in 9 in each of the earlier periods. 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. Kidsí cholesterol levels also fell between the 1960s and the early 1990s, probably because people were eating less fat and saturated fat. Adult cholesterol levels fell then, too.

The researchers in the latest study detected modest improvements in childrenís levels of so-called good cholesterol, which can protect the heart. That may be partly due to declines in teen smoking and childhood exposure to secondhand smoke over the last decade. Studies have found that chemicals in cigarette smoke can lower good cholesterol.

The bigger news was what happened with bad cholesterol and triglycerides. They went down by small but significant amounts.

In adults, when bad cholesterol levels drop, itís often because patients are using cholesterol-lowering drugs known as statins. But children are rarely given statins.

Last year, a government-appointed panel urged widespread cholesterol screening for children. It was controversial because of concerns it would lead to more kids being given medicine. Experts say statins should be used in only the worst cases ó less than 1 percent.

Artificial trans fats are known to decrease good cholesterol and increase bad cholesterol. In 2006, the federal government began requiring that packaged foods list the amount of trans fat per serving, a boon for careful shoppers.

Meanwhile, a push to take trans fats out of foods gained momentum. New York City banned artificial trans fats in restaurant food in 2008. California in 2010 became the first state to adopt such a ban.