

Chart based on data in the Journal of the American Medical Association.

A major new paper appearing in today's edition of the Journal of the American Medical Association finds that childhood obesity -- age 2 to 5 -- has fallen from 13.9 percent in 2003-04 to 8.4 percent in 2011-12. This age (represented by dark green in the above chart) was the only group to see a significant decline, but it's generating headlines because it raises hopes that these children will remain at healthy weights as they get older. It won't surprise anyone to say that the nation's obesity epidemic poses a major public health problem.

The new paper, by Centers for Disease Control researcher Cynthia L. Ogden and co-authors, doesn't say why childhood obesity is declining. But the paper and several other studies that it cites suggest a number of theories: