The authors accounted for gender, race, income and school location.
Taber noted that several Southern states have been the most aggressive at targeting school junk food, "probably because they have the highest rates of obesity."
Ludwig, the Boston obesity specialist, praised the researchers for trying to "tackle a complicated question."
"The challenge is that there are a great many factors that coalesce to influence body weight," Ludwig said. "Disentangling these influences and looking at the independent effects of just one is a methodological nightmare."
AP Medical Writer Lindsey Tanner can be reached at http://www.twitter.com/LindseyTanner
Copyright 2012 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.