From the rhetoric coming out of last weekend’s obesity-lawsuit-pushing Public Health Advocacy Institute (PHAI) conference in Boston, you’d think snack foods and soft drinks were the number one cause of childhood obesity. But the sue-first-ask-questions-later food cops and trial lawyers apparently didn’t bother to consult researchers across town at Harvard, who last week provided the latest evidence that snack foods and soda are actually not a cause of childhood obesity.

After studying more than 14,000 American children, a team of six Harvard doctors found that snack food and soda do not contribute to childhood obesity. The study, which was published in the October issue of the International Journal of Obesity, concluded: “[O]ur data did not offer support for the hypothesis that snacking promotes weight gain.” Earlier this year, researchers at Penn State reported substantially the same thing. They found “no statistically significant relationship between the percentage of calories from ice cream, baked goods, candy or chips and BMI [Body Mass Index] score” for adolescent girls.

The Harvard research specifically contests what is perhaps public-health activists’ most cited study — a 2001 paper by fat-tax advocate David Ludwig, which claimed that soda consumption is a major factor in childhood obesity. After referring to Ludwig’s conclusion, the Harvard study reports:

[T]he inclusion of sugar-sweetened beverages in the snack food category did not meaningfully change the results. Regardless of the definition of snack foods, there was not a strong association between intake of snack foods and weight gain.

There is good reason to believe the recent Harvard report over Ludwig’s. With only 548 children to study (versus Harvard’s 14,000), Ludwig admits that his study had “limited statistical power.”

The new Harvard study helps reinforce the growing understanding that physical activity, not food, is the primary cause of childhood obesity. According to former FDA Commissioner Dr. Mark McClellan: ““…it’s perhaps surprising that, in a debate that has often focused on foods alone, actual levels of caloric intake among the young haven’t appreciably changed over the last twenty years.”

A growing body of research corroborates McClellan’s point. Earlier this year, research published in the Archives of Pediatrics and Adolescent Medicine found that “insufficient vigorous physical activity was the only risk factor” for overweight children. And a 2003 study in the American Journal of Preventative Medicine summed it all up by recommending “a focus on increasing energy expenditure, rather than reducing caloric intake.