Sure, I think that's a very plausible explanation. It also points to specific, testable policy changes. For example, a government could build a low cost (subsidized), healthy competitor to fast food. Alternatively, a government could implement a comprehensive "sin tax" scheme on "low quality" calories coupled with expanded food stamps (to ensure the poorest people can afford healthy alternatives). Governments could even go into food desserts and open health-focused grocery stores. We could see if low cost/low quality calories are the issue via a legislative experiment.
I've often thought that government-run "soup kitchens" providing basic nutritional food in small portions should be everywhere - no requirements to eat there, if Bill Gates and Buffet want to have lunch at the free soup kitchen who cares.
I like the Japanese school-lunch system. Kids develop a familiarity with real food, which stays with them into adulthood (and reduces the likelihood of obesity ever occurring), and parents don't have to worry about it.
