is inactivity the problem?
Read this very interesting study which attempts to compare energy expenditure between typical Western lifestyle vs a pre-modern gatherer one. Indications are that the latter is not more energy intensive than the former, which blows a hole in the popular idea that people are fat and unhealthy because they don't "do" anything.
Which leaves the blame for the dis-health epidemic squarely where it belongs: on high-energy foods empty of real nutrition.
Here is a link that might be useful: busy little gatherers