Also, "In only looking at caloric intake over time since the 70's you're also ignoring the other big contributor: decreasing activity levels."

Do you have a citation for that? It's popular to claim that people have become more sedentary since 1980, but I haven't yet found any data to support that claim...and given that the 1980s were boom times for running, cycling, and recreational aerobic exercise in general (a category that didn't really exist previous to then), there's plenty of circumstantial evidence against.

JS