As opposed to a sedentary lifestyle spent passively consuming entertainment from the safety of environmentally controlled living spaces that requires little energy to be expended on any activities.
US obesity rates and dental problems started skyrocketing around war time, when sugar was introduced to soldiers' rations and by virtue of subsidies into mainstream diet. Many of life's comforts like cars or TV sets (and radios before them) were available in that era.
At the same time countries with low obesity rates exist today, and residents of Thailand, Moldova or Japan are not particularly deprived of cars, TVs or PCs, nor do they exert significant physical effort to hunt and gather their food.
On the other side of the spectrum, countries with high obesity rates (Mexico, Nauru, Cook Islands) are not particularly car-infested way way higher when compared to peers, nor do they have extreme TV/PC consumption numbers.
The only relevant variable seems to be the amount of sugar (consumed from all sources) in the diet.
The sedentary lifestyle theory does help sell fitness club memberships, though, so it's not completely useless.
http://www.telegraph.co.uk/news/health/news/9405918/British-...
I don't know if anyone has good data on the amount of walking per capita per country. Maybe FitBit would have decent stats, but then their userbase is a bit self-selecting.
No. http://wholehealthsource.blogspot.com/2012/02/by-2606-us-die...
It was relatively hard to produce, expensive to import, and the scientists did not yet invent high-fructose corn syrup.
The real money for the food industry then became pursuing the low-fat diet.
It's only been recently that the medical community has realized that sugar is actually the number one hidden danger in the modern diet.