As a family doc with over 25 yrs of patient experience I have no doubt that lack of physical activity during the day is the main issue here.
People who stay physically active are generally not obese. I wish the education system would realize this, kids need to move, I don't really care what kind of sport or exercise they do. Employers or the government should encourage, and likely pay for, employees exercise. A physically strong human feels happier, and is more productive.
The human body is an animal, it is really not designed for the computer age. :)
Animals move, otherwise you are a plant :)