Finally some sanity in this thread. Thank you. You are exactly correct. Obesity (as well as the associated chronic diseases) are directly caused by diet: particularly carbohydrates and pro-inflammatory oils.
Clearly man’s genome hasn’t changed in the past 50 years of rampant obesity and diabetes; nor has our behavior. We all didn’t suddenly get lazy. What has changed is our diet. We are stuffing ourselves with carbohydrates (refined or not), sugars of every sort, and bad oils. At the same time we are shunning healthy oils such as saturated fat.
Yes, diet can correct it for just about all of us, it seems.
But there also was a major downswing in physical labor and exercise for many Americans between the early and late 20th centuries.
Move into Midtown Manhattan and for the same amount of calories you will likely maintain or lose weight. Then go out to the car-dependent ‘burbs again and without dietary adjustment, your weight will start to climb.
(I know both of these truths from personal (albeit, by definition, anecdotal) experience.