OK, and how does a person do that? You can't blame it on sloth and gluttony, because the problem is too big, worldwide, and the VAST majority of attempts to lose weight, or not gain it, fail. No one wants to be obese and every obese patient tries many times and fails to lose the weight and keep it off, and it's not just here in the U.S. but the western world.
So until you can explain what changed about 50 years ago, when we all just went about our day, never worried about calories or fat, and did NOT get obese, to today when 40% of the adults in my area are obese, then saying what you did is true but meaningless, because it doesn't help avoid obesity or solve it for the 40% in this country suffering from it.
And staying active is not the solution. People in every walk of life including blue collar workers, nurses, doctors, clerks on their feet 8 hour shifts per day, etc. are obese. Also, comparing 'activity' levels doesn't explain obesity. 50 years ago who heard of going to a gym? Weight lifters etc. and that's about it. Now there are workout facilities on every corner and it doesn't dent the problem - it gets worse every year. A massive fitness industry emerged since the 1960s and obesity increases every year. Exercise is awesome for lots of reasons, just not for losing weight or controlling diabetes. It helps there, but on the margins, which means if you don't solve the other problems, our diets, exercise will prove futile long term. The issue is what about our diet explains the problem.