To me, looking at pictures of "ordinary" Americans from the 40's and 50's, is how slim most people were compared to today.

Obesity wasn't an epidemic, Diabetes Type II didn't appear in 10-year-olds. A woman with a matronly figure was in her forties and fifties, not in her teens and twenties. Likewise a guy with a belly.

At the turn of the century, a "circus fat man" looked exactly like someone in any mall in the country. We are talking a time span of only a century.

That is environment. Not genetics.