They work, not office work, physical work. So even if their genes favor obesity, they're slim. So says this study.
I buy it. A rural society with lots of physical labor is not stout. "Stout" is a word from the past. Of course many so-called farmers now have a pot, "so-called" because they just drive tractors and because I'm feeling grumpy today. Contra Professor Pollan, the key variable is not the diet, it's the labor.
(Decided since I'm fascinated by the Amish, I need to add a tag for them.)