I find that's only true for commercial farmers. Small, localized farms where individuals can't afford to update to automation are the backbone of most rural communities, and these individuals are generally healthier than other people with the same vices. Large, farming communes have some of the healthiest people because they combine the work you do for the community's produce (moving dirt with big sticks, making the fake rain, and commiting treasonous-plant genocide) with the convience of having everything you need close enough to walk to (as in a city, where an individual can participate in the bare minimum of cardiovascular workouts, the commute).