It may simply be that those who have the wherewithal to cook at home--or who earn sufficient income to support a wife who cooks at home or to hire a servant to do it--tend to be those with the cognitive ability to handle the complicated task of managing a healthy and balanced diet.
In terms of attention to the work, my own experience tells me that when people are together in the same room, they pay attention and focus on the task at hand with much of their cognitive capacity.