[ascott]

There was a study of the town Roseto, Pennsylvania in the 1950s that may explain why this is the case. They ate a traditional american diet, exercised the same amount as other americans, etc. But they had almost no heart disease, which was astounding at the time.

The difference was that everyone in town was very social. They would frequently share meals with neighbors, and several family generations would live together under the same roof. The conclusion the study came to was that the excellent health was from community and social connections.

http://www.nytimes.com/2008/11/30/books/chapters/chapter-out...

I think these social connections become necessary for survival in poor areas. So they are resistant to diseases of affluence when their diet changes.