Great question, and no good answer exists. That why it should be avoided in such studies. There is, however, the traditional Okinawa diet. This is much better

Great question, and no good answer exists. That why it should be avoided in such studies. There is, however, the traditional Okinawa diet. This is much better defined (a much small geographic region), and know to be one of the healthiest in the world. There's this book Blue Zones, that talks about this.