Counterpoint:There're areas where people eat organic food, not everyone eats at McDonalds.
I'm an American, I eat organic low-calorie food and I'm super-lean. I often find myself in towns where most are very lean.
As Johnathan Haidt points out, your individual IQ matters relatively little to success but the average IQ of your group matters a lot. Success is formed through productive group cooperation.
I imagine the same thing is true of other mental attributes beyond strictly IQ. Such as the discipline needed to not be a lard bucket.