I've a firm belief that the ability to extract nutrients depends on the genetics.
So changing your environmet or diet can have adverse effects like more diseases. Even lifestyle shouldn't be changed drastically in my opinion, even if someone pays you more to do exactly that.
Gene function depends on the nutrition and environment.
Genes learn slowly, so things must change a little over generation for learning to happen.
Ofcourse, a Human tribe is resilient to drastic changes lik famine, but please not that a large portion of the tribe gets wipped during such transition.
I would love to see the research backing for my belief.