This is orthogonal.

One guy getting in a better shape after diet and exercise is quite expected.

Whole society being virtually free of big bad diseases is, on the other hand, extraordinary claim:

"When it comes to the top 10 health risks facing American men, the Tarahumara are practically immortal: Their incidence rate is at or near zero in just about every category, including diabetes, vascular disease, and colorectal cancer."

This sounds quite dishonest if what mark_l_watson said indeed holds. You could then equally say:

"When it comes to #1 health risk facing Tarahumara men, Americans are practically immortal: almost all their babies survive."