Simple answer? nature will always adapt. yes we will adapt to the highly refined diet but if you think we are not adapting at the moment very well to this diet and we are talking the best part of 4-500 years since sugar as in the stuff in a bag first hit the diet.
if we still havn't full adapted to refined sugar after half a millenia then i don't see us evolving to the modern diet this side of the year 3000, but by then no doubt some wonderful on demand internal body nuclear power implant will take over from food.
To infinity and beyond!