[thoughtexprmnt]

I think just making any significant change to one's diet can, in the short term anyway, have noticable positive effects, especially depending on what the previous diet looked like. But over time those effects tend to level off and eventually into net-negative consequences from whatever's being restricted out. I can definitely see that being the case for a prolonged potato only diet.

I also think the best long term strategy is to focus first on eating plenty of nutrient dense, minimally processed foods which will naturally tend to crowd out the junk. Junk being anything consisting mostly of the cheap subsidized ingredients like wheat, corn, and soy.