Man's evolutionary history goes back 1MM years or so. He was a "hunter-gatherer". Ate what he found and what he killed.
That included meat, tubers, fruits and vegetables. (Did not include wheat, corn, soy "processed products".)
Only for the last 5,000 years or so has man fed significantly upon grains of any kind... that's not enough time for the genetics of our metabolism to evolve into readily accommodating a significant amount of grains in our diet.
Bottom line... "Eat what hunter-gatherer man would have eaten". Avoid other, and you will be healthier.