Comment by woodandsteel

The basic principle is to avoid refined carbohydrates. If a food is unrefined, then it is ok, with the exception of potatoes, which have way too much carbohydrate.

A good book on this is The Instinct Diet by Susan Roberts, who is a well-known nutrition researcher.

The paleos say we should eat the same diet as our foraging ancestors. The problem with that is different foraging tribes had very different diets. However, one thing they all had in common is they didn't eat any refined carbohyrates. That leads to the possibility our bodies are not well adapted for them, and there is a great deal of research that is n fact the case.