A question with a lot of answers, but for the individual we can say what is not food to start with. I do not have an issue of eating stuff that I do not consider food. It is just a matter of reminding myself what are and are not foods, until it becomes habit.
Short list of non-foods: Sugar, wheat, omega 6 oils, many grains, exorphins, anything containing hormones, flavour enhancers, GMO's, and other stuff.
Long list of proper foods: Meats, fish, and roots, stems, and leaves, blooms, in there cooked or raw form. Take it easy on seeds, for they carry much energy.
The thinking that these are or are not foods must come first, and control / influence the action. Sharma does not agree, but that is his problem.
But what do I know?