"Eat food, mostly greens, not too much" -Michael Pollan
Go to the supermarket and only buy things with one ingredient, cook and eat those things.
What qualifies? Vegetables, fruit, rice, beans, meat, etc.
ONE ingredient only.
(Technically raw sugar or lard qualify to be on my list, but I think most people who passed high school know those aren't food)
EDIT: well, yes raw sugar and lard are food, what I meant was you shouldn't be eating either in large quantities.