Real food.  No grains. No legumes.  No dairy (except butter, of course)!

The basic idea is to eat like a caveman. Now, please do not take this too literally. I know there is no wooly mammoth meat at Whole Foods... But eat the types of foods that would have been around in pre-agricultural times. Think meat, fish, eggs, vegetables, nuts, seasonal fruit... Paleo is in many ways the most restrictive of the vintage diets. If you don't love cheese and cream, Paleo might be for you. (Most versions of the Paleo diet permit grassfed butter.) There are at least a couple of million Paleo eaters in the US, so there are lots of books, recipes, products, and services to help you find your way.