It's called the paleo or caveman diet. I can't remember now if this is one I actually tried or not. It's a tougher one to do, too, since I think there's more restrictions.
Oh, well, I guess it's actually closer to keto than I thought. Grains aren't allowed, so my oatmeal is a fail, but the apple, pecans and egg all work. :)
Here's a link to the ultimate paleo guide website if you want to do some reading. :) You can scroll down a little to see the list of foods that are allowed.
RE: Grandpa Gotta Eat—Oatmeal and Fried Egg