What is the Ketogenic Diet and What Foods are Acceptable?

The ketogenic diet is a low carbohydrate (carb) diet designed to change the energy source of the brain from sugar to fats (ketones) and to increase the use of fats as an energy source in the body as a whole by severely restricting the intake of dietary carbohydrates. It overlaps a lot with the Paleo diet in that the ketogenic diet consists largely of meats and fats.

For the ketogenic diet, fish are good choices. Full-fat dairy is allowed, but fermented and unsweetened ones are preferred. Fruits are quite limited though, to small amounts of berries, plus lemons and limes in moderation, and olives and avocado (these two are fatty fruits, rather than sugary). Vegetables consist mostly of non-root ones because those have more carbs. Legumes are largely avoided, except small amounts of green beans and peas.  Nuts and seeds are used in moderation as they have some carbs; but avoid peanuts, which are legumes, not nuts. 

Fats represent most calories in the ketogenic diet: avocado oil, coconut oil, olive oil, butter, cocoa butter, MCT oil, and nut oils in moderation (i.e. walnut, sesame). Eggs and unsweetened gelatin are fine. Processed foods and condiments that have added sugars or carbohydrates should be avoided. Sugar alcohols are also avoided; stevia is acceptable, but watch for added carbohydrates in some stevia products.

Unsweetened whey protein isolate (not concentrate) has the least amount of lactose of the milk proteins; unsweetened egg white protein is also fine. Though legumes are avoided if they have carbs, unsweetened pea protein or soy protein isolates are acceptable options in the ketogenic diet.