The ketogenic diet is a high-fat, moderate-protein and very low-carbohydrate diet. Carbohydrates are the body's preferred source of energy, but on a strict ketogenic diet, less than 5 percent of energy intake is from carbohydrates. The reduction of carbohydrates puts the body into a metabolic state called ketosis. Ketosis is when the body starts breaking down stored fat into molecules called ketone bodies to use for energy, in the absence of circulating blood sugar from food. Once the body reaches ketosis, most cells will use ketone bodies to generate energy until you start eating carbohydrates again.