The ketogenic diet mainly comprises fatty foods like fish, cheese, nuts, and avocado, as well as low-carbohydrate vegetables, such as zucchinis and cucumbers. Fruit, with its high fructose content, is eaten less often. 

The rules are: 80 to 85% fat, 10 to 15% protein, and about 5% carbohydrates.

The German Nutrition Society, on the other hand, recommends: 55% carbohydrates, 30% fat, and 15% protein.

Normally, our body gets most of its energy from carbohydrates. It breaks them down into glucose, our main source of energy.

Excess glucose is converted and stored in the liver and muscles as glycogen. If there is too much glucose in the body, the sugar is converted and stored as fat. Most of those fat deposits form on the belly.

A cure for diseases?

The body adapts if a person leaves out carbohydrates and instead eats lots of fatty foods. First, it taps into its stores in the liver and muscles. Once these stores are used up, after a few days, the body goes into "ketosis," a metabolic process whereby the body burns fat for energy instead of carbohydrates.

These breakdown products of the fat metabolism now provide the necessary energy. The body burns fat and fat deposits melt away.

While some believe that the diet can help cure diseases like cancer, there are no reliable scientific studies to back that up. But research suggests that the ketogenic diet can have a positive effect on some disorders, like congenital metabolic disorders or childhood epilepsy.