The ketogenic diet began life as a treatment for epilepsy and seizures in children. It’s come into vogue in recent years among adults without seizure conditions to lose weight.
The body mostly burns carbohydrates, in the form of sugars, as its fuel. When your body is deprived of sugar, it will look for whatever other fuel it can find. Much like a person with poor meal planning habits reaching for a can of black beans on the back of the shelf and hoping to God for the best, the body burns reserves of fat in place of sugar when it has nothing else to turn to.