A keto diet is well known for being a low carb diet, where the body produces ketones in the liver to be used as energy. (ruled.me)
When this happens, your body becomes highly efficient at burning fat for energy, while also turning fat into ketones in the liver, which can supply energy for the brain. (fitnessandpower.com)
While we are in this state, the production of ketones in the liver is triggered that has the ability to break down fats. (lowcarbalpha.com)