Well, think of it this way.
When you do not eat that much, your body fat lowers little by little, but considering that this is a question, I'd say starvation. Think of it as when you fast (Not eating all night say to go to a doctors appointment) your body stores the fatty acids to make ketone! The ketone will build a bloodstream that flows to the brain and other parts of the body!
To sum it up, starvation.
