Around twelve hours after your last consumption of food, the body begins to break fatty acids down into ketone bodies, which will become the new blood-borne chemical energy vector, replacing the glucose that your body is running out of. 102 While we would expect this metabolic switch to be “flipped” at the twelve-hour mark and the transition to ketosis to be initiated at that time, it may take a much longer fast of perhaps seventy-two hours for some individuals to transition completely to a ketogenic state.103
