Here are the links that explain how this is supposed to work.
First, how/where he came up with the idea and his recipe:
» Recipe: How to Make Your Coffee Bulletproof…And Your Morning Too The Bulletproof Executive
Second, bulletproof fasting as part of his body hacking (sorry, the proper term is "biohacking") stuff:
» Introducing Bulletproof Intermittent Fasting: How to Lose Fat, Build Muscle, Stay Focused & Feel Great The Bulletproof Executive
Female, 5'3", 49, Starting weight: 163lbs. Current weight: 135 (more or less).
I can squat 180lbs, press 72.5lbs and deadlift 185lbs