Bulletproof Coffee: What Is It, How It Works, & Side Effects! Learn everything about this viral weight loss drink before making it a part of your routine :) Bulletproof coffee is a coffee made by mixing coffee, butter or coconut oil in hot water. Bulletproof coffee works by pushing the body into the fat burning mode.It occurs when you have restricted consuming carbs long enough, and your carb or glucose reserves are empty! Basically works well with a keto or low carb diet.. And you must not use