‘Bulletproof coffee’ is said to help aid weight loss and boost metabolism. The high-fat, low-carb drink is a controversial mix but Mirror writer Niamh Kirk braved a taste after digging into the science behind it’Bulletproof coffee’ is said to help aid weight loss and boost metabolism. The high-fat, low-carb drink is a controversial mix but Mirror writer Niamh Kirk braved a taste after digging into the science behind it