(NEWSER) – Milk in your coffee not cutting it? Perhaps you'd like to drop a pat of butter and some coconut oil in instead. Oh, and don't forget the eggs. The ingredients are all part of a new trend in coffee drinking, apparently driven in the US by health entrepreneur Dave Asprey. He's all about improving physical and mental performance, becoming what he calls "Bulletproof." The idea for Bulletproof coffee—packed with butter and coconut oil—came from tea made with yak butter in Tibet, he explains.