Bulletproof coffee is a great breakfast (and snack) for anybody on a high fat diet like keto or Atkins. This is because while on these diets, your body has put itself in a state where it can more easily convert fat to energy. However, people on a regular high carb diet will not be able to make the most of all that fat and will just be hungry and tired after an hour.

Don't get me wrong, I think most people need more good fat in their diet. But if you're on a "regular" diet, the fat needs to be a supplement, not a replacement.