title_body: What is the science (if any) behind bulletproof coffee?
upvoted_answer: Another view on this:
  
  Bulletproof coffee is often used with a low-carb diet, often referred to as the "keto diet", which has some similarities with Paleo, but is quite different. The diet requires you to cut out as many carbohydrates as possible out of your diet in order to get your body into a state of ketosis, where most of the energy in the body is produced by processing fat instead of carbohydrates.
  
  When following the keto diet, you need to eat a lot of fat, minimum carbohydrates and a reasonable amount of protein. The goal is to get most of your calories from fat. Getting in all the fat that is required is often difficult, so in that context, bulletproof coffee is nothing more than a delivery method for fat. There's nothing special about it, it's just easier to drink a spoonful of butter melted in coffee than eating it on its own.
  
  If you want to read up on keto further, the keto reddit has lots of resources on it: Keto In A Nutshell.