I'm a big fan of Bulletproof Coffee. I drank it as part of the intermittent fasting diet and lost a stone in a month! Basically you drink a cup instead of having breakfast, and then you only eat between 2pm and 8pm. The fasting aspect means your body stays in a fat burning state so the results are speedy.
I did eat well during this time (so a diet high in vegetables, protein and good carbs e.g. sweet potato) and would have lost weight as a result regardless, but drinking the coffee definitely sped up the process.
I would say I normally lose a pound a week if I eat a clean diet like this (slow and steady), but with Bulletproof Coffee I would lose around three pounds a week quite easily. Definitely try the branded version though as it's the Upgraded Octane Oil that worked for me - not the coconut oil copycat
You can get the Upgraded Octane Oil and coffee on uk.bulletproof.com/ . The grass fed, unsalted butter is available in most supermarkets. I get mine from Waitrose - either Kerrygold or Yeo Valley taste good!