The fat burning smoothie tastes bitter. Is it the grapefruit?

Chances are it's the green tea ... not the grapefruit. Green tea leaves are very delicate so if you steep them for too long or in water that's too hot, you'll get a bitter tasting result. Steep your green tea in water that's just below boiling temp and steep it for 5 minutes max. That should do the trick!

Another option would be matcha green tea powder. Sub cold, filtered water for the tea and add one serving of matcha powder. We also have a tasty matcha smoothie recipe you might like.