I just completed the 3 day detox plan that comes with the smoothie diet and feel a lot better than when I started.
The first day was the hardest for me, mainly because of the cravings. By the end of the second day I felt a lot better and wasn't craving anything sugary - like I'm used to.
Just a quick heads up, you will be visiting the toilet often, so be prepared. As for weight loss, I did lose 2 pounds in the 3 days, but to be honest, I did it mostly to try and break the snacking phase I was going through, and it did help.
I think you will do great with your 3 day juice fast, just ensure you follow a structured plan with detailed recipes like the one I got with the smoothie diet plan. You can find out more about it here
https://smoothielover.net/smoothie-diet-review/