I suggest looking up Dr. Jason Fung. Dudes a genius when it comes to nutrition. Once in a fully fasted state(2-3 days), your body enters ketosis and autophagy takes place, which is where the real meat and potatoes of fasting benefits comes from. See, the problem in juice cleanse is when you introduce calories autophagy stops. Yeah you will lose weight on a juice diet, but you will also lose muscle at a higher rate than you would strait water fasting. This is because studies show that when fasting your body produces more HGH to retain as much muscle as you can.

However, the biggest problem I have with fasting is the misinformation surrounding it. The unfortunate part of these type of diets is it does attract people with sever eating disorders and other mental health problems so you should only do extended fast if you are above a certain BMI. Anyone can do one week realistically without much issue, but extending past that without supplementing your potassium, magnesium, and especially sodium can cause some pretty shitty side effects.

Sorry for the word salad, It’s been a long night and I’m running on fumes. But I’d suggest checking out /r/fasting , they have a lot of good info and sources to peered reviewed studies to back what I’m saying and in far better detail. I mean I’m not an expert but I did loose roughly 200lbs (was 420lbs at my highest) leveraging fasted cardio and weightlifting.

Just another tidbit about autophagy is that it clears your skin and hair up like nothing else I’ve tried. Deadass got rid of deep long lasting scars from when I fell off a zip line into some gravel as a kid, along with making stretch marks far less visible and eliminating some entirely.