Fasting is a funny thing, because the definition is highly variable. As a teenager I fasted a few times[0] while doing construction work —- mostly carpentry. How the hell does a 17 yr old get the energy to move lumber, swing a hammer, etc while fasting? The answer is liquid calories. Juice fasts feel the same to me, I’m going to guess that someone could easily gain weight on a juice “fast” if they drink enough.

0 - religion causes you to do strange things sometimes.