Back in the mists of time (the 80s/90s when I was younger) it was really "in" to detox with 48 hours of fruit (especially grapes) salad (no dressings or cheeses ) and mineral water.
After, you emerged revitalised and clean skinned (ha! the reality was spots and the runs and in my experience a headache after no coffee)
Plus it was knackering .
Mainly to kick start good eating habits . TBH anything would be nectar after that, even poached eggs and toat.