I’m not a doctor… but have studied nutrition and read a lot on health/fitness… plus i have my own experiences, observations…
I m not sure you could continue on fruit/veg for very long, especially if you deprive yourself - only give yourself 2 servings a day. This may work for 1 or 2 days but then you would get weak &/or worse, esp if you have work to do, running around to get done…
I have been on liquid fasts and they seem to work fairly well, if at least some of the liquid has calories & fat in it… like espresso with cream/honey…

That is waht i drink… not saying it is perfect, but gives me energy and keeps me feeling OK…(Caffeine is an anti-depressant, though not sure if it is officially…). Liquids are easily digested/processed by the body, giving the body the energy it needs and no excess… to turn into fat.
When the body digests food, it needs energy to do that. Digestion is very complicated, involves all the organs of the body… So when you eat just veg, for example… well, the stomach juices and various hormones used in digestion (bile, etc) are made of fat and protein and you use all that up… and it is not good for the body to do that often… (eat veg w/o protein/fat)… I tend to think this should NEVER be done…
One time i didn’t eat much all day and at the end of the day, ate a carrot. I got a headache and felt terrible… will never do tht again…
I have heard a raw milk -only diet is good… but havne’t tried it for more than 1/2 a day… i am thinking of doing so… (though it should not be store-bought milk, which is not healthy… plugs your arteries) Again, i like the one where you do nothing but liquids… it gives the body a break… etc… (There are dairies where you can get sterile raw milk… i had to go through internet to find one in my area…).
I havne’t eaten anything today except Jesus

and i feel really good…although i do need to eat soon…i can feel it.
I feel closer to God when i fast… way!! i guess that’s why wer’e supposed to do it…
I think everyone should fast at least once a week… i know a man who did that and he lived to be 100…
God bless…