I think just eating soup every day would get very boring and therefore you would be likely to fail/fall off the wagon. It is also quite difficult to get enough calories in eating just soup (unless they are creamy ones).
What you could do is 5:2 or 4:3 and just eat soup on the 2 (or 3) days and eat normally on the other days.
I'm going to go against everyone else here and say 'why not?'. Not for long obviously, and maybe with added protein (bit of fish or chicken breast maybe), or some cheese, but if it motivates you to get going, then do it.
There is something depressing about salad at this time or year, but when it is whizzed up into a warm soup, the world seems a better place .
i do this alot, get fed up and my fave is a homemade concoction of
carrots, onion, broccoli, sweated down, a bit of green pepper. bung in loads of garlic, fresh ginger, garam masalla and a little cumin. chuck some red lentils in, water, salt pepper. simmer for about an hour.
blitz. lovely thick dahl type soup. very filling! oh and a little tin of toms. lasts me a few days.
I do this, have been doing alternate day fasting where every other day i can have 500 cals. On those days i eat soup for lunch and dinner. The other days are normal, sensible eating (with treats at weekends). Have lost 10lb in 5 weeks and it's really sustainable!