Agree with PP - it is possible to see such a dramatic shift in the scales, but alot is water related and reflects how radically you alter your diet and lifestyle.
Funnily enough on March 8th I stood on my scales after a long period, including lockdowns of being extremely unhealthy, and tipped over the 14 stone mark to 14 - 2. Enough was enough. My "fighting weight" was always between 9 and 10 stone and I'd been denial about the creep due to alcohol consumption, takeaways etc, and at 52 was in denial about my fast and furious menopause with all the implications of that.
So I did a three day water fast, and since then have been eating one meal a day, early evening, ketogenic so meat, fish egg dishes with permitted veggies, and in the first week I was down ten pounds. Also no alcohol and no wheat or dairy as I suspect I'm a bit intolerant (IBS since 25). So yeas, lots of water weight.
It's slowed / stalled since then, but I feel so much better overall I don't really mind if it's a gradual process now - today at end of fourth week, I'm solidly at 13 - 2 after going up and down between that and 13-7.
I'm not saying this would work for everyone, but I'm a creature of extremes so don't come for me and I'm fortunate to have no risky underlying health issues.
So yes, it can be done depending on how restricted the diet is.