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I think 20 lbs is a bit optimistic for 22 days. Might be possible if you have plenty of lean body mass and an active job.
I’m assuming you want to enjoy Christmas food and drink? A 22 day fast is going to require at least a few days of refeeding before eating normally again.
You could still lose a significant amount with intermittent fasting, OMAD (one meal a day), or rolling 48’s/72’s.
A lb of fat is around 3500 calories. So if you are in fat burning mode ( low insulin resistance) if you burn around 3500 calories a day on a water only fast, you can expect to lose 1 lb a day. If your insulin sensitivity is lower like most people, your weight loss will be lesser as the body will lower metabolism. Hence fasting, and not merely calorie deficit, is critical to weight loss as fasting improves insulin sensitivity ,which in turn makes body go into fat burning mode faster
20 lbs of fat loss in 22 days isn’t possible. But with water weight you might lose more than they typical 2 lbs a day - especially early on.
People doing OMAD often report losing 3-3.5 lbs a week initially. Rolling 48s or 72s might improve on that.