I have seen the same commercial. Dunno if the guy lost the weight or not, but really don't care, to be quite honest. When I was wrestling in high school I had to drop a weight class in two days. I lost 18 lbs from Thursday night to Saturday morning and was still functioning, but only barely. Won my first match then quickly dropped the next two due to lack of energy no matter how many oranges and how much honey I took in.
It is not even close to healthy and 20 lbs in 24 hours would leave you with no energy, no fluids and possibly no life. Gramm is right, 19 lbs of that was probably water weight and the other 1 lb was brain matter.