That person seemingly turned his health around from 456 lbs to 180 lbs. But he died at age 50. I am scared of fasting because I dont think there are enough studies on humans to understand the long term effects like gallstones and lean tissue loss, especially heart muscle.
He represents such an extreme case, it is hard for me to draw any broad conclusions from his life. The man never had a healthy relationship with food.
1lb of body fat is ~3500 calories. An average person doing average things burns around 2000 calories. You can easily put in your own numbers and get your own results. Just calculate your TDEE(total daily energy expenditure) and look up how many calories in a pound of fat to whatever tolerance you want.