Many of the celebrities on this list lost weight through healthy eating and exercising, some through fad diets and others ate melted Haagan Dazs to gain weight.
Check out gallery of the most incredible celebrity body transformations
#1 Jessica Simpson
The singer and clothing mogul gained 70 pounds during her pregnancy with first daughter, Maxwell. She eventually slimmed down, attributing her weight loss to eating healthy and working out three days a week with a trainer and doing cardio on her own twice a week.
#2 Kelly Clarkson
Kelly first gained about 30 pounds in 2007, which she lost in 2012, only to gain it again after having her first child.