The 32-year-old singer recently admitted to packing on the pounds while pregnant with her baby daughter Maxwell because she wanted to enjoy her first pregnancy, reported Contactmusic.
"The easiest way to get motivated is to strip naked and look in the mirror. It's not fun to be talked about. It's not fun to be judged," she said.
But despite her slim down, Simpson said that attending the weekly WeightWatchers meetings to track her progress was a daunting task.
"The very first time I got on the scale in my WeightWatchers meeting, my heart was pounding because I had no idea how much I weighed. I was always the girl who stood on the scale backwards because I didn't want to face it."