But the Bridesmaids star's weight loss journey hasn't been without struggle.
Rebel took to Instagram on Wednesday to share a throwback photo with tennis legend Novak Djokovic at a charity event, saying the picture was taken at the "unhealthiest" point of her life.
"[I was] overweight and indulging way too much with junk food. Using food to numb my emotions," she said.
"My father had passed away of a heart attack and it was such a sad time. I didn’t think highly of myself and wasn’t valuing myself how I should have.
"I look back now at that girl and am so proud of what she’s become and achieved."
Rebel encouraged her fans who are also struggling with weight issues and emotional eating to respect themselves and do what's best for them.
"I feel you. I know what it’s like. But it’s never too late to start improving yourself and trying to be the best version of YOU possible. It’s not a race and it’s not a competition," she said.
Rebel has been following the Mayr Method diet plan which involves eating high alkaline whole foods very slowly while aiming to chew each mouthful for 30 seconds.
"The goal was never to be skinny,” she said on an Instagram Live, explaining that her journey started when her doctor told her she'd have a better chance at freezing her eggs if she were healthier.
“It was never to fit into a certain dress size. I put in a goal weight in there because I needed some tangible thing."
Last year, Rebel revealed some of the nutrition and exercise tips that helped her overcome her relationship with eating and her body.
“It was the emotional stuff about realising why I was overeating, why I was emotionally eating and trying to solve that, that was the biggest lesson,” she said in an Instagram Live to fans.
“As all career women would know if that is something that interests you approaching 40 is a good time to do it. So I was thinking about fertility and thought I am going to do this and get healthy.”
The Pitch Perfect star has previously revealed she got treated differently when the kilos started to drop.
“Sometimes being bigger, people didn’t necessarily look twice at you. And now that I’m in a good shape, like, people offer to carry my groceries to the car and hold doors open for you," she told The Morning Crew's Hughsey, Ed and Erin.
"I was like, ‘Is this what other people experienced all the time?'”