According to a report by PEOPLE, Rebel's weight loss is a result of the Mayr Method, based on the “Mayr Cure,” created by Dr. Franz Xaver Mayr nearly 100 years ago.
Using this method, clients aim to eliminate snacking, reduce gluten and dairy intake and change how they chew their food.
“She exercises with a personal trainer up to six times a week, goes on walks and is trying to up her protein intake nutritionally,” a source close to the Hollywood star told the publication.
“I know she's also been working on conquering her emotional eating patterns of behaviour.”
Back in May, Rebel revealed that she's "working hard" to achieve both her fitness and career goals, explaining that she's trying to get down to 75kg.
"Even if you have to crawl towards your goals, keep going, it will be worth it," she wrote in a motivating message on Instagram.
"Try and give a little bit of effort each day...I know some days are frustrating as hell, you feel like giving up, you get annoyed at the lack of progress...but good things are coming your way.
"What are your goals this year? I’ll be honest with you guys - with my 'Year of Health' mission I’m trying to get to 75kgs and career wise am trying to get one of my movies into production before the end of the year! Both of these things are requiring a daily effort and there’s constant set backs - but I’m working hard," she added.
Rebel spoke about how she lost a surprise amount of weight when filming the film adaptation of the musical Cats.
“I lost 8 pounds (3.6kg), shooting my number, in four days,” she told Entertainment Tonight.
“One, because there's a lot of physicalities… but also, they heated up the set very high, to almost 100 [degrees] Fahrenheit (37 degrees centigrade), so that we could never cool down.”
