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Stars live under a microscope in the spotlight and are constantly criticized for their weight, so it's no wonder that some of them decide to shave a few pounds off -- be it for health benefits, in preparation for swimsuit season or any other reason.

Here's a look at seven shocking celebrity weight loss transformations:

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Adele

The "Hello" singer has made headlines recently for showing off her dramatic transformation after she reportedly said she knew "she had to change something."

A source told People that Adele's weight loss was inspired by her desire to be "the healthiest mom possible."

Photos of Adele's transformation have made their way online on various occasions, flaunting a slimmer figure at Drake's birthday party in October 2019 and at a Christmas party later in the year.

Fans got their best look at the singer's transformation in a recent photo she shared to Instagram in celebration of her 32nd birthday, posing in a slim black dress that cut off mid-thigh.

While spotted on vacation, Adele reportedly told fans that she'd lost 100 pounds, and her former trainer recently explained that the weight loss "was about getting her healthy" rather than the publicity stunt she was accused of orchestrating as her album is rumored to drop this year.

Looks like the Grammy winner is saying "hello" to a whole new lifestyle.

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Rebel Wilson

Rebel Wilson, star of "Pitch Perfect," is beginning to look fit perfect these days.

After declaring 2020 her "year of health," the 39-year-old actress began a health and diet regimen that's provided great results.

Wilson shared a photo of herself at the beginning of the year on the beach, just as she was beginning her weight loss journey.

Wilson said she's "deliberately hydrating" and "trying to avoid the sugar and junk food."

A few weeks later, Wilson's trainer shared a photo of the actress in all black athleticwear, as well as a video of her training with CrossFit ropes.

Wilson's trainer, Jono Castano, revealed that she's been working out seven days a week, and it's definitely showing.

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Jillian Michaels

Jillian Michaels is best known for whipping people into shape on "The Biggest Loser," but she first had to whip herself into shape.

The fitness guru recently took to Instagram to share a throwback photo, revealing her former weight.

"Here's me at 5'0 tall and 175 lbs," she wrote in the caption. "If I can do it - anyone can. Share your story..."

Of course, the 45-year-old trainer has slimmed down over the years, and is now an advocate for health and wellness.

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Jonah Hill

Jonah Hill was always known as the chubby, funny guy, but in recent years, he's proven that's not always the case -- on screen and off.

Jonah Hill in 2015. (Photo by Raymond Hall/GC Images via Getty)

Jonah Hill in 2015. (Photo by Raymond Hall/GC Images via Getty)

Hill started dropping weight between 2015 and 2016 and has continued to trim down since.

Jonah Hill in 2019. (Photo by Gotham/GC Images via Getty)

Jonah Hill in 2019. (Photo by Gotham/GC Images via Getty)

The 36-year-old actor is almost unrecognizable compared to his former self.

Hill revealed on "The Tonight Show" in 2016 that he turned to "21 Jump Street" co-star Channing Tatum for fitness tips, who simply recommended he eat healthier.

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Christina Aguilera

Christina Aguilera, 39, burst onto the music scene when she was around 20 years old, and since then she's received a great deal of criticism for her weight.

Her weight has fluctuated over the years, rising and falling after the 2008 birth of her son Max.

Christina Aguilera performs onstage at the 2011 American Music Awards. (Photo by Kevork Djansezian/Getty Images)

Christina Aguilera performs onstage at the 2011 American Music Awards. (Photo by Kevork Djansezian/Getty Images)

However, in 2013, Christina Aguilera turned heads at the American Music Awards for her dramatic weight loss.

Christina Aguilera at the 2013 American Music Awards. (Photo by Kurt Krieger/Corbis via Getty Images)

Christina Aguilera at the 2013 American Music Awards. (Photo by Kurt Krieger/Corbis via Getty Images)

When asked about her weight loss secret, Xtina told E! News: “Laughter, happiness, breathing and I did some yoga.”

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Ethan Suplee

Ethan Suplee is feeling proud these days.

The 43-year-old actor dropped jaws recently after revealing his impressive weight loss.

Ethan Suplee in 2002. (Photo by SGranitz/WireImage)

Ethan Suplee in 2002. (Photo by SGranitz/WireImage)

You may remember Suplee as Louie in "Remember the Titans," but you probably wouldn't recognize him today.

The actor took to Instagram to show off his progress.

"This may be my favorite moment of the year in the gym, because it's empty," he captioned a Jan. 1 photo. "2020 goal: all the abs. What are yours?"

Honestly, it's a bit hard to believe he even needs to set fitness goals anymore.

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Khloe Kardashian

Khloe Kardashian is another star who has grown up in the spotlight, but being in a family full of models meant that her weight drew extra criticism.

Kardashian began to work out to cope with the beginning of her lengthy divorce from Lamar Odom.

TV personality Khloe Kardashian in 2012. (Photo by Barry King/FilmMagic via Getty)

TV personality Khloe Kardashian in 2012. (Photo by Barry King/FilmMagic via Getty)

It wasn't long before the reality star began noticing a difference and pushed on, making a surprising transformation.

Khloe Kardashian in 2015. (Photo by Daniel Knighton/FilmMagic via Getty)

Khloe Kardashian in 2015. (Photo by Daniel Knighton/FilmMagic via Getty)

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Kardashian, 35, would even go on to host a weight loss show called "Revenge Body," though the program and other weight loss products she's promoted have drawn criticism.