Rihanna apparently believes she has to be a "perfect physical specimen" in order to keep Chris Brown interested.
The gorgeous star has had a tumultuous relationship with Chris, which resulted in him assaulting her in 2009.
Since then the couple has been notoriously on and off, and friends are now claiming the 24-year-old would do anything to be with Chris - including changing her body.
"Rihanna thinks that if she makes herself the perfect physical specimen, Chris will be hers forever," a source told British magazine Heat.
Another source added: "The problem is that Ri-Ri is constantly dieting and counting calories, but she still wants to have curves for Chris. I think Chris has made her quite self-conscious about the fact that her boobs and much of her famous booty have gone, as she's lost weight recently and she feels bad about losing her curves."
The gorgeous star cut a striking figure on the front of GQ magazine earlier this month, posing with just a leather coat covering her modesty.
Friends say she wasn't happy with the stunning shot and worried she didn't look as good as Chris' curvier ex Karrueche Tran.
Chris and Karrueche recently split after he publically admitted he was still in love with the Diamonds singer.
"Ri-Ri hoped that posing naked in GQ would make her feel sexier, but she just critiqued herself mercilessly," an insider said.
"Chris compares her with Karrueche, and she just feels like she's coming up short. She tried butt-lifting exercises, but they actually made her bum smaller...She knows he's a butt guy and she has been obsessing about making it bigger since they started dating again."
Despite her supposed body issues, the star has been looking gorgeous as ever recently.
Yesterday she stunned in two different outfits as she switched on the Christmas lights at a London shopping centre and later performed an exclusive concert for 20,000 UK fans as part of her 777 tour.
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