The Incredible Shrinking Woman! Christina Aguilera Shows Off Hot New Body After 55-LB Weight Loss -- How'd She Do It?

Monday night on The Voice, it was all about The Body -- Christina Aguilera's to be exact. The pop superstar and judge on the show flaunted a seriously slim new frame during a performance of "Feeling Good" with rapper Flo Rida, and an expert tells RadarOnline.com that she's dropped more than 50 pounds!

"We're finally reminded of what a small frame she actually has!" celebrity weight loss coach Alicia Hunter tells RadarOnline.com exclusively.

Only a few years ago, at the Michael Jackson Tribute Concert in 2011, the 5'1" diva "looked to be topping the scales at a whopping 165 pounds," Hunter, author of The Accidental Diet: From Fugly to Fox, says. "It was widely reported that relationship problems, combined with her new gig on The Voice were to blame for her dramatic weight gain."

Still, Aguilera refused to put away the bodysuits, insisting, "Actually, the challenge I've always had is being too thin, so I love that now I have a booty, and obviously I love showing my cleavage. Hey, if you can work it and you can own it, that confidence is going to shine through."

But soon, she started to shrink. During a performance on The Voice last year, Aguilera was noticeably smaller.

"Christina was still a far cry from her 'Dirrrty' days, but she was definitely making an effort to drop all the excess weight," Hunter says. "She looked to have dropped at least 25 pounds and was hovering around 140."

Now, Hunter says, "She looks to be clocking in at around 110 pounds tops, maybe even lower since she looks to be lacking healthy muscle tone!"

"She looks drawn, and it appears that she may have dropped the dramatic amount of weight through less-than-healthy means," Hunter claims. "Her arms and legs don't look especially toned, and the fact that she shrunk pretty rapidly is indicative of a crash diet of sorts."

"She may be dabbling with the HCG diet, which is very restrictive, consisting of only about 500 calories a day and injections for appetite suppression," Hunter says. "Or Atkins taken to an extreme, or even straight-up appetite suppressants to kill any desire for food."