Drugs and whiskey were once mainstays of the rock 'n' roll diet -- but Grammy-winning R&B crooner Usher credits his "killer cut" to colonics.

"Janet Jackson told me to do it," he says on VH1's Rock Bodies, airing tonight at 9. 

"I'm not too fond of having the stuff sucked out of me and a tube up my butt, but I've done it a couple of times to clean my body out. I hate it, but it's healthy for me." 

After seeing the VH1 special, you may never look at some of your favorite singers the same way again. 

Many a pop star's medicine cabinet is filled with over-the-counter weight-loss aids, including Xenadrine RFA-1, which contains ephedra and has been blamed for 80 deaths. 

Others beg their doctors for Xenical, a prescription pill that reduces the body's absorption of fat. 

It also may produce urgent bowel movements, which could cause embarrassing situations. 

Extreme diets landed Anastacia in the hospital for a long and painful recovery. 

The pop star, who was diagnosed with Crohn's disease at age 13 and now bears a scar from intestinal surgery, turned to fads when her record label urged the once-chubby singer to lose weight, she told VH1. 

Now she says, "I'd rather be a chunky singer than a really unhealthy girl . . . and if I get chunky that might be funky." 

Her new diet: salsa, re-fried beans and Doritos. 

She has no problems with Botox, however, calling it "a really interesting way of hiding lines that start to exist for anyone." 

Cher has a secret too. 

If she has a concert tour or a photo shoot, she makes daily appointments with Utta, an L.A. massage therapist known to have "hands of steel." 

By kneading, pinching and stretching the skin, Utta supposedly stretches the fat away, so Cher claims her skin looks smooth and cellulite disappears. 

Of course, some musicians stay in shape the old-fashioned way. 

Janet Jackson pursues a grueling ab workout, and when he's not hooked up to a vacuum tube, Usher sticks to a strict diet of fish, chicken and vegetables, he tells VH1. 

Sheryl Crow keeps trim by running, rock-climbing and canoeing. 

It all comes down to "what's inside," she says on the show -- or for some stars, what isn't.

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