'20/20' Investigates Diet Pill Ad's

April 23 -- Diet pill commercials often make it seem so easy to lose weight; an overweight person is shown photographed with their flab and then pictured with a new fit physique. How do they do it?

In a special report, 20/20 investigated such claims and found three common gimmicks used to play with the truth from manipulating photos and quoting experts who aren't what they seem to ads that hype up claims without valid scientific support.

Take this for example: in one ad for an old formula of Hydroxycut, Marla Duncan claims she lost 35 pounds. It was "so easy," she said. Missouri attorney general Jay Nixon found one very good reason why — when she took the before picture Duncan had recently been pregnant and given birth.

Is this just downright deceptive?

"We wouldn't be suing people if we didn't think that they were deceptive," Nixon told ABCNEWS.

Hydroxycut said many of their ads did disclose Duncan's recent pregnancy and said their pills are proven to work. But Nixon has his own view. "They care more about their bottom line than your waistline," he said. He is suing the company for misrepresentation, which they deny.

Bulking Up to Slim Down

There's nothing like gaining weight before going on a diet.

In 2001, Mike Piacentino was featured in before and after pictures for Xenadrine. He started out as a competitive bodybuilder, but Todd Macaluso, an attorney who is fighting Xenadrine's appeal of a case he brought over weight loss claims says Piacentino testified that the company paid him to eat.

"They gave him a food allowance and they said, you know, you've got to fatten up," said Macaluso. "Eat like a pig, gain as much weight as you can, stop working out."

Piacentino put on the pounds by skipping his workouts and then gorging on endless boxes of doughnuts and gallons of ice cream. Soon it was time to take the before picture.