Dr. Oz's 'Miracle' Diet Pills: 5 Controversial Supplements
Dr. Oz testifies in a Senate hearing about promoting untested weight loss supplements.
Credit: Senate.gov

This week, Dr. Mehmet Oz, host of "The Dr. Oz Show," sat down to explain to senators why he, as a surgeon and popular doctor, promotes what some experts have called unscientific claims about "magical" weight-loss products on his show.

Sen. Claire McCaskill, D-Mo. — chairwoman of the U.S. Senate Committee on Commerce, Science and Transportation's Subcommittee on Consumer Protection, Product Safety and Insurance — led a panel on Tuesday (June 17) that targeted weight-loss diet products that their manufacturers claim will help consumers burn fat but have little or no reputable scientific data to support such claims.

"I don't get why you need to say this stuff, because you know it's not true," McCaskill told Oz.

On his show, Oz has called some herbal weight-loss products the "magic weight-loss cure" and "the No. 1 miracle in a bottle." Once these products are mentioned on the show, they can sell out instantly — a phenomenon known as the "the Oz effect."

However, Oz said he uses "flowery language" to give his audience a little nudge of hope and motivation to lose weight, because they already know that adjusting diet and exercising are the things they need to do. [10 Fitness Apps: Which Is Best for Your Personality?]

He added that he personally believes in the products he promotes, even though scientifically, they might not hold up.

"I actually do personally believe in the items I talk about on the show. I passionately study them. I recognize that, oftentimes, they don't have the scientific muster to present as fact. Nevertheless, I would give my audience the same advice I give my family, and I have given my family these products," Oz said.

Here is a look at some of the supposedly metabolism-boosting, weight-loss supplements Oz has endorsed, for which there's scarce scientific data:

Green coffee bean extract: Perhaps the most well-known weight-loss supplement that Oz has popularized is green coffee bean extract, whose major ingredients are chlorogenic acids. "You may think magic is make-believe, but this little bean has scientists saying they've found the magic weight-loss cure for every body type. It's green coffee extract," Oz said about the supplement during an episode that aired in 2012.

Testifying in front of the panel, Oz defended his endorsement of green coffee beans by citing a study that found people who took the supplements did lose weight. However, that study was funded by the product's manufacturer, McCaskill noted.

These purported weight-loss supplements could even be harmful, recent research suggests. A study in mice, published last year in the Journal of Agricultural and Food Chemistry, found that chlorogenic acid in green coffee bean extract didn't help prevent weight gain in mice fed a high-fat diet and was linked to an unhealthy buildup of fat in the liver.

Raspberry ketone: Oz has called raspberry ketones "the No. 1 miracle" fat-burner. This compound found in raspberries has been tested in animals and in cells in the lab, but never for weight loss in humans. Some research in animals has suggested that it might increase some measures of metabolism. Still, there is no reliable scientific proof that it improves weight loss in people, and no study has examined its safety and dosage.

Garcinia cambogia extract: Garcinia cambogia is a small, tasty fruit native to Southeast Asia, and was featured in Oz's "The Newest, Fastest Fat Busters" episode. The extract contains a compound called hydroxycitric acid (HCA) that is touted for weight loss, but studies have produced mixed results. One study, a randomized controlled trial published in The Journal of the American Medical Association in 1998, even found that people who took the supplement as part of their weight-loss diet lost less weight than the control group who took a placebo.

African mango diet pill: Irvingia, or African mango extract, is another product touted for weight loss that Oz has talked about on his show. In a 2013 review of studies, published in the Journal of Dietary Supplements, the researchers concluded that the effects of this supplement on body weight and related outcomes were unproven, and therefore, they said, the supplement could not be recommended as a weight-loss aid.

Saffron extract: This expensive, exotic spice that is frequently used in Middle Eastern cooking has much folklore describing its ability to lighten up mood, but modern science hasn't found it is a "miracle appetite suppressant" as Oz has claimed. No independent studies of the supplement have found that it helps people lose weight. 

Email Bahar Gholipour. Follow us @LiveScience, Facebook & Google+. Original article on Live Science.