Dr. Mehmet Oz became a celebrity thanks to Oprah, and parlayed that into a popular daily television show, newspaper and magazine columns, and several best-selling books. The problem is that a lot of what he says is wrong. And that makes him dangerous.

Julia Belluz and Steven J. Hoffman looked into some of the “miracle” or “magic” cures Oz has recommended and found that they don’t stand up to scrutiny. Their research uncovered multiple cases in which he recommended a “breakthrough” diet medicine based on no real evidence, and when other physicians and scientists studied those claims, they fell apart. In particular, one of his latest “holy grail” fat busters, “garcinia cambogia,” turns out to be no more effective for weight loss than a placebo. And yet stores like GNC have had to order even more of the stuff because of the demand created by Oz.

Today on KTRS, I talked with Belluz about their investigation and why Oz’s title and appearance (in scrubs or a lab coat) lend a presumed authority to his recommendations, which millions of people accept as fact — despite contrasting opinions from their own physicians, who know their medical situation better than a guy on television. I asked her if Oz benefits financially from these products (a clear conflict of interest), why the broader media hasn’t outed him for fraud, and for details of his unscientific on-air test of green coffee-bean supplements as a fat-burner.

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Read Belluz and Hoffman’s investigative piece for Slate here.