If I were a member of the United States Senate, there are a number of people whose opinions I would not solicit about how to handle various pressing problems. I wouldn’t ask Donald Sterling for tips on improving race relations. Rick Perry wouldn’t be my first call when seeking information about combatting LGBT intolerance. And of course, I’d know better than to ask Jenny McCarthy for the facts about vaccines.

When contemplating how to solve a problem, seeking counsel from people who are making the problem worse doesn’t make a lot of sense. So why is Senator Claire McCaskill inviting Dr. Mehmet Oz to testify about weight-loss diet scams? Is she looking for tips in how to sell them?

According to a statement from Sen. McCaskill’s office, the cardiologist and Oprah Winfrey protégé will testify this coming Tuesday about sham obesity remedies, specifically green coffee. It seems that shortly after the product was featured on his show, a purveyor of this miracle weight-loss treatment started hawking it at $50 for a one-month supply. I suspect Dr. Oz will express shock (shock!) that some bad actor out there would abuse people’s trust, and the Senator will bask in the attention his celebrity brings to CSPAN.

Except, of course, that green coffee is totally worthless as a weight loss supplement in the first place.

Dr. Oz’s involvement with sham obesity treatments isn’t just limited to green coffee. He is also quite happy to shill for garcinia cambogia, which he calls the “newest, fastest fat-buster.” Never mind that no studies have shown a weight-loss benefit after 12 weeks of taking it, and several studies have demonstrated no such benefit at all. The only thing that seems supported by reliable evidence is that it probably won’t hurt you, which I guess is reason enough for Dr. Oz to fall all over himself promoting it.

The unmitigated claptrap that Dr. Oz promotes doesn’t stop at weight-loss treatments, either. He’ll help you choose “the right cleanse for your body type.” (Correct answer: none of them.) He’ll give you tips about creating a homeopathy starter kit, despite homeopathy being a preposterous pile of pseudoscientific malarkey. He’s featured Dr. Joseph Mercola, a man who (among other things) urges parents to skip the vitamin K shot that will prevent a potentially devastating bleeding disorder in their infants.

As a physician, Dr. Oz’s credentials are truly impressive. He is the vice-chairman of surgery at one of the nation’s top medical schools, after all. But somewhere along the way he decided that his fame was more important than his credibility, as demonstrated by his willingness to promote treatments that fail to withstand even the barest scientific scrutiny.

Even so, if Sen. McCaskill were inviting him to offer testimony about innovative surgical treatments, I’d have nothing to say about it. But she’s not. She’s asking him to speak about a problem to which he has repeatedly contributed. Unless Sen. McCaskill is drawing the spotlight in order to ask Dr. Oz why he is selling worthless goods to his viewers, the spotlight itself must be the only point in asking him to show up at all.