Rasberry ketone capsules sell fast, but human trials on effects are lacking. (Ricardo DeAratanha / Los…)
Until recently, very few people had ever heard of raspberry ketones, the aromatic compounds that give the berries their distinctive smell. Today, health food stores have trouble keeping the capsules or drops of the stuff on their shelves. Almost overnight, an obscure plant compound became the next big thing in weight loss — and all it took was a few words from Dr. Oz.
In a February episode of "The Dr. Oz Show," Mehmet Oz told viewers that raspberry ketones were "the No. 1 miracle in a bottle to burn your fat." Once Oz calls something a "miracle," it doesn't remain obscure for long.
"An adjective like 'miracle' is used as an editorial device to describe anecdotal results, as exemplified by the guests on our show. Our audience are not scientists, and the show needs to be more lively than a dry scientific discussion," a spokesman for the show, Tim Sullivan, said in a statement, adding that the show does not view supplements as "magic bullets."
"Absolutely, my patients are asking about it," says Dr. Peter Lipson, an internist and clinical assistant professor of medicine at Wayne State University School of Medicine in Detroit. "I tell them that I don't know if it will help, and neither does anyone else."
Even the staff at the show found the response to be "unexpectedly zealous," Sullivan says.
A handful of studies from Asia suggests that raspberry ketones — which are chemically similar to capsaicin, the heat compound from chile peppers — might help burn fat, especially the fat that builds up in the liver. The reported benefits are impressive: lower cholesterol, increased sensitivity to insulin and, yes, weight loss.
But these studies all had a serious shortcoming: They involved rodents or cells in test tubes, not people. And that's a deal-breaker, says Melinda Manore, professor of nutrition at Oregon State University in Corvallis. She notes that a lot of weight-loss supplements that look promising in laboratory rodents fail to pan out in the real world. "I would not recommend this product until there is some evidence that it works," she says.
Some of the hype around raspberry ketones might actually be justified, says Stephen Anton, an assistant professor of aging and geriatric research at the University of Florida in Gainesville. "I don't know if I'd use the word 'miracle,'" he adds.
Anton, a paid consultant for Re-Body, a supplement company that is developing a raspberry ketone product of its own, has studied the weight-loss potential of several plant compounds. "This is something that looks promising, but you need clinical trials to validate the promise," he says.
A 2012 study from China found that raspberry ketones had several health benefits — including improved insulin sensitivity and reduced fat in the liver — in rats fed a high-fat diet. Anton compares such results to early studies of resveratrol, a plant compound that first showed heart-healthy benefits in animals before it became a popular ingredient in supplements. Later studies suggest that it helps human hearts too.
The Dr. Oz television segment featured before-and-after pictures of women who said they lost significant weight while taking raspberry ketone supplements. But Oz noted that the women had also dieted and worked out. The Dr. Oz website says that raspberry ketones work best "when paired with regular exercise and awell-balanced diet."
Nothing discussed on Oz's show "should be considered as a substitute for the basic tenets of diet and exercise," Sullivan says. "Anything strong enough to help you is strong enough to hurt you" is something Oz says frequently, according to Sullivan.
Diet and exercise — the real secret to weight loss — are not much of a secret at all, Lipson says. He adds that the old-fashioned approach doesn't make for great television, which is why he thinks Oz and other television personalities end up touting new, exciting products that may or may not work.