UPDATED 3/30 12:30 p.m. ET: Supplement companies are scrambling to release a new weight-loss aid called red raspberry ketone. Just today, Pure Health released a 400 mg capsule. Their timing couldn't have been better: Dr. Mehmet Oz touted the aromatic compound, derived from red raspberries, on his show, calling it "the number one miracle in a bottle."
As Oz explains, raspberry ketone, or RK, may stimulate the production of adiponectin, a hormone found in fatty tissue that improves our ability to metabolize fat. RK is similar in structure to capsaicin, according to researchers -- an extract from hot peppers that is similarly associated with improved fat metabolism. Studies show that thin people have higher levels of adiponectin than overweight and obese people. What's more, researchers agree that the hormone helps regulate weight.
"Adiponectin actually improves insulin sensitivity and will result in weight loss," says Mark Hyman M.D., author of The Blood Sugar Solution. Still, he thought the claims about the supplement were a stretch.
After all, the studies that investigate RK's effect on adiponectin and weight loss were conducted in mice, not people. To date, there have not been any human trials to back up these claims. Without a single long-term study of the compound's effects on humans, any health claim is pure extrapolation. Still, the studies in mice do show some promise. Most recently, a 2010 study from Korea's Food & Drug Administration found that male mice who were given a high-fat diet along with an RK supplement had elevated secretion of adiponectin and, along with that, increased metabolism of fatty acids and less fat storage.
A similarly-designed 2005 study from Japan found that mice given a high-fat diet for six weeks and then, for an additional five weeks, the same high-fat diet along with one percent RK. They found that the supplement prevented weight gain, fat accumulation around the liver and triglyceride levels associated with eating the high-fat food. But many experts remain skeptical that such results can be replicated in people.
"RK might make 3T3L1 cells engage in lipolysis, but that is a far cry from doing it in humans," Dr. Robert Lustig, a neuroendocrinologist and professor of pediatrics in the Division of Endocrinology at University of California, San Francisco wrote about the research in an email to Healthy Living. What's more, "adiponectin correlates inversely with fat cell mass, but no one has shown the giving adiponectin reduces fat cell size."
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