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When Dr. Mehmet Oz speaks, his fans listen. But even the people who work on his television show were taken aback by the overwhelmingly positive reaction that his endorsement of a little-known supplement called raspberry ketone received.

"For some reason, raspberry ketones had an outsized response," said Tim Sullivan, spokesman for The Dr. Oz Show.

Since he mentioned the weight-loss supplement on his show last February and again in April, countless companies seem to have popped up to sell the products and health food stores have been inundated with requests.

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What is this so-called "miracle" substance? And more importantly, does it work?

The breakdown

Raspberry ketone is the substance in raspberries that give them their distinctive smell. It's commonly used as a flavour enhancer and is also approved for use in natural health products in Canada. Although it's touted as a natural compound, much of the raspberry ketone products on the market are made synthetically. Raspberry ketone occurs naturally in only very small amounts, so companies produce it in a lab.

On his show, Dr. Oz touted the compound – even using the phrase "miracle in a bottle to burn your fat." He explained it acts on adiponectin, a hormone that regulates metabolism, "tricking" the body into burning fat at a faster level.

Although Dr. Oz cautioned that raspberry ketone is an aid that should be paired with a healthy lifestyle, the message was loud and clear: This compound leads to weight loss.

The reality

The weight-busting capabilities of raspberry ketone have been scrutinized in only a few studies. The research has been based on mice or conducted in test tubes. For instance, one study found that mice fed a high-fat diet while consuming raspberry ketones were able to reduce their fat levels.

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Sounds convincing, but no comprehensive studies have been completed in humans. Weight-loss experts offer the old adage, "If it sounds too good to be true, it probably is."

Yoni Freedhoff, medical director of the Bariatric Medical Institute in Ottawa and an expert on obesity and nutrition issues, highlighted several shortcomings in the mouse study. First, the animals were fed high doses of raspberry ketone – about 2 per cent of their body weight. That would translate to far more than a human would be likely to consume on a daily basis for a prolonged period.

"I don't think we're ever going to escape the fact if you consume more calories than you burn, you're going to struggle with your weight, and there's no product that's going to protect you from that," Dr. Freedhoff said.

Arya Sharma, scientific director of the Canadian Obesity Network, said that raspberry ketone appears to act on the body by driving stress hormones, which is "the last thing you want," as that can lead to problems such as increased heart rate.

Dr. Sharma also pointed out that even if consumed in a natural form, raspberry ketone could have unknown side effects or interactions with other medications. But people often feel desperate to lose weight and are willing to try anything. Dr. Sharma said better regulations and tighter rules should be put in place to restrict the types of weight-loss claims companies are allowed to make.

"The science is just not there. The studies aren't there," Dr. Sharma said. "I would not be spending my money on any of this stuff."

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At The Dr. Oz Show, Mr. Sullivan noted that companies take it upon themselves to aggressively market products, sometimes in irresponsible ways, which is difficult for the show to control.

The bottom line

While the promise of the synthetic compound sounds alluring, the best way of losing weight hasn't changed: It's still diet and exercise.

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