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The terrible science behind popular weight loss products

“The entire systematic review is comprised of very poorly conducted studies.”

vitamins, supplements
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Back in 2012, daytime TV celebrity Dr. Oz touted the benefits of a miraculous new weight loss solution: green coffee bean extract.

He cited a study he claimed proved it. People, he said, didn’t need to change what they ate or how they exercised. They could simply “do whatever they wanted to do” and in the process lose “a pound per week.”

Spoiler alert: the study was bad and the data flawed. Green coffee bean extract amounted to an expensive placebo and six years later, Dr. Oz lost a $5.25 million lawsuit over the false advertising.

But before you dismiss this as an isolated byproduct of medical quackery, consider this: Americans still spent $61 billion on weight-loss products last year, and more than $2 billion on weight loss pills alone, according to an estimate by Marketdata LLC. (That’s almost three times the total value of all the carrots in the U.S. in 2020.)

Hundreds of flawed “clinical” trials like the one Dr. Oz referred to lend things like raspberry ketones, yacon syrup, and saffron extract a veneer of credibility.

Poor data linked to this industry “continues to accumulate,” Srividya Kidambi tells Inverse. Kidambi is an associate professor and chief of endocrinology and molecular medicine at the Medical College of Wisconsin and the senior author of a review of dietary supplements and “alternative therapies” published Wednesday in the journal Obesity. Her work suggests many studies on these products are biased and of the few that aren’t, most can’t prove they actually contribute to weight loss.

“It's interesting how much people are sold on anecdotal evidence and use that in lieu of the randomized, controlled trials that we have come to expect from all the other drugs,” Kidambi says.

How the discovery was made — Researchers cast a wide net to find almost 2,000 full-text articles on dietary supplements, and then further narrowed them down to exclude everything but randomized, controlled trials on humans — the bare minimum for reliable evidence that a treatment works.

Randomized and controlled means that a test group (using the supplement) was compared with a similar control group (not using the supplement) and that the treatment status was assigned randomly. This left 315 articles that measured fat loss, weight loss, or BMI, specifically.

The researchers determined which treatments had five or more of these higher-quality randomized trials, and evaluated the research on these treatments or supplements:

  • Acupuncture
  • Calcium & vitamin D
  • Chitosan
  • Chocolate/cocoa
  • Chromium
  • Ephedra or caffeine
  • Garcinia and/or hydroxycitrate
  • Green tea
  • Guar gum
  • Conjugated linoleic acid
  • Mind-body (tactics like mindfulness, stress management, hypnosis, meditation, and massage)
  • Phaseolus
  • Phenylpropylamine
  • Pyruvate

What’s new — Kidambi and colleagues reviewed these articles for bias using a standardized scale. Some of the most common problems with the biased studies were:

  • Small sample sizes
  • Testing on a study population that didn’t resemble the people who would be buying the product
  • Not specifying whether or not a purported change in weight was statistically significant

In some cases, “whatever number looks good seems to be reported,” says Kidambi.

Separately, they also looked at which studies found statistically significant weight loss effects. They then determined how many studies for each treatment had both a “low risk of bias” and a significant weight loss effect.

Dr. Oz at the 2019 Time 100 Health Summit. At a U.S. Senate committee hearing in 2014, he was criticized for perpetuating weight-loss scams.

Brian Ach/Getty Images

Very, very few of the 315 studies met this threshold. Based on their criteria, only 52 studies were “high quality” and of those, only 16 showed a significant weight loss difference between groups that had used the treatment and those that hadn’t.

Those 16 weren’t concentrated in one treatment or pill, per se, but spread out among them. Phaseolus, a white kidney bean extract, for example, had no unbiased studies backing it.

Perhaps more surprising, says Kidambi, were how many popular weight loss supplements the researchers came across with almost no studies at all — biased or unbiased — to back them up. Treatments like Nav Plus infusions and raspberry ketones didn’t even make it into the review because of how little the researchers could find.

“The entire systematic review is comprised of very poorly conducted studies,” Kidambi says. “But even among them, there are these very popular supplements that have really no evidence at all.”

A flow chart shows which “studies” on dietary supplements for weight loss were eliminated from the review and why.

Obesity / Batsis, et al.

Why these results matter — To scientists and some consumers, it’s likely no surprise most weight loss supplements and treatments aren’t backed by robust evidence. The supplement industry is loosely regulated, reducing incentives for companies to produce convincing evidence that their weight-loss claims are true.

Still, the weight loss industry remains a behemoth: A money-making enterprise that uses tactics like celebrity endorsements and doctored images to convince people there’s a quick and easy way to shed pounds. This study further reinforces the fact that the majority of weight loss products are not medicines backed by empirical evidence.

A popular, but disputed, weight loss product is “raspberry ketones.”

Getty Images

These findings don't necessarily mean all weight loss supplements can’t work — but it’s extremely difficult to determine which ones do. Furthermore, some weight loss supplements have even been linked to a number of deaths.

Because so few of the “quality” studies found an effect, it’s likely safer to skip a weight-loss supplement, which could contain unlisted ingredients, in favor of science-backed strategies like diet and exercise.

What’s next — The authors note in the review that high-quality studies on weight loss treatments and supplements are badly needed. We also need stricter regulations covering how weight loss products are marketed, Kidambi says.

“It needs to be that when something is implying clinical benefit if it is in the obesity management aisle, I think there has to be some stricter supervision of that product,” she says.

Under the supervision of the FDA and FTC, weight loss supplements are technically allowed to advertise how effective they are, as long as they don’t claim to cure a disease. Because of this, companies often use studies, including bad ones, to put claims like “clinically proven to help with weight loss” on a supplement label.

As Kidambi and colleagues write in a perspective paper published alongside their review:

“Misleading claims can be prosecuted by the Federal Trade Commission (FTC), but this is a process of limited impact, given that thousands of products are continually brought to market, overwhelming FTC’s capacity.”

Few consumers seeking to lose weight are likely to dig into scientific papers before trying out a weight loss product anyway, so even if more companies did have independent researchers conduct high-quality, unbiased trials, it may not stop other weight loss supplement companies from conducting bad research or worse — selling products completely unsupported by evidence. This is why regulations need to be improved overall.

Evidence-backed FDA-approved drugs (not supplements) that help with weight management are available, Kidambi says. These include Alli, phentermine, and naltrexone-bupropion, among others. The problem, she explains, is that many insurers don’t cover them — or, for that matter, other preventive services like visits to a dietician.

“It's funny that once patients get diabetes, everything is covered,” she says. “But when patients [have] a weight issue that will put them at risk for diabetes, very few resources are available.”

For now, Kidambi says, it’s best to consult with a medical provider if considering a weight loss product. “I think if there is some legitimate use of these, your provider will know,” she says.

Objective: Dietary supplements and alternative therapies are commercialized as a panacea for obesity/weight gain as a result of the minimal regulatory requirements in demonstrating efficacy. These products may indirectly undermine the value of guideline-driven obesity treatments. Included in this study is a systematic review of the literature of purported dietary supplements and alternative therapies for weight loss.
Methods: A systematic review was conducted to evaluate the efficacy of dietary supplements and alternative therapies for weight loss in participants aged ≥18 years. Searches of Medline (PubMed), Cochrane Library, Web of Science, CINAHL, and Embase (Ovid) were conducted. Risk of bias and results were summarized qualitatively.
Results: Of the 20,504 citations retrieved in the database search, 1,743 full-text articles were reviewed, 315 of which were randomized controlled trials evaluating the efficacy of 14 purported dietary supplements, therapies, or a combination thereof. Risk of bias and sufficiency of data varied widely. Few studies (n = 52 [16.5%]) were classified as low risk and sufficient to support efficacy. Of these, only 16 (31%) noted significant pre/post intergroup differences in weight (range: 0.3-4.93 kg).
Conclusions: Dietary supplements and alternative therapies for weight loss have a limited high-quality evidence base of efficacy. Practitioners and patients should be aware of the scientific evidence of claims before recommending use.
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