Little to no evidence weight-loss supplements work, large review finds

Over one third of Americans attempting to lose weight have at some point tried an over-the-counter weight-loss supplement. A new systematic review of over 300 clinical trials has found little to no evidence any of these supplements actually work, and the researchers are calling on regulatory authorities to take action.

Dietary supplements are not considered “drugs” by the US Food & Drug Administration (FDA), so as long as they are “generally regarded as safe” they can be sold without any clear evidence of effectiveness.

A new systematic review has analyzed 315 randomized controlled trials, investigating the quality of evidence presented for the efficacy of 14 dietary supplements or alternative therapies for weight loss. Included in the analysis were trials testing acupuncture, chitosan, cocoa, chromium, green tea, guar gum and linoleic acid.

Only 52 studies analyzed (16.5 percent) were noted as of low risk for bias, and of those, just 16 were found to present clinically significant differences in weight loss between active and placebo groups. No specific supplement stood out as particularly efficacious but senior author Srividya Kidambi says the big takeaway is just how poor most of these studies actually are.

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

The big problem raised here by the researchers is not a new one. Previous studies have taken aim at unregulated weight loss supplements, finding the claims of effectiveness are rarely backed up by good clinical evidence.

This is largely due to a loophole in US regulations allowing supplements to make specious claims as long as they are not suggesting they actually cure a disease. So you can’t say this herbal supplement cures cancer but you can say it enhances weight loss. And, if you have done some kind of clinical trial then you can even say there is clinical evidence to back up your claims, even if that evidence is mostly of low quality.

Kidambi and colleagues penned an additional perspective article to accompany the new research. In the article they call on doctors to keep in mind the weak evidence for these supplements, and urge them to recommend proven weight-loss methods to their patients. The researchers also press organizations such as the FDA to better regulate the entire multi-billion-dollar supplement industry.

“We call on regulatory authorities to critically examine the dietary supplement industry, including their role in promoting misleading claims and marketing products that have the potential to harm patients,” the researchers write.

The new study was published in the journal Obesity.

Source: University of North Carolina Gillings School of Global Public Health