The Obesity Society publishes the definitive supplement review: 16 of 315 trials

Researchers writing in Obesity, the flagship journal of The Obesity Society (TOS), reviewed 315 randomized controlled trials of dietary supplements and alternative therapies for weight loss and found little strong evidence that they work. The paper, "A Systematic Review of Dietary Supplements and Alternative Therapies for Weight Loss," appears in the July 2021 print issue, with an accompanying perspective from the society's Clinical Committee ^[2].

The findings matter because supplements are a huge part of how Americans try to lose weight. There are hundreds of weight-loss products on the market — green tea extract, chitosan, guar gum and conjugated linoleic acid among them — and an estimated 34% of Americans trying to lose weight have used one ^[2].

What the review found

The team searched Medline (PubMed), the Cochrane Library, Web of Science, CINAHL and Embase (Ovid), following PRISMA systematic review guidelines, and limited the analysis to trials in adults 18 and older ^[2].

Of the 315 peer-reviewed randomized controlled trials analyzed, only 52 were classified as low risk of bias and sufficient to support efficacy. Of those 52, just 16 showed a significant difference in weight between the supplement group and placebo. In those 16 studies, the extra weight loss ranged widely, from 0.3 to 4.93 kilograms — roughly 0.7 to about 10.9 pounds ^[2].

Put another way: most of the studies showed the supplements did not produce weight loss among users ^[2].

"Our findings are important for clinicians, researchers, and industry alike as they suggest the need for rigorous evaluation of products for weight loss," said corresponding author John Batsis, MD, of the University of North Carolina School of Medicine and the UNC Gillings School of Global Public Health. "Only then can we produce data that allows clinicians to provide input and advice with a higher degree of certainty to our patients" ^[2]. Batsis added that the supplement industry and academic researchers should work together to design high-quality trials ^[2].

The authors also noted why patients turn to these products in the first place: some struggle to lose weight or keep it off because FDA-approved therapies do not work well enough for them, and others lack access to health professionals who treat obesity ^[2].

The society's call to clinicians and regulators

The companion perspective, "Dietary Supplements and Alternative Therapies for Obesity: A Perspective from The Obesity Society's Clinical Committee," was led by Srividya Kidambi, MD, MS, of the Medical College of Wisconsin, who also co-authored the review ^[2]. It recommends that clinicians consider the lack of evidence behind non-FDA-approved supplements and therapies and guide patients toward tested weight-management approaches ^[2].

The committee went further on policy: "Public and private entities should provide adequate resources for obesity management. 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" ^[2].

Why it matters for patients

The practical takeaway is about the quality of evidence, not just the size of the effect. Even among the small group of trials judged low risk of bias, only 16 beat placebo, and the largest reported difference was under 5 kilograms ^[2]. That is the ceiling of what the best-designed supplement studies showed — and the authors describe those studies as "methodologically distinct," meaning they were not directly comparable to one another ^[2].

For anyone weighing a supplement against a prescription obesity treatment, this review is a reminder that products sold over the counter are not held to the same evidence standard as FDA-approved drugs. The review looked specifically at dietary supplements and alternative therapies; it was not a head-to-head comparison with prescription medications, and the sources here do not report results for any GLP-1 drug ^[2].

Cost is the other piece. Americans spend billions on these products ^[2], and the review does not report how much the 16 "successful" supplements cost or how long their effects lasted.

What is not yet known

The sources do not say which specific supplements were among the 16 that beat placebo, how long those trials ran, or what side effects were reported. They also do not describe how many total citations were screened before the 315 trials were selected. Those details are in the full paper, which is not reproduced in the material available here.

Several authors disclosed industry relationships, including consulting or speaking arrangements with Novo Nordisk and AstraZeneca, and Batsis's work was supported in part by the National Institute on Aging (K23AG051681). The Obesity Society provided no funding for the manuscript ^[2].