Evidence on Weight-Loss Supplements Found Too LightWednesday, March 30, 2011
Although this is a billion dollar market, most users of these products (after spending a fortune) will have realised that virtually none of them hold any of the advertised promises (viz. boosts your metabolism, burns fat, reduces appetite, abolishes hunger, shaves inches off your waistline, etc.).
Apparently, this is not just YOU for whom these products do not work – it turns out that the published scientific evidence (by no means available for all such products) is rather light (pun intended!).
Thus, a recent review of reviews on the evidence in support of such weight-loss supplements, published by Igho Onakpoya and colleagues from the University of Exeter, UK, in a recent issue of OBESITY, concludes that:
“…the existing systematic reviews of clinical trials testing the efficacy of food supplements in reducing body weight fail to provide good evidence that any of these preparations generate clinically relevant weight loss without undue risks.”
For their paper, the researchers conducted an extensive search of all relevant databases to identify review articles summarizing the data on individual weight-loss supplements.
Published reviews that met the eligibility and quality criteria were available only for the following supplements with rather modest (not to say non-existent) findings:
Guar gum: 20 randomized controlled trials (RCTs) including 366 participants: not efficacious for reducing body weight.
Chromium picolinate: 17 RCTs with 961 participants: a “relatively small” effect in reducing weight.
Ephedra: 17 RCTs with 1,451 participants: a significant short-term effect on body weight. Serious risks of Ephedra/ephedrine intake were also identified.
Citrus aurantium (bitter orange): 1 clinical trial with 23 participants: no significant effect on body weight.
Conjugated linoleic acid: 21 clinical trials with 852 participants: no significant effect on body weight.
Calcium: 13 RCTs with a total of 1,127 participants: no significant effect on body weight.
Glucomannan: 14 RCTs with 531 participants: significant (albeit small) reduction in body weight.
Chitosan: 15 RCTs with 1,219 participants: some evidence of short-term weight loss in obese and overweight individuals.
Camellia sinensis (green tea): 15 trials with 1,226 participants: efficacious for short-term weight reduction and weight maintenance.
Overall the authors come to the rather sobering conclusions that:
“Generally speaking, the results and conclusions of the systematic reviews are disappointing. In particular, they are limited by the often small sample sizes and low quality of the primary studies, and by the fact that some of them fail to control for lifestyle variables with important influence on body weight.”
The authors also don’t appear happy with the quality of the reviews:
“…several of the systematic reviews are flawed, for instance, through insufficient search strategies or a failure to account for the methodological quality of the primary studies. Systematic reviews that reported a “statistically significant effect” are limited by small effect sizes (e.g., chromium picolinate), and/or a high risk of adverse events (e.g., Ephedra). Clinically significant weight loss of at least 5% of body weight was not achieved. The short duration of most of the primary studies is a further drawback. Therefore, none of the nine food supplements discussed above are supported by sound evidence from systematic reviews for generating clinically relevant effects on body weight without undue risks.”
Not that any of this is likely to cut into the profits of the “all-natural” weight-loss supplement market – after all it is hard to get people to stop spending their hard-earned dollars on hope (and of course, it is their money to spend).
Nevertheless, this is the kind of information that is likely to be available to Canadians through the COACH initiative.
I know I could be opening a can of worms by asking my readers to share their insights and experience with weight-loss supplements but I am guessing that other readers will probably find this of interest.
Onakpoya IJ, Wider B, Pittler MH, & Ernst E (2011). Food supplements for body weight reduction: a systematic review of systematic reviews. Obesity (Silver Spring, Md.), 19 (2), 239-44 PMID: 20814412