Neither of the studies, presented at the International Congress on Obesity in Stockholm, Sweden, have yet to be published.

According to the author of one of the papers, the science backing a variety of weight loss supplements is lacking.

“The market for these is huge, but unlike for regulated drugs, effectiveness does not have to be proven for these to be sold,”​ said Dr Thomas Ellrott, head of the Institute for Nutrition and Psychology at the University of Göttingen Medical School, Germany.

“Few of these supplements have been submitted to clinical trials and the landscape of products is always changing, so we need to put them through rigorous scientific evaluation to determine whether they have any benefit,” ​he said.

Manufacturers of weight management dietary supplement products contacted by NutraIngredients.com stressed the robustness of the science backing the efficacy of their products.

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Placebo-controlled trial​

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Dr Ellrott’s study was a randomized, placebo controlled, partly blinded eight-week trial, where 189 overweight or obese individuals were given either a weight loss supplement in doses recommended by the manufacturers, or a placebo.

The nine supplement products tested were purchased at pharmacies in Germany. Labelled active ingredients were: Polyglucosamide, cabbage powder, Konjak extract, sodiumalginate-complex, bean concentrate, selected plant extracts, L-Carnitine,

fibre formulation and Guarana seed powder.

Significant weight loss was found for seven of the supplements (between 1kg and 2kg), but none of these resulted in “a significantly greater weight loss than placebo ​(1.2kg).” ​

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Systematic literature review​

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The second study, led by Dr. Igho Onakpoya of Peninsula Medical School at the Universities of Exeter and Plymouth, UK, claims to be “the first systematic review of all existing systematic reviews of clinical trials on weight loss supplements.”​

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Literature searches were conducted in five electronic databases to identify all relevant articles on nine popular slimming supplements. These include: chromium picolinate, Ephedra, bitter orange, conjugated linoleic acid (CLA), calcium, guar gum,

glucomannan, chitosan and green tea.

The reviews, conducted by two independent reviewers, did not find any evidence that any of the supplements was “an adequate treatment for reducing body weight”.​

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According to Dr Onakpoya, the quality of the trials on the dietary supplement ingredients was “very poor”,​ due to poor randomization techniques, allocation concealment, blinding issues and short duration.

“The conclusions from the authors of the systematic reviews themselves mostly found that the weight loss was not clinically significant, meaning at least 5 per cent loss of initial body weight,”​ he told NutraIngredients.com. The only clinically significant results were found for ephedra, he said.

Drugs are better​

Dr Ellrott’s study, which did not receive any funding, concluded that the weight loss drug orlistat should be used instead of dietary supplements due to its “proven efficacy and safety”.​

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Dr Onakpoya’s position is funded by an unrestricted grant from the drug firm GlaxoSmithKline (GSK), which manufactures orlistat under the brand name alli – ​which only recently became available over-the counter in the US and Europe.

In 2008, when alli ​became the first weight loss drug in the US to be sold without a prescription, GSK had petitioned the US Food and Drug Administration to reclassify all weight loss claims as disease claims – which would essentially push dietary supplement products (which make weight loss health claims) out of the weight loss market. For more on that, click here​.

Supplements supported​

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According to one supplement ingredient manufacturer contacted for comment, the Dr Onakpoya’s literature review “was not thorough enough”.​

Cognis, which manufactures CLA, one of the ingredients reviewed by Dr Onakpoya’s team, stressed that its branded CLA – Tonalin – has been proven to influence fat reduction.

“Tonalin has 18 studies published in peer reviewed journals supporting its role in weight management and we continue to see positive research that supports how CLA safely reduces body fat, maximizes lean muscle and prevents fat cells from refilling,”​ said the firm.