Slimming pills are a waste of money – and could be dangerous, according to new research.
They are marketed as boosting metabolism, burning fat and blunting appetite.
But there is “a lack of strong evidence” they actually work, say scientists.
And the misleading claims “have the potential to harm patients,” they warned.
The findings will alarm millions of women hoping to get ‘beach body ready’ for the summer.
Corresponding author Professor John Batsis, a nutritionist at the University of North Carolina, said: “Our findings are important for clinicians, researchers and industry alike.
“They suggest the need for rigorous evaluation of products for weight loss.
“Only then can we produce data that allows clinicians to provide input and advice with a higher degree of certainty to our patients.”
There are hundreds of weight loss supplements in an industry worth billions of pounds a year.
They range from cabbage and green tea extract to the shellfish sugar chitosan, guar gum and conjugated linoleic acid.
One in three Americans trying to lose weight have used one, say the US team.
The analysis by The Obesity Society (TOS) reviewed hundreds of existing studies. Most showed users failed to shed the pounds.
Prof Batsis suggested manufacturers work with academics to design high quality clinical trials.
Patients often struggle to lose or maintain weight because therapies approved by the Federal Drug Administration (FDA) are ineffective.
It is also difficult to access healthcare professionals who provide treatments for obesity.
The National Institutes of Health’s Office of Dietary Supplements now evaluates information and stimulates and supports research.
TOS decided it was important to examine non-FDA therapies to guide its membership by pooling data on 315 randomised controlled trials.
Only 52 were found to be at low risk of bias and sufficient to support efficacy.
Of these, just 16 demonstrated significant before and after differences compared with dummy pills.
Weight loss ranged widely from 10.5 ounces to nearly 11lbs, said the researchers.
TOS’s Clinical Committee, led by Dr Srividya Kidambi who co-authored the study, recommended doctors consider the findings when advising patients.
Added Dr Kidambi, of the Medical College of Wisconsin, Milwaukee: “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.”
The supplements tend to be prescribed by GPs, in combination with diet and exercise, to people who have a significant amount of weight to lose – typically a BMI (body mass index) of 27 or higher.
But some experts have called for them to be banned. The study is in Obesity, the flagship journal of The Obesity Society.
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