Food supplements designed to speed up weight loss do not work, experts say.
A range of supplements -- including those based on cabbage, fibre and plant extracts -- are no better than "fake" dummy pills in helping people slim, they warned.
Presenting their findings, experts from the Peninsula Medical School at the universities of Exeter and Plymouth said there is no evidence the drugs actually work.
In a separate study, German researchers found no evidence supplements aid weight loss.
The UK team reviewed existing data, including on guar gum, bitter orange, calcium, glucomannan (a dietary fibre), chitosan (listed as a fat absorber), chromium picolinate (sometimes sold as an appetite suppressant) and green tea.
Presenting their findings at the International Conference on Obesity in Stockholm, they wrote: "The findings from systematic reviews fail to provide sufficient evidence that any food supplement can be recommended for reducing body weight.
"A wide range of herbal and non-herbal food supplements is currently being promoted for weight loss.
"While mainstream drugs for body weight reduction must demonstrate efficacy before receiving a licence, food supplements do not need to meet this requirement.
"Few food supplements have therefore been submitted to clinical trials, and many healthcare professionals feel uncertain about their therapeutic value."
Meanwhile, experts at the University of Gottingen in Germany carried out an eight-week trial on nine common weight loss supplements bought over the counter. These included cabbage powder, bean concentrate, some plant extracts and a fibre formulation.
A total of 189 overweight people were split into 10 groups, with some given the weight-loss supplements.
While those on the supplements did lose weight, they did not lose any more than people taking a fake pill.
The authors wrote: "All tested over-the-counter products for weight reduction showed no better efficacy than placebo."
Victoria Taylor, senior heart health dietician at the British Heart Foundation, said: "There are no quick fixes when it comes to weight loss.
"A huge amount of money is spent on the dieting industry, but it's often money down the drain."