With ingredients ranging from cabbage to bitter orange and guar gum, hundreds of herbal food supplements are sold as diet aids and snapped up by consumers desperate to slim.
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But experts say people are wasting millions of pounds a year on slimming pills that may, at best, have only a placebo effect.
Researchers from the Peninsula Medical School at the universities of Exeter and Plymouth said there was no evidence that many of the drugs work, while research from the University of Gottingen in Germany found people on supplements based on cabbage powder, bean concentrate and plant extracts did not lose any more weight than those taking a fake pill.
The researchers told the International Conference on Obesity in Stockholm: “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.”
A Google search pinpoints several websites promising products to help drop a dress size in eight days or lose 12 pounds in 12 days for as little as £11 for a month’s supply.
They are also increasingly sold in high-street health food shops and pharmacies, with claims ingredients such as calcium and green tea will help to boost weight loss.
But Professor Naveed Sattar, professor of metabolic medicine at Glasgow University, said there was little evidence that diet supplements were effective.
He said: “It might give you a placebo effect but if you fall back into the same old habits you will go back to the weight trajectory you were on. I don’t think the evidence base is that strong.
“The reality is that in terms of weight loss people need to make sustainable changes in lifestyle, particularly dietary habits. It is not an easy thing to do. There are a lot of people in Scotland who were weaned on Irn Bru and high-fat foods. Their taste buds are used to those things. For them to make sustainable changes is a really tough ask. What people don’t realise is it takes time to retrain your taste buds. There are no quick fixes.”
Only one drug -- Orlistat -- is licensed for use in the treatment of obesity. It is available at pharmacies, under the name Alli, to patients with a BMI of 28 or more.
However, other products also claim to be backed by scientific research. A trial at the University of Oklahoma found that Capsiplex, which is made from capsicum extract and is reportedly used by Jennifer Lopez and Britney Spears, can help burn as many calories as a 25-minute jog.
Other herbal supplements that have won celebrity endorsements include TrimSecrets, launched by Michelle Mone and herbalist Jan de Vries after the businesswoman lost more than six stones in 18 months with the help of the pills.
About 50,000 tins of the pills, which contain guarana caffeine, green tea extract and citrus fruits powder, were said to have been sold in the first two weeks after their launch, but the supplements were criticised by Professor Mike Lean, professor of human nutrition at Glasgow University, who described them as “no better than chalk pills”.
In a paper published by the Scottish Public Health Observatory in 2007, Lean said high-street stores such as Boots and Holland & Barrett were stocking “quack” supplements that made “outrageous and unsubstantiated” claims to aid weight loss even although there was no or little medical evidence behind them.
Nutritionist Dr Carrie Ruxton, a member of the Scottish Food Advisory Committee, said some supplements may help motivate consumers to improve their diet and exercise regime. But she warned: “Supplements for weight management are no substitute for a calorie-controlled diet and exercise as a means of controlling weight.”
Robert Verkerk, executive and scientific director of the Alliance for Natural Health, said some herbal and natural products could offer help for slimmers. He said: “There is plenty of evidence that some products are very helpful, but by and large they cannot be taken in isolation and they should be coupled with an altered diet and lifestyle regime which incorporates an abundance of exercise.
“One great concern is there is a big difference between the type of product a herbal practitioner will offer, or even those on offer in health shops, and some of the products on the internet. It is a completely unregulated part of the market.”
The products that can put health at risk
The US Food and Drug Administration has recalled 60 slimming products found to contain undeclared, active pharmaceutical ingredients amid warnings they could put consumers’ health at risk. The Medicines and Healthcare Products Regulatory Agency has advised consumers to stop taking any of the products but several are still available online, including Royal Slimming Formula and Miaozi Slimming Capsules.
Gi Capsules, which claimed to contain a special fruit vinegar that slowed down the release of carbohydrates and sugars from food, were withdrawn from sale in the UK after concern over weight-loss claims. The makers, Global DM Licensing, claimed that dieters taking one capsule a day could burn off 10 pounds in the first week and then six pounds every week after that. The firm withdrew the product after the Office of Fair Trading requested evidence to support the claims.
In September a TV advert for LIPObind, marketed as the UK’s best-selling slimming pill, was banned by the Advertising Standards Authority. The product contains dried cactus extract. The ASA said there was inadequate evidence to substantiate weight-loss claims. The decision followed another adjudication that forced makers Goldshield to remove the slogan “The NEW Clinically Proven Fat Binding Pill ... A pill that has been tried and tested and proven to bind fat” from a press advert.