A global review suggests companies make big promises about herbal weight loss supplements, but little weight is actually lost.
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University of Sydney doctoral student Erica Bessell is the lead author of two papers that were presented to the European Congress on Obesity last week, offering the first global analysis of herbal and dietary weight loss supplements.
The study looked at more than 60 supplements that have been investigated in 121 different trials.
The meta-analysis carried found only one herbal supplement - white kidney bean - resulted in statistically significant weight loss.
"However the amount of weight loss was not meaningful from a clinical perspective," Bessell said.
It is believed white kidney beans help reduce the amount of starch absorbed during digestion, resulting in less calories being absorbed.
Bessell suggested people should question the "clever marketing" from supplement companies.
"Companies will use phrases such as 'supports' or 'aid' or 'may assist with'.
"This sort of vague wording is how the companies can get around the regulations that prevent them from making direct claims about the benefit of their product - so watch out for that vague wording."
Sometimes studies were not conducted according to scientific 'gold standards', she said.
"There will always be a risk of bias in studies run by the supplement companies, due to the conflict of interest there. So we need researchers to thoroughly report on their trial design in their scientific papers, so we as the readers can properly assess that risk of bias.
"This is something we actually found was often inadequate in the papers we reviewed.
"The results may even be interpreted in such a way that favours the supplement. Sometimes the evidence isn't even from human studies."
Some supplements are designed to make people feel full so they eat less, some reduce absorption of fats or carbohydrates in the gut, and others aim to alter energy metabolism or fat synthesis.
But Bessell said our bodies were complex machines and many of the products did not produce the promised results.
The researchers found no weight loss was produced by herbal supplements containing green tea or garcinia cambogia, although a combination of green tea, white kidney bean and ephedra showed a slight effect.
African mango, veldt grape and East Indian globe thistle combined with purple mangosteen hold promise, but more research is needed.
Among the dietary supplements that isolated ingredients from their natural source, they found the fibres chitosan and glucomannan, and a fat called conjugated linoleic acid resulted in weight loss, but not a clinically meaningful amount.
Promising results were seen in beta-glucan, fructans, modified cellulose, manno-oligosaccharides, and blood orange juice extract, but few studies have been carried out on these compounds so far.
Bessell said more research was needed on supplement safety, especially when they were taken for long periods or in high doses.
"Most of the reported side effects that we saw were gastro-intestinal side effects, such as bloating or nausea or constipation.
"Most supplements we can buy in store are safe for short term use, though there's often limited or no research on their long term safety.
"There's also a risk of interactions between some supplements and pharmaceutical medications, so people should let their GP or pharmacist know what supplements they're taking."
Supplements sold online were harder to regulate, she said.
One example is epehdra, a herbal supplement banned in many countries, because it has been linked to serious side effects and deaths.
This herbal supplement was still available online, Bessell said.
More research was needed into herbs and compounds that had shown promising results in just a handful of trials, she said.
"I'm sure we'll keep looking to try and find that magic pill.
"In the meantime the best thing to recommend is good old-fashioned healthy eating and exercise," Bessell said.
