An Australian obesity researcher has reviewed 11 of the most common diet pills on the market and found a lack of evidence for their weight loss claims.

The University of Sydney’s Dr Nick Fuller examined for The Conversation the scientific evidence for the following: guarana, acai berry, aloe vera, caffeine, ginseng, green tea, guar gum, chitosan, cayenne pepper, white bean extract and eucommia leaves.

The review is timely given recent warnings of potential liver and kidney damage from the use of over-the-counter weight loss remedies.

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Green tea had the best evidence and was the only product worth buying, according to Dr Fuller.

“Of the ones that were reviewed, the evidence does suggest that maybe green tea in its natural form is something that’s a simple and easy and hopefully safer method that may aid with weight management,” he told The New Daily.

According to Dr Fuller, the available evidence indicated that green tea should be consumed in its natural form, as drinkable tea, not as an extract or supplement.

This is an important message, as green tea extract was recently implicated in a near-death experience.

‘Green tea extract ruined my liver’

Green tea might be good for you if you drink, but green tea extract may be dangerous. Photo: Getty

In February, it was reported that Western Australian man Matthew Whitby needed an emergency liver transplant after taking a protein powder containing green tea extract and garcinia cambogia supplement.

Mr Whitby’s doctors reportedly suspected that the green tea extract was the likely culprit, although this was not definitively proven.

On Tuesday, Health Minister Sussan Ley pledged to talk with the relevant regulator, the Therapeutic Goods Administration (TGA), to determine whether any herbal supplements currently on the market should be delisted.

Sellers of listed products are required by the TGA to hold evidence supporting their effectiveness. But critics say this evidence is rarely audited. A delisted product is illegal to import, export, manufacture and supply.

More research needed

Dr Fuller said the majority of the 11 products he reviewed did not show “any strong evidence” to support their use. Even the evidence for green tea was less than ideal, he said.

More study of popular weight loss products is needed because consumer demand is “exponentially growing”, especially among women, Dr Fuller said.

“There’s a lot more work that needs to be done in this area, particularly around good quality research.

“So we need to make sure that the products we’re taking are safe and they’re effective because when it comes down to it we want to be spending our money effectively on products and services that are helping us.”

Weak evidence for popular products

Dr Fuller told The New Daily that while many studies reported “statistically significant” weight loss, he deemed most of this evidence to be insufficient as the loss was too small.

“Some of them are achieving a small amount of weight loss and often the group reporting on that will say that yes, it was a statistically significantly greater weight loss than the placebo or control group, but that might mean that the group given the diet pill might have lost 0.5 of a kilo and the placebo may have put on 0.5 of a kilo.”

There’s no evidence that acai berries aid weight loss. Photo: Getty

Here is the evidence Dr Fuller found:

• Green tea: “It was estimated that people having green tea achieved a 1.3kg greater weight loss when compared to those taking placebo.”

• Guarana: “as a stand-alone herbal substance is not proven for weight-loss efficacy.”

• Acai berry: “has not been proven to aid with weight loss.”

• Aloe vera: “the weight loss achieved … was not statistically significant.”

• Caffeine: “little evidence that caffeine by itself aids in clinically meaningful weight loss.”

• Ginseng: “it has shown potential and efficacy for weight loss in animal models, but has not yet been proven to work in humans.”

• Guar gum: “no benefit versus placebo.”

• Chitosan: “well-educated randomised controlled trials questioned this potent efficacy.”

• Cayenne pepper: “its individual (stand-alone ingredient) application in the treatment for weight loss is not proven.”

• White bean extract: “several methodological flaws in the studies conducted with such a product make it difficult to draw any firm conclusions.”

• Eucommia leaves: “its efficacy for weight loss in humans is unproven.”

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