The list of over-the-counter dietary and weight loss supplements is exhaustive, with the majority based on scant supporting evidence from studies conducted in humans to support their claims.

Weight-loss products make up one of the largest growing markets in the world. While the Therapeutic Goods Administration is cracking down on the claims associated with complementary medicines, only about one-fifth are evaluated for compliance each year.

Here I’ve evaluated some of the most commonly used products for weight loss for their effectiveness (but not necessarily safety).

Guarana

Guarana is high in caffeine and derived from the seeds of a South American tree. A short-term double-blinded randomised controlled study (the gold standard of trials where a treatment is tested relative to a placebo) was conducted over eight weeks.

It showed a herbal combination of guarana and Ma Huang (a medicinal preparation from the plant Ephedra sinica) to be effective for weight loss (-4.0kg versus -0.8kg for placebo) and fat loss.

However, despite its proven efficacy for short-term weight loss, its safety is questioned. In 2004, the Food and Drug Administration banned ephedra. The supplement continues to be sold today, but without the active ingredient (alkaloid) ephedra.

Instead, products are now sold with ephedra extract, which lacks the potent ingredient for weight-loss efficacy. Guarana as a stand-alone herbal substance is not proven for weight-loss efficacy.

Acai berry

Acai berry is a fruit, which like many other fruits is packed full of vitamins and minerals and antioxidants. However, it has not been proven to aid with weight loss.

Aloe vera

Aloe vera is a plant that has been used for centuries, traditionally for wounds and burns. It has laxative properties and at high doses can cause serious side effects. Manufacturers often tout its use as a weight-loss treatment.

There has been one short-term double-blinded randomised controlled study conducted in humans. Despite a significant difference in weight loss between the Aloe vera and placebo group (favouring the Aloe vera group) at the end of the eight-week study, the weight loss achieved by the Aloe vera group was not clinically significant (-0.4kg weight loss versus 0.2kg weight gain for the placebo group).

Caffeine

Caffeine is found in the leaves and fruits of specific plants. It is a stimulant and excessive consumption can cause short-term increases in blood pressure and heart rate. Caffeine increases the amount of energy we burn at rest and increases fatty acid turnover, but most of the mobilised free fatty acids are converted back to their storage form and clinically meaningful weight loss is not achieved.

Studies conducted in humans offer little evidence that caffeine by itself aids in clinically meaningful weight loss.

Ginseng

Ginseng is a plant tuber native to eastern Asia and North America. As with plenty of other weight-loss products, it has shown potential and efficacy for weight loss in animal models but has not yet been proven to work in humans.

It is being investigated in a double-blinded randomised controlled trial at the University of Sydney.

Green tea

Particularly popular for its supposed fat-burning properties, green tea is believed to increase the activity of noradrenaline in the body, a hormone responsible for increasing blood pressure and heart rate. Its active component for achieving weight loss appears to be attributable to catechins, an antioxidant.

Several studies have demonstrated its effectiveness in achieving some weight loss (although not clinically meaningful). A review in 2009 looking at all human studies conducted with green tea supported this claim.

It was estimated that people having green tea achieved a 1.3kg greater weight loss when compared to those taking placebo. A greater effect was seen in Asian versus Caucasian populations, and also in those who have lower intakes of caffeine each day.

Its efficacy appears to be associated with drinking green tea rather than taking it as an extract or supplement. If you’re interested in taking a complementary product to assist with your weight loss, this may be a suitable option and an easy thing to incorporate into your routine.

Guar gum

Guar gum is a fibre derived from the seed of the guar bean. A review of guar gum looking at 11 randomised controlled trials for weight loss showed no benefit versus placebo. Usually large quantities of fibre are required to achieve efficacy, which often comes with gastrointestinal side effects. Tests are underway to address this issue.

Chitosan

Chitosan is a sugar derived from the hard outer shell or skeleton of a shellfish. A review conducted in 1998 of five randomised controlled trials in humans showed those taking chitosan achieved a 3.3kg greater weight loss than those taking placebo. However, all of the studies included in this review were published in the same journal and accompanied by a reduced energy diet, which may have confounded the results.

A more recent review showed a mean 1.7kg greater weight loss when taking chitosan versus placebo.

Since then, some well-conducted randomised controlled trials questioned this potent efficacy, showing much smaller weight loss results (-0.4kg weight loss for chitosan group and +0.2kg weight gain for placebo group).

Cayenne pepper

Also known as red hot chilli pepper or red pepper, cayenne pepper is prepared from ground dried chilli peppers.

Research has shown it to increase the amount of calories we burn at rest (approximately ten more calories burnt over a four-hour period), but its individual (stand-alone ingredient) application in the treatment for weight loss is not proven.

White bean extract

The common white bean (Phaseolus vulgaris) produces a substance that inhibits particular proteins (alpha-amylase). This substance is the active ingredient tested in numerous clinical studies. A review conducted in 2011 estimated a 1.8kg greater weight loss with consumption of this extract relative to placebo, but several methodological flaws in the studies conducted with such a product make it difficult to draw any firm conclusions. These included studies of very short duration with small sample sizes.

As with green tea, this may be a suitable complementary medicine to assist with some short-term weight loss, but does not appear to be of clinical significance.

Eucommia leaves

Eucommia leaves and bark come from the tree Eucommia ulmoides. The supplement has been tested in animal models and shown to increase stimulation of brown adipose tissue (highly metabolically active), but its efficacy for weight loss in humans is unproven.

If there is to be a role for complementary and alternative weight-loss products we need to build upon the evidence to investigate whether these increasingly popular products are a viable treatment option. Most importantly, the composition of each product varies between manufacturers. Therefore it is important to buy the specific product with proven efficacy and safety.

If you live in the Sydney metropolitan area and would like to find out about participating in clinical research, please email clinicaltrials.boden@sydney.edu.au