There is insufficient evidence to justify recommending herbal and dietary supplements to help people to lose weight.
That is the emphatic view of researchers who will present studies on the effectiveness of supplements at the European Congress on Obesity (ECO) to be held online this week.
“Even though most supplements appear safe for short-term consumption, they are not going to provide weight loss that is clinically meaningful,” said lead author Erica Bessell of the University of Sydney in Australia.
Herbal supplements contain whole plants or combinations of plants, while dietary supplements contain naturally occurring single compounds. They can be purchased as pills, powders and liquids and have become increasingly popular as aids to losing weight.
One recent estimate has suggested that 15% of Americans have tried a weight-loss supplement in an industry worth $40bn (£29bn) worldwide. Yet there have been few recent attempts to review the scientific literature on all available herbal and dietary supplements.
Herbal supplements include green tea, white kidney beans, ephedra (a stimulant that increases metabolism), African mango, yerba mate (a herbal tea made from the leaves and twigs of the Ilex paraguariensis plant), liquorice root, and others.
To study the effectiveness of these supplements and others, the Australian researchers did a systematic review of all previous randomised trials in which the weight-loss impact of herbal supplements were compared with the impact of placebos. Data was analysed for 54 studies involving 4,331 healthy, overweight or obese adults – and revealed that only one single agent, white kidney beans, resulted in a statistically greater weight loss than a placebo.
In a separate study, the group analysed previous trials that compared the effect of placebos with dietary supplements that included chitosan (made from the hard outer skeleton of shellfish); glucomannan (found in the roots of the elephant yam, or konjac); fructan (a carbohydrate composed of chains of fructose); conjugated linoleic acid (which claims to change the body composition by decreasing fat); and others.
Analysis found that chitosan, glucomannan, and conjugated linoleic acid resulted in weight loss but not at levels that were clinically significant. In addition, some other dietary supplements – including modified cellulose (a plant fibre that expands in the stomach to induce a feeling of fullness) and blood orange juice extract – showed promising results but had only been investigated in one trial. Much more evidence was needed before they could be recommended as aids for weight loss, the researchers concluded.
“Herbal and dietary supplements might seem like a quick-fix solution to weight problems but people need to be aware of how little we actually know about them,” said Bessell. “Very few high-quality studies have been done on some supplements, with little data on long-term effectiveness.
“What’s more, many trials are small and poorly designed, and some don’t report on the composition of the supplements being investigated. The tremendous growth in the industry and popularity of these products underscores the urgency for conducting larger, more rigorous studies to have reasonable assurance of their safety and effectiveness for weight loss.”
Vegetarians less prone to disease
Vegetarians appear to have healthier profiles for disease than meat-eaters, according to a study in over 166,000 UK adults, which will be presented at this week’s European Congress on Obesity.
“Our findings offer real food for thought,” said Dr Carlos Celis-Morales from the University of Glasgow, who led the research. “As well as not eating red and processed meat, which have been linked to heart diseases and some cancers, people who follow a vegetarian diet consume more vegetables, fruits and nuts, which contain more nutrients, fibre and other potentially beneficial compounds.
“These nutritional differences may help explain why vegetarians appear to have lower levels of biomarkers that can lead to cell damage and chronic disease.”