Berberine: bad medicine? (Image: Shibai Xiao /naturepl.com/Alamy)

Easy weight loss always comes with a catch. A widely taken plant extract has helped obese mice burn off the calories without exercise – but there are concerns over its safety.

The fight against obesity gained ground in 2009 with the news that our bodies carry small deposits of brown adipose tissue – a type of fat that burns calories by turning energy into heat. Since then, researchers have been looking for ways to ramp up brown fat activity to realise the dream of weight loss without exercise or counting calories.

Enter berberine. A plant extract found in many Chinese herbal medicines, it has been linked to reductions in insulin resistance in animals. Guang Ning at the Shanghai Jiao Tong University School of Medicine have now shown that it helps weight control in obese mice by both activating brown fat and helping turn ordinary white fat brown.


Weight control

Ning’s team gave the mice berberine every three days for a month. Scans showed that the brown fat between the rodent’s shoulder blades burned more calories than that in mice not given the extract. There were also signs that the white fat in their groin had begun to act like brown fat. As a result, the mice fed a high-fat diet had better control over their weight.

It’s a top quality bit of research, says Henri Huttunen at the University of Helsinki in Finland. “It nicely brings together some earlier isolated findings in a comprehensive package.”

Whether berberine can help obese people control their weight is a different matter, though. There’s been a lot of hype over the promise of brown adipose tissue, says Dominique Langin at the Institute of Metabolic and Cardiovascular Diseases in Toulouse, France. “But it remains true that adult humans, even lean ones, have much lower brown adipose capacity and ‘browning’ capacity than rodents.”

Toxic to rodents

This might not stop people with obesity from taking berberine, though. “My understanding is that there are hundreds of thousands, if not millions of people who use berberine,” says Huttunen. That might be a bad idea, though. A few weeks ago, Huttunen’s team published a paper in which they detail evidence of a link between the supplement and toxicity in the central nervous system of rodents, which raises concerns about its safety for human use.

“If this was a pharmaceutical we would begin by showing it’s safe and then looking at efficacy,” says Huttunen. “But because it’s a supplement there’s much less concern about the safety – which I find a bit disturbing.”

Ning points out that people have been taking berberine in China for 2000 years but agrees it’s imperative to test its safety profile. “Toxicology must be studied for the long-term application in obesity treatment”, he says.

Journal reference: Nature Communications, DOI: 10.1038/ncomms6493