First anti-obesity electronic implant wins US approval

by Clare Wilson

From crash diets to stomach-stapling and jaw-wiring, it seems there's nothing people won't try to lose weight. Soon you may even be able to have an implant, one that works by blocking signals between the stomach and the brain.

The device, called the Maestro Rechargeable System, has just been approved by the US Food and Drug Administration for people who are both severely obese – defined as those with a body mass index over 35 – and have a weight-related condition such as diabetes. Once fitted, it is recharged and adjusted wirelessly using an external controller. It is due to go on sale in the US later this year, with sales in other countries to follow.

The device doesn't seem to be the long-sought cure for obesity, though, as it leads to only modest weight loss – about 9 per cent. That compares with a 6 per cent weight loss in people who had a sham operation, in which the device was fitted but the electrodes were not connected.

Bypass or no?

"That's not a game changer," says Nick Finer of University College Hospital in London. If people are going to have surgery they would be better off having a gastric bypass, he suggests, which leads to greater weight loss. "It's extremely safe and durable."

However, obesity surgeon Scott Shikora, speaking for the device's manufacturer, EnteroMedics, says that some people dislike the idea of having their intestines "replumbed". "A lot of patients don't want the operations we are currently performing because they view them as being too risky or too radical," he says.

In a year-long trial of the Maestro system in 239 people, there were few serious side effects. But people who got the real implant were more likely to have indigestion, abdominal pain or nausea.

The company has not yet published the results of longer-term trials. But Shikora says one of these, smaller than the year-long study, suggests people's weight loss seems to plateau after about a year but is maintained for at least five years.

Vagus nerve

The signals blocked by the device travel along the vagus nerve, an important line of communication between the brain and several major organs. The electrodes wrap around the branch of the nerve connecting to the stomach. This contains both the neurons going from the stomach to the brain and those going back down to the stomach.

According to EnteroMedics, blocking this signalling pathway reduces stomach expansion and contraction, as well as the secretion of digestive enzymes. The net result is that people feel less hungry and their calorie intake is reduced.

"There's a treatment gap between diet and exercise and conventional surgery," says Shikora. "This would fit nicely between the two."

Other conditions can be treated by devices that stimulate the vagus nerve. A neck implant is used to reduce seizures in people with epilepsy, for instance, and a similar approach is being investigated to treat headaches, depression and tinnitus.