Researchers writing in the Archives of Internal Medicine found that overweight and obese adults lost an average of over eight pounds (3.6 kilograms) more when they had personal digital assistants (PDAs) and occasional phone coaching to help them, in addition to a group programme.

There’s no reason to think the same wouldn’t hold true for smart phone apps that can log nutrition and activity information, and give real time feedback, they said.

"The number one mechanism through which people lost weight is self–monitoring, just watching what you eat and keeping a record of it," said Goutham Rao, who wrote a commentary published with the new study.

Rao, from the NorthShore University HealthSystem in Evanston, Illinois, noted that programmes for mobile devices are easily personalised, and readily available wherever people carry their phones or PDAs. "I’m actually very optimistic that people who are motivated, who can couple the technology with in–person counselling and management, are going to be very successful," he said.

The study included 69 overweight and obese people in their late 50s, on average, who were referred to a Veterans Affairs clinic for weight–loss support.

All were enrolled in 12 group sessions over six months, which focused on nutrition, exercise and behavioural changes to promote weight loss. Half of them were also given a PDA to record their food and activity throughout the day and had a coach who checked in with them by phone.

After six months in the trial, people in the PDA group had lost an average of almost 10 pounds (4.5 kg) and 41 per cent of them had met the goal of losing at least five per cent of their initial body weight. Those in the comparison groups had dropped just over two pounds (1 kg) each, on average, an 11 percent had achieved the weight loss goal. At the one–year mark, six months after the mobile devices were taken away, people who’d used the PDAs had managed to keep off most of the weight they initially lost, said lead researcher Bonnie Spring, from the Northwestern University Feinberg School of Medicine in Chicago.

The benefits of using an app on a mobile device, Rao said, are that it can be cheaper and widely available, and can help re–engage people who are having trouble, unlike an in–person programme with a specific end date. Although PDAs have mostly fallen out of fashion, the researchers said smartphones can serve the same purpose as the devices used in the study. Spring said most weight–loss apps on the market haven’t been scientifically tested but may still help people lose weight. Still, Rao warned, there’s evidence that apps alone don’t have much of an impact and it may be more helpful to think of the technology as an aid to help from a doctor or nutritionist.