And the new weapon in the fight against the battle of the bulge is — a cell phone? Yes, in a recent study, people who used an experimental cell phone app in addition to joining a weight-loss program lost an average of 8.6 pounds more than the other people in the program did. Those who used it consistently also lost more weight over a full year, beginning to end.

The app keeps track of how many calories a person is consuming and how much exercise they're getting, and it also transmits this information to a weight coach who provides individualized guidance after looking over the info. The coach also helps with any technical difficulties people might be having using the app.

Three months in, about one-third of the group with the devices had already lost 5% or more of their body weight, while the group who received no calls had no weight loss at all.

Northwestern University researchers recruited 70 overweight and obese people. All 70 participants took part in the MOVE! group weight-loss program offered at all VA medical centers. Each session was led by a dietician, psychologist or doctor and lasted approximately 1.5 hours. Sessions included discussion of nutrition, physical activity, and behavior change. Participants were weighed at each session and encouraged to monitor themselves, but received no personalized feedback. For the first six months of the study, participants met twice a month; during months 7-12, sessions were monthly.

Half of the people were given a smartphone-like mobile (PDA) device and app specially built for the study and designed to be easy to use, even by those who were not tech savvy. Over the first six months of the study, they received, on average, eight personalized phone calls of about 15 minutes each from their weight coach. During the second six months they received no telephone coaching; a coach called only if people stopped sending in data on the PDA.

All participants were weighed at 3, 6, 9 and 12 months. Those who used the PDA had better results at all time points. Three months in, about one-third of the group with the devices had already lost 5% or more of their body weight, while the group who received no calls had no weight loss at all. The PDA group averaged 8.6 pounds more weight loss at all four weighings.

The app isn't a magic bullet. What it does is make a weight-loss program work better. People who attended at least 80% of the MOVE! sessions lost an average of 15 pounds over the year. But people who attended fewer than 80% of the sessions actually ended up gaining weight.

The study was published online in Archives of Internal Medicine and will also appear in a future print issue of the journal. The article is freely available.