Relying on a smartphone-based strategy to lose weight may be the wrong call, a new study finds.

After a two-year trial, young adults (aged 18 to 35) who used one of two phone-centered methods to trim their waistlines fared no better at chucking the chub than a control group—who received three handouts on exercise and healthy eating. The findings, reported in the journal Obesity, cast doubt that popular weight loss apps will alone offer significant help in curbing health problems in this vulnerable age group, the authors concluded.

A little over a third of young adults are obese, the authors note. And weight gain in this age window can set people up for lifelong health battles, including a 20-fold higher risk of developing a metabolic syndrome, which can lead to diabetes and cardiovascular disease.

Yet, this tech-savvy age range may be primed to extract the maximum health benefits from mobile and app-based diet and exercise plans—at least more so than the middle-aged crowd, which has been the primary focus of other weight loss studies. In those studies, successful behavioral weight loss methods included regular sessions with a personal interventionist, such as a dietitian. For obesity treatment, health experts recommend 14 or more sessions over a six-month period for the best results.

To see if mobile devices could guide a younger crop of dieters to a thinner future, researchers, led by clinician Laura Svetkey at Duke University, designed a trial of two smartphone-based methods. The first was a weight loss app, designed by the researchers, that offered health interventions and monitoring. The app featured goal-setting, challenge games, and social support through an in-app “buddy system” of trial participants. The app helped participants track their weight, food, and physical activity.

The second phone-based method paired participants with a dietitian coach for six weekly group sessions that were followed by monthly phone-based check-ins. The participants could also use a phone app to track their weight, food intake, and exercise. That data was then transmitted to the interventionist.

At the start, the researchers randomly sorted 365 overweight or obese young adults into one of the two groups or a control group that got handouts. (Those in the phone-based groups got Android smartphones.) And the researchers checked in with everyone at six, 12, and 24 months. Though some participants dropped out during the trial, more than 85 percent stayed in, leaving each group with a bit over 100 participants.

During the trial, both phone-based groups participated in their plan. In the app-only group, participants interacted with the app an average of 4.6 times a day for the first six months and 0.7 times a day in the final year. In the group that got a coach and an app, participants used the app an average of 1.8 times a day for the first six months, and went down to 0.4 times a day in the last year.

But, despite the solid participation, the phone-based methods didn’t significantly help either group lose more weight than the control group after two years. Each group's average weight losses hovered around one or two kilograms. The group with a personal coach started out strong, with a mean of 3.07 kilograms of weight lost in the first six months. But by 24 months, their waistlines were not significantly trimmer than the control group’s. The app-exclusive group’s weight loss was not significantly different from that of the control group throughout the whole trial.

The trial's result “sounds a cautionary note concerning intervention delivery by mobile applications alone,” the authors concluded. They called for more research to see if apps could be optimized or bundled into personally tailored and/or multi-pronged weight loss plans.

Obesity, 2015. DOI: 10.1002/oby.21226 (About DOIs).