The CITY Android app used in the Duke study.

Duke University published a study in the journal Obesity this week which shows that, over a two-year period, neither a specially designed mobile app nor a coaching intervention that utilized a mobile app was any more effective in promoting weight loss than the control intervention -- a handful of fliers from a doctor visit.

“For some people it did work,” lead author Dr. Laura Svetkey said in a statement. “But on average, the difference with the control group was insignificant. This doesn’t mean cell phone apps can’t work for weight control, but this one didn’t.”

The study was particularly interesting compared to other weight loss studies for a few reasons. For one thing, it evaluated longterm weight loss outcomes, over two years. For another, it focused on 18- to 35-year-olds, a group that is often overlooked for weight loss despite the fact that weight gain is most rapid during these years and, according to studies, predicts future cardiovascular events.

"Thirty-five percent of this age-group is overweight or obese, and that’s a huge public health problem,” Svetkey said. “We thought that because this is an age group that is most engaged in technology, it might be possible to intervene and prevent future problems like cardiovascular disease, high blood pressure and diabetes while they are still developing their lifestyle habits.”

Study authors still aren't quite sure why that didn't happen in this 365-participant study. Overperformance by the control group might be part of the problem -- whereas control groups normally gain a small amount of weight during these studies, this one lost 2-3 pounds. It may have been down to the design of the app itself which, unlike commercial weight loss app, wasn't able to iterate in response to patient feedback. It's also possible that the data was made muddy by participants in all groups using other commercial weight loss apps. But researchers asked participants about other apps in a follow-up interview and found no significant difference in the control group between those who used outside apps and those who didn't.

The study did find that the arm which used in-person coaching interventions supported by app-based tracking was able to produce statistically significant weight loss at six months, but after a year that weight loss wasn't sustained.

“A lot of people can lose weight in a short amount of time,” Gary Bennett, another senior author on the study, said. “The real question is, can they keep it off in the long term? Research has really focused on older populations, and that’s a missed opportunity. We know that younger consumers are a population that we’re having an extraordinarily difficult time treating, and who need intervention now to offset health risks later on.”

Weight loss apps are some of the most popular and ubiquitous health apps on the iOS and Android app stores, but there isn't yet too much data that supports their effectiveness. This study shows why it's important to see that data.