Can an calorie-tracking app on your phone help you lose weight? Not if you don't use it -- at least that's the conclusion of a new study.

Researchers recently looked at usage of the popular smart phone app MyFitnessPal, which tracks meals and calories and integrates with wearable fitness trackers like Jawbone's UP band. They split 212 primary care patients with body mass indexes of 25 or greater (a BMI above 25 is considered overweight; above 30, obese) into two groups. One group received normal care; the other was given a version of the MyFitnessPal app.

Six months later, the researchers measured weight loss, among other baseline health measures like blood pressure. The verdict: There was little difference between the groups; nor did anyone lose much weight.

If you read the current headlines for this study, you might be left with the impression that such technology are not very much helpful weight loss tools -- and indeed the authors say that just "introducing a smartphone app is unlikely to produce substantial weight change for most patients."

File this one under "well, duh." Weight loss takes more than a gizmo; it takes a conscious effort, and while the tools that aid you are great, they don't work so well without commitment. They especially don't work well if you don't use them. Many of the participants in the study didn't really use the app, even though they reported liking it. "Logins decreased sharply after the first month," the study's authors reported.

But keeping track of food intake helps with weight loss, whether on paper or through apps. Dozens of studies back this up. 

Even the authors of the current study concede this point, concluding, "Smartphone apps for weight loss may be useful for persons who are ready to self-monitor calories."

For what it is worth, I've used MyFitnessPal off and on for the last year. My weight loss goals do best when I'm fully engaged with the app, which is a vast improvement over earlier calorie-tracking efforts and beats the heck out of lugging a journal to lunch. But does it make tracking caloric intake as easy as wearable technology makes tracking steps? Sadly, no.

If anything, studies like this one remind me that the holy grail of calorie tracking apps has yet to be invented; as good as MyFitnessPal is, the app still requires customization and time to look up foods. The right app might be a very different story.