Your Wearable Device Won’t Do the Thing You Desperately Want it to Do

Wearable devices are all the rage. When you have one, like an Apple Watch or a Fitbit, it tells the world that you care about your fitness. But if weight loss is your goal, a new study shows that you may be better without one.

Although previous studies have shown that activity trackers may help you lose weight, they only observed the experimental subjects for six months or less. John Jakicic and his colleagues at the University of Pittsburgh’s Physical Activity and Weight Management Center wanted to know what activity trackers do to people’s weight over a longer period.

They recruited 471 men and women between the ages of 18 and 35 for a 24-month randomized clinical trial. First, all subjects were put on a six-month low-calorie diet. The participants lost, on average, 8kg (17.7 lb) in that period.

Next, the group was randomly split into two. One group was asked to log their daily exercise on a study website. The other group was given an activity tracker worn on the upper arm. Like other commercial activity trackers, this would give the users feedback on whether they were achieving their step goals and burning enough calories.

The hope was, as previous studies had shown, the group wearing the activity trackers would be more conscientious than the group that didn’t wear them. But at the end of 18 months, they got the exact opposite results.

Both groups put on weight in the aftermath of the diets, whether they had activity trackers or not. But those who wore activity trackers were 4.5kg heavier than when they ended the diet, compared the people who had not worn activity trackers, who were, on average, only 2kg heavier.

John Jakicic was surprised by the results and does not yet know for sure why activity trackers didn’t work as expected. There are two possible hypotheses.

It may be that those who wore the activity trackers did exercise more, but to compensate they also ate more and thus gained more weight back. But the data doesn’t support this hypothesis, because those wearing activity trackers exercised less than the group that was self-reporting their exercise sessions.

So perhaps it was that the continuous feedback from the activity trackers backfired. When users realized they won’t achieve their activity goal, they just gave up. “People may have focused on the technology and forgotten to focus on their behaviors,” Jakicic told the New York Times (paywall).

There are limitations to the study. The subjects were all young, which means the conclusions may not be applicable to people of other ages. They also started using activity trackers after having gone through a diet program, which may have altered their behavior compared to those who have never tried a diet before.

Finally, the activity tracker was worn on the upper-arm compared to the more convenient trackers worn on the wrist. That inconvenience meant the activity tracker was worn by the group for a median of 170 days, which is only a third of the 18-month period. It’s not clear whether wearing them every day would’ve made a difference to the results.

Still, it’s interesting to find out that people’s reaction to technology may not be what we expect—especially when devices like the Apple Watch Series 2 focus so heavily on fitness. Jakicic is conducting follow-up studies to find out how activity trackers affect people’s motivation and exercise goals.