Activity Trackers Aren’t A Weight Loss Miracle Cure

Wearables like activity trackers do get a bit of attention today. They are still a bit gimmicky as the market is still figuring out how people use them and want to use them. But there is a steady uptake in their usage, consumers bought a respectable 78 millions devices last year. I’m even among the folks who quite happily use a fitness tracker to track exercises and keep an eye on their health.

The detail though is that these type of devices haven’t been around for long. Fitbit, probably one of the more known brands, introduced their first activity tracker in 2009. That’s not a lot of time to gather data on how they’re used and how effective they are. Which is a bit of a problem when you’re making health claims about these devices.

It does sound very plausible that an activity tracker can help you with shedding some excess weight. They can, among other things, give you reminders for exercises. Fitbit also has a blog full with success stories. Same for Garmin’s site (bonus points for mentioning a naturopath), JawBone, or on the Polar website. All these success stories are probably at the root of the idea that you can use activity trackers to fight obesity.

But How Effective Are Activity Trackers?

The detail is that the success stories on websites are often from highly motivated people. This motivation is at the root of why they’ve been successful. Plus it’s a skewed representation as you don’t promote the people who don’t succeed or who don’t get spectacular results.

So when the paper Effect of Wearable Technology Combined With a Lifestyle Intervention on Long-term Weight Loss: the IDEA Randomized Clinical Trial popped up on my radar it had my full attention. This was a randomized clinical trial that tracked people for two years. During that time the set up of the study was as follows:

Participants were placed on a low-calorie diet, prescribed increases in physical activity, and had group counseling sessions. At 6 months, the interventions added telephone counseling sessions, text message prompts, and access to study materials on a website. At 6 months, participants randomized to the standard intervention group initiated self-monitoring of diet and physical activity using a website, and those randomized to the enhanced intervention group were provided with a wearable device and accompanying web interface to monitor diet and physical activity.

The results of this were a surprise for me, despite me being skeptical about the success stories. The people in the group that didn’t use an activity tracker lost on average 5.9kg during the two years this study ran. Those wearing an activity tracker lost 3.5kg during the same period. The group without wearable tech lost on average 2.5kg more.

Colour me surprised. I though it was a matter of overselling the devices. I didn’t expect them to hinder your weight loss. There are also no differences between the two groups that would explain why one group lost less weight loss. On this the paper says:

Both groups had significant improvements in body composition, fitness, physical activity, and diet, with no significant difference between groups.

What’s Going On?

This does seem like a bit of a head-scratcher. There are a lot of success stories claiming that using an activity tracker helped with getting spectacular results. Kinda hard to argue with the before and after pictures. At first glance it does seem plausible as the activity tracker I have sets goals, has training sessions, gives me reminders, deals out badges and rewards for achieving goals, tracks calories in and out, and encourages competition among friends.

The researchers aren’t sure why there was such a stark difference between the two groups. Short term studies did find, according to the researchers, that using an activity tracker caused “modest improvements in weight loss when added to a behavioural intervention.” Though these short-term studies often have a small group of participants. They also note that there isn’t a lot of data on the long-term usage of these devices. Making it difficult to draw any conclusions as to why they found such a stark difference between the two groups.

Though I have hunch as to what might be going on: it’s most likely behaviour. A point the researchers highlight for further study to figure out this played a role and how big a role. But before I dive into the behaviour angle you’ll need some context that the video below provides.

Exercise is NOT the Key to Weight Loss

It might be behaviour

Most people tend to think that exercise is far more important for weight loss than restricting the amount of calories you take in. But to burn 300 calories I need to spend about 30 minutes on a home trainer. If I don’t drink two cans of sugary soda I can remove just as many calories. You can imagine which one is easier to do.

Fitbit exercisesWhat then contributes to this is that people also have a tendency to overestimate the amount of calories they save by for example switching to lite versions of a product. They end up eating more calories as the thinking then is that you can now eat more while still eating fewer calories.

But those aren’t the reasons what I think are at the root of the problem here. They illustrate some of the mental processes about how people think about weight loss, exercise, and diet. What I suspect is happening here is that the participant that wore the activity tracker were too aware of the calories they were burning.

My activity tracker watches my heart rate and movements and it uses that to calculate how many calories I’m burning. This means that my activity tracker can count normal daily activities as exercises. For example I have the tendency to walk around when I’m on the phone. As you can see in the image to the right my activity tracker recognised that as an exercise and said I burned 92 calories.

Same goes for stairs, walking around in a mall, or any sort of household chore. Suddenly these calories are visible to you and now you’re aware of the extra calories you can eat. But we’ll need follow-up studies to figure out if this is the cause for the difference the researchers found and to what extent it contributed.


The researchers couldn’t answer why participants with an activity tracker lost less weight than participants without one. There are limits in the study that the researchers say might have introduced some biases. One of them being that assessment staff knew that participants were participating in a weight loss trial.

Which could be a hint about why participants lost so much weight. For both groups it was more than you would normally expect (2kg versus the 8kg achieved in this study). Also participant wore the activity tracker around their upper arm. This could mean that the results in this study can’t be directly compared to the results you’ll get from an activity tracker that you wear around your wrist.

We’ll need to wait for further studies to hone in on what precisely is going on and how this translates to the devices that are in use. But this study, combined with the short-term studies, already gives a good indication that activity tracker weight loss claims are being oversold.

Collin Maessen is the founder and editor of Real Skeptic and a proponent of scientific skepticism. For his content he uses the most up to date and best research as possible. Where necessary consulting or collaborating with scientists.