The datafication of our health, and what we can do to fix it

We’ve turned our bodies into dashboards! So when did our watches start to know more about how we feel?

There was a time when knowing how you were doing meant knowing how you felt. A bit tired means you need to sleep, a bit thirsty means you grab some water, and having a bad day, maybe skip the gym and cuddle up on the sofa.

But in our culture of constant surveillance, our watches count our steps, calculate our calories, monitor our heart rates, and score our sleep. We can measure our resting heart rate, stress levels, and menstrual cycles before we've even got out of bed.

In essence, our health has become data. And, increasingly, we trust the data more than we trust ourselves. In PLOS One, researchers compared four popular smartwatches (Apple, Garmin, Samsung and Fitbit) with indirect calorimetry, a clinical method used to measure energy expenditure. Three of the four devices showed significant bias, while the size of the error varied between brands. Crucially, the researchers found that calorie-expenditure error increased as body-fat percentage increased.

It is not exactly breaking news that a smartwatch isn't 100% trustworthy. But the finding exposes a bigger problem with the way we've started to think about health technology, in that we see a number, and because it is a number, we assume it is a fact.

A calorie figure on your wrist is an estimate produced by an algorithm, inferred from things like movement, heart rate and personal characteristics. A systematic review published last week described energy expenditure as one of the hardest variables for wrist-worn health devices to measure accurately.

But don’t bin anything yet; your watch can be genuinely useful in showing you patterns. Maybe you sleep better when you drink less alcohol or your resting heart rate changes when you're run-down. Things worth noting, when perhaps you are feeling a bit out of your body at times, which we can all admit, it can happen at times.

Letting it become an authoritative voice on your health is where the issue lies.  This is the datafication of health, the process of translating increasingly large parts of our physical lives into measurable information. Numbers are objective, so they make tackling our health look manageable. Yet, health is messy and constantly changing. Your watch doesn't know that you stayed up late because you were celebrating your mate's birthday, and it can't quantify the pleasure of running with music you love, or the fact that your walk home cleared your head after a difficult day.

Use the data as information and look for patterns once in a while. And most importantly, ask yourself: How do I actually feel?