Yet these estimates are notoriously inaccurate: One study from the Stanford University School of Medicine compared seven different wrist-worn fitness trackers and found that the most accurate estimate of energy expenditure (in other words, calories burned) was off by 27 percent. The least accurate was a whopping 93 percent off. None of the devices provided estimates of energy expenditure "within an acceptable error range,” concluded the researchers.
This won’t come as a surprise to anyone who knows the truth about calorie counts. The food labels that tell you how many calories are in packaged foods? Those are seriously unreliable, too, because they rely on averages that don’t actually take into account how our bodies digest different foods. However, they are closer than calorie burn estimates: The Food and Drug Administration only allows inaccuracies of up to 20 percent.
So if these numbers are essentially meaningless, how did we come to accept them as a standard? And why do they have such staying power over seemingly every new piece of fit tech launched?
How calorie counting took over our brains
The history of counting calories goes all the way back to the 1800s, and it’s pretty bizarre. The calorie has existed as a measurement of energy since the 1820s, but it wasn’t originally used to measure anything in the human body. That is, until 1896, when a researcher named Wilbur O. Atwater put a graduate student inside a calorimeter, a device that was designed to measure energy generated by explosives and engines. The machine measured everything the student ate and his energy output, showing that human bodies take in and put out energy like machines—or bombs (yikes).
However, calorie counting for weight loss didn’t become popular until a couple decades later. That came about in 1918, when doctor and newspaper columnist Lulu Hunt Peters put out a book called Diet and Health: with Key to the Calories.
Needless to say, our understanding of the human body has advanced a lot since 1918. We know, for example, that the nutritional value of food goes far beyond simply an estimate of how many calories you might absorb from it. And the many health benefits of exercise are not reflected in just one number.
“People need to understand that these calorie counters are built on algorithms, and your body is not an algorithm. Your body needs specific things that other bodies don’t,” says Kerry O’Grady, national wellness liaison with the National Eating Disorders Association. Different bodies absorb and burn calories differently (and, obviously, need more than just calories). “The more we buy into these numbers, the more we’re going to stop listening to our own bodies.”
"Calorie counters are built on algorithms, and your body is not an algorithm." —Kerry O'Grady
For her, it’s personal. “I lived this,” she says. “I almost died from anorexia in my early 20s. I can’t use a tracker because it’s very triggering for me.”
That’s not unusual. Experts typically suggest that anyone with a history of disordered eating, orthorexia, or obsessive habits around exercise and nutrition steer clear of fitness trackers. Even those without such a history might find that trackers make healthy habits less fulfilling. “Quantifying everything takes away a lot of the joy around movement and food,” says personal trainer Lauren Pak. “It makes exercising and eating feel clinical, like a job.”
Some of us can look at calorie counts and ignore them, but many people are more affected than they realize. “I think that the hardest part about breaking up with calorie counting is that many of us who have some experience with it might be able to stop tracking, but the calorie data lives rent-free in our brains,” says Jessi Haggerty, RDN, a certified intuitive eating counselor and personal trainer. For example, if you feel like you aren’t allowed to “indulge” in certain foods on days you haven’t exercised, you may not have done the exact math, but you’re still thinking about nutrition and exercise in a way that’s shaped by calorie counting.
And that idea you have of how many calories you need in a day? It’s probably wrong, says Rena Eleázar, DPT, a physical therapist, sports performance coach, and competitive weightlifter. “Almost across the board, athletes I work with have this illusion of how many calories they’re expending, and they’re usually under-eating,” she says.
A double-edged sword
Wearable devices and connected devices can help some people stay consistent with a workout routine, and remind them of their goals. And some of the data that trackers collect can be helpful. For instance, heart rate info can help with highlighting exercise intensity and monitoring safety for some people with chronic health conditions. Other measures, like heart rate variability, can give you useful information about how well you’re managing stress, both physical and mental.
But the ubiquity of calorie counts on fitness trackers make diet culture hard to escape. “What is and isn’t helpful is very person-dependent,” Pak says. “You should be able to choose what you want to track. It shouldn’t be assumed that people have a weight loss goal attached to a fitness endeavor.” With some systems, you can essentially game your way out of calorie counts by not entering your weight; others will still display an (even more bogus) number of calories by automatically subbing in an “average” weight.
Counting calories simply isn’t a good way to learn what your body needs, and can cause you to restrict what you’re eating in a way that quickly becomes unhealthy, says Haggerty. The only situation in which tracking calories might be useful, she says, is for people who are struggling to eat enough to keep up with their training, a common problem among endurance athletes. “Even so, there are ways of doing that that don’t require tracking,” she says. If you’re having trouble figuring out what or how much you need to eat, Haggerty suggests working with an anti-diet or Health at Every Size-aligned dietitian. Good rules of thumb for people who are training hard, she says, are to aim for three meals and three snacks each day, and to eat within an hour of exercising.
So why do digital devices still include calories?
Most digital fitness companies contacted for this story did not want to comment on the record, though some confirmed that they do see a consumer demand for calorie burn estimates. “They’re ubiquitous because people want them,” says O’Grady. “If the market did not demand them, they wouldn’t be there. Even though so many people know those numbers are inaccurate, they’d be upset if they were removed. That’s what these tech companies are banking on. They want you to have a relationship with that number.”
Diet culture is so deeply ingrained in so many of us that we can’t mentally uncouple calories and exercise—even when we know better.
So, does that mean you need to break up with your fitness tracker? If you’re finding yourself paying more attention to the numbers on screen than to how your body actually feels, maybe. “You can pretty much gauge how well your nutrition is going based on how you feel in the gym,” says Eleázar. If you’re exhausted during every workout, that’s a sign that something needs to change, and it’s very likely you need to eat more. Trust that sense of your own body over any tracker.
And even if you're set on tracking your workouts, don’t underestimate the benefits of going analog. You can always use an old-school pedometer to count your steps, or grab a stopwatch to time your intervals, for instance. “I think that just writing down the details of your workout is great,” says Pak. “Then you can track the progress you made from week to week. Maybe this week you did three sets of 10 squats with 25 pounds, and next week you do three sets of 10 with 30 pounds. That’s great progress.”
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