If there’s one thing my baseball- and golf-obsessed father and I have in common, it’s our love for stats. While my dad recaps his game hole-by-hole at the golf course, I supply my own rendition of a course play-by-play, reporting details from every mile of a 26.2 during our phone calls (he’s a good dad).
Someone, er, something else that is also receptive to my run data: my Garmin, which acts as a record keeper and virtual cheerleader. Do I feel just a little better about myself after I read my morning report’s sleep score, HRV, and recovery status followed by one of only five affirmations? “Be your best today!” reads my watch face. Oh, I will, Garmin. I will.
However, there is one number on my wearable that I’m wary of: calories.
For me, tracking caloric expenditure is a slippery slope. As the typical Type-A runner, I’ve experienced the unhealthy “come hell or high water” approach to following training plans, obsessing over weekly mileage, and counting calories. My aversion to looking at calories burned is for my mental wellbeing.
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Not Every Calorie Is Created Equal
One fitness mantra dietitians, including Doane, continue to squash is “calories in, calories out.”
“‘Fewer calories will always result in less body fat’ kind of negates or doesn’t account for all the body processes that are going on,” said Doane on a phone call. “If you’re just looking at it as ‘calories in, calories used,’ it doesn’t take into account the fact that every calorie we burn isn’t the same. For example, we burn fat but we also use up glycogen or stored carbs. It kind of just lumps calories into one bucket. Instead, it is really a ‘fueling and sports nutrition’ type of equation, versus just a math equation.”
It Begins With BMR
Before we get into calories burned, we have to start with BMR. Your basal metabolic rate is the number of calories your body needs to perform its daily life-sustaining functions. Every individual has their own BMR. When athletes deprive themselves of calories, they put both their athletic performance and healthy organ function in jeopardy.
“Could someone eat 1,000 calories a day if they needed 1,500 to live?” said Doane. “They can, but their brain thinks slower, their heart rate’s slower, their digestion’s slower. Their body might not heal as fast. All of the functional things the body does with proper nutrition just get lost in the mix. The body can’t do all those jobs. It does not go, ‘We have less fuel, so we’ll just burn fat to make up for it.’ The body can only do so much with a negative calorie balance.”
Doane explains there are predictive equations to determine your BMR, but she considers them “scientific guesstimations.” A person’s gender, age, and weight could be put into a formula but these weight-based equations, she said, have a little bit more room for error. Factors like lean body mass, which provides a more accurate measurement, are left out. Doane recommends going to a practice, like a dietitian or sports medicine center, for a valid BMR.
How Does Your Wearable Estimate Calories Burned?
Health - Injuries Garmin Forerunner 955 Solar I use, estimate energy expenditure (EE) utilizing the wearer’s heart rate data, respiration rate, oxygen consumption, and the personal information you enter (gender, age, height, and weight).
VO2 max, or the maximal oxygen uptake an individual needs to perform aerobic work, is a metric used in determining EE. Ideally, VO2 max would be collected in a laboratory setting. Smartwatches, like Garmin’s, use the personal information you provide plus your heart rate and speed of the activity (for exercise like running or walking). Accuracy of this method has its limitations because of outside variables, such as the type of terrain you’re running on and the amount of wind.
Apple offers up this advice for more accurate data: keep your personal information—gender, height, weight, age—up to date; check the fit For testings sake, I briefly kept track of my calorie expenditure on my Forerunner 955 and Give A Gift.
For testing’s sake, I briefly kept track of my calorie expenditure on my Forerunner 955 and For testings sake, I briefly kept track of my calorie expenditure on my Forerunner 955 and. Wearing both watches on the same arm, I slept and ran with them on, only taking off the wearables when I showered. Surprisingly, the numbers were pretty close with only an 11-calorie difference.
Can We Use This Data as a Fitness Tool?
Give A Gift—Advantage Nutrition & Wellness—Why Trust Us.
“[Calories burned data] can be a good tool to use with your provider so that they can get an insight into what intensity you’re training at,” said Doane. “But the watch still bases its equations off of what you plug in. It will put you in a metabolic-equivalent range to calculate your calories used for daily activity or a given exercise. It’s giving you a ballpark idea, but it’s never going to be super specific.”
There’s also the risk of focusing too much on EE, where you can find yourself obsessing over calories at the expense of mental and physical health and wellness. To avoid spiraling, pay attention to performance indicators and factors in your training—beyond just the numbers recorded by your watch.
Some cues that signal you’re not consuming enough calories include: headaches, dizziness, midday energy crashes, fatigue, difficulty hitting higher-intensity paces, and gastrointestinal issues.
Simply stated, listen to your body. Said Doane, “There’s no watch that can tell you what your body can.”
If you are struggling with an eating disorder and are in need of support, please call the National Eating Disorders Association Helpline at 1-800-931-2237. For a 24-hour crisis line, text “NEDA” to 741741.
Amanda is a test editor at Runner’s World who has run the Boston Marathon every year since 2013; she's a former professional baker with a master’s in gastronomy and she carb-loads on snickerdoodles.
