A question we get asked either in onboarding new clients or at the gym rather frequently is how to factor in the number of calories our smartwatch says we burned during our workout & if we should be eating back those calories in order to reach our goals.
This question often occurs because some food tracking apps have a feature in which they give you a calorie target, subtract the food you’ve logged for the day, & then ADD back your energy burned during exercise whether those calories be from a linked device or exercise you've manually inputted in the app to factor in what your remaining calories are for the day & if you’re net positive or negative.
Visually this is what it looks like...
This feature can be very confusing for some given the fact that the number of calories you burn is probably changing day-to-day even though you have a calorie target that’s consistent across the board. Not to mention the fact that the number of calories you burn during a particular exercise is going to vary in every tracking app, fitness tracker, & smartwatch. For example, I’ve worn my Garmin & a Whoop all day, doing the same workouts, the same amount of non-exercise activity & have gotten two totally different results for total caloric expenditure. My Garmin told me I burned 2,687 calories & the Whoop said I burned 2,178.
Pretty different, right?
Now, if I was using my watch/fitness tracker to determine how many calories I should eat that day, how would I choose which calorie total to eat for the day?
There wouldn't be a conclusive answer here. I could go either way. However, most people are going to go with the device that gives them more calories.
Should I eat back the calories I burned during my exercise activity if I already have a set calorie target?
Don’t get us wrong, the technology for smartwatches has come a very long way & we think they’re great tools for assessing heart rate, steps, & running splits. However, as far as energy expenditure goes, smartwatches & fitness trackers are pretty inaccurate.
And in today’s blog, we’ll be diving into why this is the case, how you can interpret the data your smartwatch is giving you, as well as give you a better way to estimate how much you should be eating per day based on your goals.
First, we’d thought we’d dive into some mindset factors around using smartwatches to assess calories burned…
One issue with smartwatches' ability to assess calories burned is that this can create a disordered relationship between food & exercise for some. This can be, in part, because some people will start looking at exercise as a way to burn calories instead of a way to improve our health & longevity, get stronger, get fitter, etc.
And trust us, we get it. It feels pretty dang good to close your rings for the day or compete with your friends at the gym to see who can burn the most amount of calories during the class workout. You get an instant dopamine response & feel validated in seeing all the hard work you just put in during your time at the gym. However, this can instill the idea that people have to exercise to “earn” their food & the more calories their Apple Watch says they “burned,” the more food they can eat. Conversely, this can give people the impression that they can over-eat & then “make up” for it by killing themselves in the gym the following day or later on the same day. Both of these mindset barriers, we’ve made one of our many Clar-e-ty missions to disprove.
Next, let’s dive into the science & data behind why fitness trackers can misrepresent our calories burned in a day & what makes them so inaccurate…
Another issue with eating back calories burned according to your smartwatch, fitness tracker, or tracking app is the inaccuracies in the algorithm they use to guesstimate your energy expenditure. One of the main errors in the algorithms fitness trackers choose to use is that it's using your heart rate to assess energy output. Meaning, that every time your heart rate elevates to a certain point, your watch is going to be computing you’re burning more calories than you more than likely are. This can also be an issue when fitness trackers are trying to guesstimate our caloric expenditure for exercise that doesn’t elevate our heart rate to a certain point or during anaerobic exercise.
For example, when you lift weights, you're using more anaerobic systems that aren't going to spike your heart rate as much as LISS cardio so your watch can't predict the energy you burn resistance training as accurately. I mean think about how much your heart is going to increase if you were to go on a ten-mile run versus if you were to do a 5x5 back squat session at a moderate to heavyweight. Your heart rate might spike during each set of your set of back squats, but then your heart rate will drop once the set is over. Conversely, on a steady-state ten-mile run, your heart rate is going to stay elevated for an extended period of time until you start your cool-down walk.
Also, your fitness tracking is missing all the metabolic adaptations that are happening in response to your workouts. When we're recovering, our tissues are breaking down & rebuilding which requires energy that's not being taken into account by your watch either. All the other work that your cells & body are putting into your recovery & building muscle aren't being taken into account because there’s no way the algorithm in your fitness tracker can account for these factors based on your heart rate alone. The only way to get an accurate reading here is in a lab & even then not all metabolism that's occurring within your body can be accounted for. That being said, your fitness tracker is missing out on everything else your body's doing throughout the day (which is a lot more to take into account than the hour you spend at the gym).
Because fitness trackers are estimating your caloric expenditure based on your heart rate & your heart increases linearly during aerobic exercise (walking, biking, running, swimming, etc.), fitness trackers are OKAY at estimating your "calories burned" during low-intensity cardio. But that doesn’t necessarily mean that you should be eating back those calories or that is an accurate representation of how much energy your body is actually burning during your walk, cardio session, or endurance-based event. It might be somewhere within the ballpark, but fitness trackers are proven to overestimate energy expenditure & output by 27.5-93% (Shcherbina et al, 2017).
This can be SUPER problematic if you were to try & eat back these calories, especially for those in a fat loss phase. In doing so, you can unintentionally put yourself in a calorie surplus by eating back the calories your watch/tracker says you've burned knowing how this number could be up to 93% inaccurate.
So going back to the question of how we figure out how many calories we “burn” daily to know how to structure our nutrition to meet those goals.
If you track your food intake tracking your food intake for 4-7 days & taking your averages for calories, protein, carbs, & fats will be a much more accurate representation of what you’re eating now to maintain your weight or to find your maintenance calories. You can then add or take from where you're currently at food intake-wise to get your desired results while taking into account your biofeedback, dieting history, metabolic history, goals, etc. This is a WAYYYY more accurate method to depict your energy expenditure than using a fitness tracker to determine your caloric intake for the day.
So what’s the bottom line here?
Your Apple Watch/Whoop/Garmin/Fitbit isn't accounting for ALL other energy systems being used in your body when your heart rate isn't elevated. Activities that also require energy like recovering, sleeping, thinking, breathing, etc. aren't being taken into account, therefore, these devices CAN NOT accurately tell you how many calories you've burned during exercise or throughout the day.
Some fitness trackers are great for tracking heart rate & steps, but not caloric expenditure & we should not be using them to determine how much we should eat throughout the day.
The best thing you can do is ignore how many calories you're burning during exercise because of how varied fitness trackers are. Plus, there’s no workout plan, training split, or type of exercise that is necessarily superior to anything else in terms of caloric expenditure.
More importantly to note, exercise activity only accounts for 5% of your TDEE (total daily energy expenditure) or the total number of “calories burned” each day. Again, there are SO many other ways your body uses energy or “burns calories.” Meaning, that it’s important to focus on all the other factors involved if you’re trying to achieve specific goals along with exercise. Factors like the amount of non-exercise activity (walking, fidgeting, cleaning around the house, standing, etc.) we perform daily & our food quality (i.e. how much protein we’re consuming, how much food overall we’re consuming, if we’re getting in a sufficient amount of fibrous veggies & fruit) generally have more of an impact on how much energy we “burn” daily than the hour or so we spend at the gym.
So instead of doing an exercise that your watch says you “burn” more calories performing or feeling like you have to exercise to earn your food, move it a way that feels best to you!
Because working out & eating foods that make you feel good are not meant to be a form of punishment. They’re not meant to come out of malice towards yourself & your body.
Working out & eating nourishing foods are meant to be enjoyable. Taking care of your body in this way should be an act of self-love, not hate.
And if you need some assistance re-writing this narrative within yourself, Clar-e-ty has an expert team of coaches that can help you do so. You can apply for a consultation call via the link below so we can chat all about you, your goals, & where you want to go.
Shcherbina A, Mattsson CM, Waggott D, Salisbury H, Christle JW, Hastie T, Wheeler MT, Ashley EA. Accuracy in Wrist-Worn, Sensor-Based Measurements of Heart Rate and Energy Expenditure in a Diverse Cohort. J Pers Med. 2017 May 24;7(2):3. doi: 10.3390/jpm7020003. PMID: 28538708; PMCID: PMC5491979.
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