Can you really trust your tracker? Members often share their doubts on the SparkPeople message boards. "My fitness tracker shows that I'm burning about 600 calories through daily exercise. My calorie range then increases to 1,800 to 2,150. Can I really expect to lose weight by eating that many calories?" one member pondered.
As a registered dietitian, my typical response for years has been this: Be careful with "eating back" all those calories you burn through exercise based on your fitness tracker. Honestly, I'm with the many skeptical members, having never really trusted the calories burned report on trackers, and guess what? We were right—these fitness gadgets are no good at accurately reporting the calories you burn.
The Research
A recent research study conducted by the Stanford University School of Medicine evaluated the accuracy of wrist-worn activity trackers in reporting energy expenditure, commonly referred to as calories burned. The study, published in the Journal of Personalized Medicine, evaluated the Apple Watch, Basis Peak, Fitbit Surge, Microsoft Band, Mio Alpha 2, PulseOn, and Samsung Gear S2. These devices were strapped to 60 volunteers (29 men and 31 women) who underwent a range of activities, such as sitting, walking, running and cycling. At the same time, the participants were being assessed using an indirect calorimetry machine that calculated actual metabolism by measuring oxygen and carbon dioxide in the participants' breath. Then, the data from the tracker was compared to the data from the indirect calorimetry machine.
The results showed that these fitness trackers basically "flunked" when it came to measuring how many calories a person burns through activity and exercise. None of the seven devices measured energy expenditure accurately. That's right—none of them. The inaccuracy ranged from 27 to 93 percent, which means that the worst performing device was wrong a whopping 93 percent of the time and even the best performing device was still inaccurate 27 percent.
Another interesting finding from this study was that there was even "greater error" in people with darker skin, tattoos, higher BMIs and men; the error was slightly less for Caucasian women and those with a healthier BMI, which is an issue since most SparkPeople members set a weight-loss goal due to their higher BMI. Therefore, relying on the calories burned information from a fitness tracker could be greatly impacting one's weight-loss effort.
Adjusting Your SparkPeople Program for Improved Accuracy
Until fitness trackers can accurately measure energy expenditure, you may want to do some investigation and make adjustments to your SparkPeople program. Realize that the program used at SparkPeople to determine your calorie range already calculates the calories you burn at a resting state (metabolism) and uses the lifestyle activity factor (sedentary, lightly active or active) that you selected when you joined the site. This activity factor accounts for your movement throughout the day outside of exercise, including as daily chores and your job. If needed, you can adjust that setting here.
There are two different ways to account for your planned exercise in your program setup: The first is to connect your fitness and nutrition trackers so that when you track exercise, your recommended calorie range changes accordingly. The second is to disconnect communication between your fitness and nutrition tracker, so your calorie range is based on a calories-burned goal and does not fluctuate depending on the activity you track. Regardless of which method you use, it's important to be sure your activity tracker is not overstating your calories burned, resulting in a calorie range that's too high to help you reach your weight-loss goals.
An easy way to check the calories burned through your planned exercise versus the numbers the activity tracker is providing is by using SparkPeople's "Calories Burned List." Manually add up your exercise using this list as a reference, then compare to the results given by your activity tracker. Do this for a week or so to get a good idea of how close those numbers are to one another.
After those days pass, evaluate your results. If you discover that your activity tracker and your manual calculations are similar, then leave your program as is. If, however, you notice a discrepancy between these two values, then you may want to change the method that you use to determine your calorie range within the SparkPeople program. If the latter is true, you have one of two options, the first of which assumes you will disconnect your activity tracker from your SparkPeople account and the second which assumes that your tracker will remain connected.
Option #1
If your fitness and nutrition trackers are not connected:
Disconnect your activity tracker from your SparkPeople program so that the calories you burn through planned exercise is not changing your calorie range daily. Adjust the calories burned weekly in your SparkPeople program to match what you are typically doing. Now you will have a calorie range that is a better reflection of your exercise plan.
If your fitness and nutrition trackers are connected:
Disconnect your activity tracker from your SparkPeople program and manually track your exercise daily. Your calorie range will change depending on the calories burned, but this range will be a better reflection of the exercise you're actually doing.
Option #2
If your fitness and nutrition trackers are not connected:
Keep your activity tracker connected to your SparkPeople program, but set your calories burned goal so that you're only"eating back" half the calories your activity tracker shows you are burning daily. This should be close to the amount you manually calculated during your experiment.
If your fitness and nutrition trackers are connected:
Keep your activity tracker connected to your SparkPeople program, but only opt to "eat back" half the calories you are burning daily through your planned exercise or the whole amount you manually calculated during your experiment.
Bottom Line: Before you trust the calories burned report from your activity tracker, do some experimenting and investigation to determine accuracy. Make the necessary adjustments as you prefer to ensure that your calorie range jives with those weight-loss goals you're working so hard to achieve.
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