BIG Nutrition: Calorie Expenditure Accuracy of Fitness Trackers


BIG Nutrition: Calorie Expenditure Accuracy of Fitness Trackers

fitnesstracker-dlSeems like a lot of people are wearing fitness trackers these days. Add into the mix the number of apps that will track steps, mileage, and more on a phone, and you have a lot of data, but do you really have reliable information especially when it comes to calories burned?

Calorie Expenditure Accuracy

Men’s Health Magazine reported the results of a study published in the Journal of the American Medical Association (JAMA) in May. The researchers used a rigorous process to track nineteen (19) subjects over fifteen (15) days and compared the calorie expenditure results to those obtained from a metabolic chamber and doubly labeled water (both measure energy expenditure). They found that for trends in calorie expenditure, fitness trackers are suitable, but not valid for research purposes because they under- and over-estimate calories burned.

(Photo credit: Dana Lehman)

Shape Magazine covered the results of an Iowa State University study assessing the accuracy of fitness trackers which found less reliable energy expenditure results for 30 men and 30 women, but the assessment only included one, 60 minute workout. The researchers also noted that fitness trackers, at this time, are better at monitoring aerobic activity than resistance exercise.

Not to be left out of the game, this fall the Today Show had one reporter wear three fitness trackers and compare the results he obtained to those collected by experts at the Tisch Sport Performance Lab at the New York Hospital for Special Surgery. All three of the wearable fitness trackers overestimated the calories burned.

I wanted to share the Today Show segment, because these news segments, articles, and blogs by individuals capturing fitness tracker variability abound. While not research, there are two takeaways:

  1. I hope this keeps individuals from placing too much faith in the calorie predictions which we know little about. Trackers seem to use your age, height, weight, gender, but also probably use predictive equations based on historical research in trained men to predict the calories burned during a specific athletic activity. Wearable trackers might add heart or perspiration rate to estimate calorie expenditure. These are estimations and best guesses because the companies consider their methods for calculating calories burned as proprietary information.
  2. If you are a user of a fitness tracker, the best approach is to look for patterns in the data which may help you estimate when you are expending more energy.

Other considerations include:

  • This is a newer area of research.
  • Research studies are often small.
  • Measuring one episode of exercise is less accurate than measuring several episodes.
  • Companies are not required to test or validate that their tracker is accurate.
  • They are also reluctant to divulge how they estimate calories burned.
  • Since prediction equations use historical research that calculated calories burned by a young trained male athlete rowing 30 minutes, using that data for estimating how many calories you burn, rowing 15 minutes for example, the results may not be accurate.

Fitness trackers are terrific if they help motivate people to move more. However, caution is needed when interpreting the calorie expenditure data.

Happy and healthful eating,

Donna G. Pertel, MEd, RD, LDN


Questions about eating during the holidays? Contact me at [email protected]