Smartwatches, including Apple Watch, are inaccurate at calorie tracking, study finds

Smartwatch Calorie Tracking Limitations

A 2024 study by the Stanford University School of Medicine indicates that smartwatches, such as the Apple Watch, are not particularly accurate in tracking calorie expenditure. While these devices have improved in other areas since their introduction, their ability to precisely measure calories burned remains a challenge.

The study involved 60 volunteers and tested devices including the Apple Watch, Fitbit Surge, Microsoft Band, and Samsung Gear S2. Researchers found that while these wearables accurately measured heart rate, their calorie expenditure readings were unreliable.

Significant Inaccuracies Reported

The Stanford study, published in the Journal of Personalized Medicine, revealed substantial inaccuracies in calorie tracking. The most accurate fitness tracker tested was off by an average of 27% compared to medical-grade electrocardiograph data. The least reliable device showed an error margin of 93%.

Dr. Euan Ashley, senior author of the paper, expressed surprise at the magnitude of these inaccuracies, stating that the energy expenditure measures were "way off the mark."

Reasons for Inaccuracy

The primary reason for the inaccuracy in calorie tracking by wearables is their inability to directly measure metabolism. Smartwatches rely on analyzing data such as heart rate measurements or distance covered to make an educated guess about calorie expenditure. This indirect method leads to significant estimation errors.

Accurate calorie tracking requires more comprehensive physiological data than what can be gathered from a wrist-worn device, making it difficult for current smartwatch technology to provide reliable energy expenditure figures.