Study: Popular Smartwatches Overstate Calorie Burn by up to 25%
New research reveals that leading fitness trackers consistently overestimate energy expenditure, potentially skewing weight loss goals.
Key points
- A study found that Apple, Garmin, Samsung, and Fitbit watches all overestimate calorie burn, with errors typically between 15% and 25%.
- The accuracy of calorie counting decreases as the user's body fat percentage increases, affecting the most common demographic for weight loss tracking.
- Researchers advise users to focus on long-term personal trends rather than treating single-session calorie counts as precise clinical measurements.
Millions of people rely on smartwatches to track their daily energy expenditure, but a new study suggests these devices are systematically misleading. Researchers at Florida International University found that popular models consistently overstate how many calories users burn during exercise. This discrepancy means many individuals may believe they are in a calorie deficit when they are actually consuming more than they burn.
Watches Overestimate Daily Energy Burn
The study tested four major brands: Apple Watch, Garmin, Samsung Galaxy Watch, and Fitbit. Participants rode recumbent bikes at various intensities while wearing the devices, which were then compared against clinical lab equipment. The results showed that all four watches produced inflated calorie counts, with errors typically ranging between 15% and 25%. In some cases, the overestimation was significantly higher, leading to a false sense of progress for users aiming to lose weight.
Jason Kostrna, the lead author of the study, emphasized that the calorie numbers provided by these devices should not be treated as precise measurements. He noted that being off by hundreds of calories each week can easily result in a calorie surplus, undermining health goals. The most accurate device in the test was the Apple Watch, while Garmin and Samsung models showed the largest margins of error in their calculations.
Body Composition Affects Accuracy
The research also identified a key variable that impacts accuracy: body fat percentage. The study found that the error in calorie counting increased as the participants' body fat levels rose. This is a significant finding because individuals with higher body fat are often the primary demographic using these tools for weight management. Consequently, those who most need accurate data may be receiving the least reliable readings.
Researchers do not yet have a definitive explanation for this correlation, but Kostrna suggests that the algorithms used to calculate burn rates may struggle to interpret physiological data from users with different body compositions. This inherent limitation means that the device's output is not a universal constant but varies based on individual physical attributes, adding a layer of complexity to personal fitness tracking.
Experts Advise Tracking Trends
Despite the inaccuracies, the researchers advise against discarding fitness trackers entirely. Kostrna suggests that users should focus on tracking their own trends over time rather than relying on absolute numbers. If the device provides motivation and helps users monitor their progress, it can still play a useful role in their routine. However, users are encouraged to prioritize how they feel physically and use the data as one of several tools for improvement, rather than the sole source of truth.
The team is now extending their research to strength training, where short, intense bursts of effort pose additional challenges for algorithms. By continuing to test these devices in diverse environments, researchers hope to refine the understanding of where current technology falls short. For now, consumers should remain cautious and interpret their smartwatch data with a critical eye.
