Body fat percentage links to bigger smartwatch calorie-estimation errors
A Florida International University study tested four popular smartwatches (Apple Watch Series 8, Garmin Forerunner 955, Samsung Galaxy Watch5, Fitbit Sense 2) against a metabolic analyzer during controlled cycling with 58 adults and found substantial calorie-estimation errors across all devices, increasing with higher body fat percentage (often 50–100% or more). Apple had the smallest systematic bias; Garmin and Samsung overestimated more; Fitbit produced several implausible readings. Skin tone did not significantly affect error. Practical takeaway: treat calorie counts as estimates and rely on trends, heart rate, and other metrics, as wearable accuracy is influenced by body composition and may improve over time.
