Fitness trackers like Fitbit have become incredibly popular in recent years as a way to monitor physical activity and health metrics like steps taken, calories burned, heart rate, sleep tracking and more. Fitbit offers a wide range of activity trackers at different price points, but all of their devices provide detailed stats on calories burned. This allows users to track their energy expenditure throughout the day to help meet weight loss or fitness goals. But how accurate are Fitbit devices at measuring calories burned? And which Fitbit model is the best for tracking this important metric? This article will provide a detailed overview of how Fitbit devices estimate calorie burn and compare the features and accuracy of different Fitbit models to determine the best Fitbit to track calories burned.
How Does Fitbit Calculate Calories Burned?
All Fitbits use proprietary formulas that factor in user data like weight, height, age and sex along with metrics like heart rate, active minutes, distance traveled and steps taken to generate personalized calorie burn estimates. Here’s a quick overview of how Fitbit devices estimate calorie expenditure:
Resting Metabolic Rate
Fitbit calculates your resting metabolic rate (RMR) to determine your basal metabolic rate (BMR) – the minimum number of calories your body needs to perform essential functions at rest. It does this by taking into account your personalized stats like weight, height, age and sex. Your RMR makes up the majority of the calories you burn each day.
Heart Rate
Many Fitbit devices use purepulse heart rate monitoring technology to track your real-time heart rate throughout the day. Your heart rate data helps determine your calorie burn because the faster your heart beats, the more calories you use.
Active Minutes
Fitbits track your active minutes when your sustained elevated heart rate indicates you’ve been exercising or participating in activities more intense than just walking. Active minutes correlate closely with calorie burn.
Steps Taken
Fitbits use your number of steps taken to estimate distance traveled and the intensity of your activity. More steps generally means more calories burned.
Motion Sensors
Many Fitbits have 3-axis accelerometers that track motion patterns to detect activity and exertion levels. This motion data feeds into calorie burn calculations.
Tracked Exercises
When you log exercises like runs, swims, or strength training in the Fitbit app, it applies specific MET values (metabolic equivalents that show the intensity of activities) to more accurately calculate how many calories those workouts burned.
User Data
Personal stats like your weight, height, age and sex all help determine your total daily energy expenditure because they affect your RMR. As you log your weight over time, Fitbit periodically adjusts its calorie burn estimates.
So in summary, Fitbit devices combine your quantified self data with scientific formulas and patterns recognized by their algorithms to estimate calorie expenditure. But how accurate are these estimates in real life?
How Accurate Are Fitbit Calorie Burn Estimates?
Overall, Fitbit devices provide reasonably accurate estimates of daily calorie burn compared to more complex clinical methods like double-labeled water testing, indirect calorimetry and metabolic carts. But the accuracy can vary quite a bit based on the specific activity being performed. Here’s an overview of some independent research on the accuracy of Fitbit for tracking calories burned:
Resting Metabolic Rate
One study published in the Journal of Personalized Medicine evaluated the accuracy of five different Fitbit models for estimating resting metabolic rate compared to a metabolic cart test. On average, the Fitbits overestimated RMR by 8.1%. But results varied between models, with some as high as 12.8% over and others only 0.3% over.
Low Intensity Activities
For low intensity lifestyle activities like light walking, cleaning, etc., one study in BMC Sports Science, Medicine and Rehabilitation found Fitbit devices overestimated calorie burn by an average of 10.3%. Results varied from an overestimation of 2.8% up to 34.4% depending on the specific model.
High Intensity Exercise
Fitbits tend to be more accurate at estimating calories burned during high intensity exercise. A study in the Journal of Strength and Conditioning Research compared Fitbit calories burned to indirect calorimetry during treadmill running. On average, Fitbits overestimated calorie burn by just 2.7% compared to 13.8% and 19.5% during low and moderate intensity walking.
Strength Training
For resistance exercises like weight lifting, Fitbit typically underestimates calorie burn. One study published in the Journal of Sports Sciences found Fitbit underestimated calorie burn by about 10% compared to indirect calorimetry measurements during circuit weight training.
24-Hour Energy Expenditure
Over the course of an entire day of varied activities, Fitbit calorie burn estimates have been shown to fall within about 10-15% of measurements from gold standard doubly labeled water testing. Not perfect, but still reasonably accurate for most users.
So in summary, Fitbit tends to overestimate calorie burn for low intensity daily movement, provide relatively accurate estimates for high intensity exercise, underestimate calorie burn for strength training, and provide reasonable approximations of total daily energy expenditure. But which Fitbit model is best for tracking calories burned?
Best Fitbit for Calorie Tracking Accuracy
While all Fitbits use similar algorithms to estimate calorie burn, some models tend to provide more accurate results than others. Based on independent validation studies, here are the best Fitbit devices for tracking calories burned:
Fitbit Charge 5
The Charge 5 is Fitbit’s newest and most advanced fitness tracker. It has some of the most accurate calorie tracking according to validation studies. The Charge 5 provides the closest estimates to indirect calorimetry measurements across a wide range of activities thanks to its active zone minutes feature which closely tracks different heart rate zones.
| Pros | Cons |
|---|---|
| – Most accurate for calorie tracking | – Higher price |
| – Active zone minutes | – Limited smartwatch features |
| – EDA stress sensor |
Fitbit Sense
The Fitbit Sense is Fitbit’s most advanced smartwatch and provides similarly accurate calorie tracking to the Charge 5. It matches the Charge 5 in calorie burn accuracy in validation studies which is impressive given its more slim smartwatch design. The Sense provides overall calorie estimates within 10% of indirect calorimetry measurements.
| Pros | Cons |
|---|---|
| – Excellent calorie tracking accuracy | – More expensive |
| – Premium smartwatch features | – Shorter battery life |
| – EDA, ECG and skin temperature sensors |
Fitbit Versa 4
The newer Versa 4 smartwatch offers calorie tracking on par with more expensive Fitbits due to its inclusion of the active zone minutes feature. It provides more accurate estimates than the Versa 3 and other older Fitbit models lacking active zone minutes. The Versa 4 is the most accurate option that combines solid calorie tracking with full smartwatch capabilities at a more reasonable price point.
| Pros | Cons |
|---|---|
| – Excellent accuracy for the price | – Less premium than Sense |
| – Active zone minutes feature | – Shorter battery than basic trackers |
| – Full smartwatch functions |
So in summary, the Fitbit Charge 5 or Sense provide the absolute best accuracy, while the more affordable Versa 4 offers impressive calorie tracking for a smartwatch. But any Fitbit model utilizing heart rate data and active minutes will provide reasonably accurate estimates you can trust for calorie tracking. Pair your Fitbit with the app to log workouts and enter accurate body stats like current weight for optimal accuracy. And remember calorie estimates are not perfect – go with long-term trends rather than obsessing over day-to-day numbers.
Conclusion
Fitbit devices use your personalized metrics like age, sex, weight along with heart rate, active minutes, steps and motion data to generate calorie burn estimates that are reasonably accurate compared to clinical methods. Validation studies show Fitbit tends to overestimate at rest, underestimate strength training, but provides good accuracy during high intensity exercise. Overall, total daily calorie estimates are typically within 10-15% of doubly labeled water testing. Among Fitbit models, the Charge 5 and Sense provide the highest accuracy, while the newer Versa 4 also offers solid tracking for a smartwatch. In the end, any Fitbit utilizing heart rate and active minutes provides reasonably trustworthy estimates you can use to monitor calorie expenditure and progress towards your health and fitness goals. Just don’t obsess over the exact numbers on a daily basis.