Your Watch Isn’t Accurate at Tracking Calories (and Cardio Isn’t Effective for Fat Loss)

A meta-analysis published in the Journal of Medical Internet Research in 2022 reviewed 65 studies and concluded that our wearable fitness trackers are wildly inaccurate at measuring calorie expenditure (the study included every major fitness brand you can think of).

Bottom line: Don’t use your smartwatch to track calories burned.

More broadly, cardio workouts aren’t effective for burning calories and losing body fat.

People who burned 800–1000 calories per week from their cardio lost just 1.1 pounds over a 6-month period. Doubling this amount of aerobic exercise showed only a modest increase in weight loss.

Why don’t we lose weight when we do cardio? Two reasons:

1. We eat more.
   We tend to reward ourselves after doing cardio, and the hormone that regulates hunger is upregulated after aerobic training. So hunger is a normal physiological response to cardiovascular exercise.

2. Our energy expenditure throughout the day drops.
   Our Energy Expenditure due to Physical Activity (EEPA)—the number of calories we burn when we aren’t exercising—decreases after we do cardio. Our body subconsciously finds ways to conserve energy (we fidget less, for example).

Take-home message: Perform cardio for heart health, not for fat loss. Stated otherwise: cardio doesn’t do what almost all of us are using it for.