Smart Watches Don’t Estimate Calories As Accurately As You Think

Using smart watches to count calories burned has become a popular trend since the middle of the last decade.  Despite its popularity, is it accurate?

Wall Street Journal recently published an interesting anecdote about a smart watch wearer who rode a rollercoaster, only to have his wrist worn robot servant alert authorities that he had just been in a car accident.  Read the full story here.

While this is a humorous example of when smart watches get things wrong, it should also serve as a reminder that your smart watch isn’t as smart as you think it is.

How Do Smart Watches Get It Wrong?

Smart watches estimate the amount of calories you burn during the day by taking your personal data (height, weight, age, gender) and entering it into a baseline calculation to estimate your metabolic rate.  While this may serve as a decent estimate, it is not completely accurate.

During exercise, your watch will utilize heart rate and time to calculate an estimate of the amount of calories you “burn” during exercise.  Keep in mind that the running apps and online calculators use the same basic formulas to estimate calories burned during exercise too.  While these math equations provide an estimate of energy utilized, they are just that, an estimate.  Your body is not a math equation.

So, How Inaccurate Are Smart Watches?

While researching to write this quick article I found myself reading through a lot of Reddit forums and other online chats.  I was alarmed to see how many people were saying the exact same things.  They all wanted to know why they weren’t losing weight despite eating less calories each day than their smart watches said they were burning.  A typical quote would read: “My watch says I’m burning 4,000 calories per day, and I’m only eating 2,000 calories a day but I’m not losing any weight!”

This is a common fallacy.

First, your smart watch is over estimating the amount of calories you are burning by as much as 30%100%.  

The two hyperlinks provided above will take you to two different studies that looked at the measurement inaccuracy.  The part that alarms me is that many people utilize these calorie estimates to determine how much to exercise and how much to eat.  This is a dangerous narrative and means for weight loss.  To learn more about this, attend our BWCLP classes coming up on October 15 and October 22.

Why Are These Measurements So Inaccurate?

To put it simply, your body is not a math equation.  Your metabolism is incredibly complex and will ADAPT to whatever you are doing for long periods of time.  We go into depth about this concept in the article linked here.  To sum it up, your metabolism favors conserving energy for important functions such as the function of your brain, heart, digestive organs, reproductive function, and immune function.  Eating very little food and trying to exercise the calories off creates a large energy deficiency.  This deficiency is seen by your body as a “stress.”  Since your metabolism favors the ability to provide energy for important functions we mentioned above, it will DECREASE your energy expenditure while at rest and sleeping by as much as 25% in order to keep the important organs functioning.  This concept is known as the constrained energy model.  And while it is still known as just a model, it is gaining a lot of traction in the scientific realm.  Here are a couple related articles here and here.

Next, these watches generally don’t take into account body composition.  If you take two people of equal bodyweight but one person is comprised of 10% body fat and the other is comprised of 35% body fat, the person with more muscle mass will burn more calories both at rest and while exercising.  Smart watches may attempt to equate this into their calculations, but generally it is also very inaccurate.

What Do We Do About This?

First, understand that for the sake of brevity we have greatly oversimplified this.  This topic alone would account for a 12 hour weekend seminar to cover all the nuance involved.  We know people don’t have the time to read a novel each week, so we shortened it up.

However, we do know you tend to have a few free hours on the weekend.  October 15 and October 22 at 9 AM we will be covering these topics in much greater depth in our BWCLP workshops.  We have room available in both classes so be sure to contact the front desk and get signed up today.

The main takeaway from this article should be to stop relying on smart watches, diet and fitness apps, and online calculator estimates of calories burned.  They are almost always grossly over estimating calories and they create very unhealthy habits and attitudes towards weight loss and health.