Your FitBit is making you fat

Heart disease, high blood pressure, depression, and diabetes, are just a few of the many health risks associated with being overweight; which means that more than two thirds of the US population is at risk. For most folks the solution isn’t rocket science – eat less, move more, lose weight – but that can be more challenging and nuanced than it sounds.

Knowing what we need to restrict our calories to and how many calories we burn during exercise can be difficult to determine. To answer this question, more and more athletes are reaching for wearable technology and online metabolic rate calculators, but how accurate are these new gadgets? New research published this week has found that most wearable fitness trackers are not reliable, and can in fact be significantly over or likely underestimating your energy output.

This new research tested twelve wearable calorie counting fitness trackers against a metabolic chamber (This indirect calorimetry test is a more elaborate version of the CardioCoach mixing chamber we use at Northwest Fitness for metabolic rate testing) and doubly labeled water method. Both tests are considered the gold standard for research level analyzation of energy expenditures. This testing included several top selling brands that you may be familiar with or even own; Jawbone Up24, FitBit Flex, Misfit Shine, Garmin VIvofit, Omron CaloriScan, and others. Four other devices tested are less known and have previously been validated for use in research. Surprisingly, none were found to be accurate.

During the first test, study participants wore all devices while spending 24 hours sealed in a metabolic chamber where they performed typical daily activities such as desk work, house chores, walking on a treadmill, eating, etc. The amount of oxygen consumed and carbon dioxide exhaled is measured and that number is used to determine your metabolic rate.

Following the chamber study participants were dosed with doubly labeled water (water with hydrogen and oxygen isotopes that can be identified as they are excreted) and were instructed to collect eight urine samples over 15 days while going about their normal life. During this time they were also wearing the fitness tracker devices.

The results are in and they are not looking good. While the fitness trackers were able to measure energy expenditure differences between individual people, they broadly deviated from the gold standard tests. The wearable devices overestimated calories burned by as much as 204 kcal/d and underestimated as much as 590 kcal/d.

Both over and under estimations can have a huge negative effect on people relying on their fitness tracker to help maintain a healthy lifestyle. The overestimation can give a false idea of caloric burn, encouraging athletes to increase calorie consumption beyond their activity, eventually leading to weight gain. Contrarily, underestimations can put those with underlying health conditions at risk, or deprive athletes of the proper caloric intake to properly recover.

In short, fitness trackers should not be used to make any health decisions and can’t even be used to accurately track your activity from day to day. Instead, establishing a professionally tested resting metabolic rate by indirect calorimeter is the best way to start, then using that information establish a heart rate training program derived from VO2 Max efficiency. As complicated and “sciencey” as that all sounds, both tests can be performed at any reputable performance facility, and only require about 1hr (VO2 max testing can be done to determine how many calories you are burning at different heart rate levels). Armed with this information you will be more successful over the course of your journey to a healthier life.

Look here to find the original study - Accuracy of Wearable Devices for Estimating Total Energy Expenditure: Comparison With Metabolic Chamber and Doubly Labeled Water Method - Haruka Murakami, PhD1; Ryoko Kawakami, PhD2; Satoshi Nakae, MSc1; Yoshio Nakata, PhD3; Kazuko Ishikawa-Takata, PhD1; Shigeho Tanaka, PhD1; Motohiko Miyachi, PhD1 JAMA Intern Med. Published online March 21, 2016.