You might not be as active or as fit as your fitness wearable device is telling you. According to a new scientific study, many such leading wearables are inaccurately reporting the amount of calories burned each day compared to traditional calorie counting methods,

As reported by Mobi Health News, JAMA Internal Medicine published a scientific paper yesterday authored by Japanese researchers from Tokyo’s National Institute of Health and Nutrition. The researchers found many popular fitness wearables registered an error margin of about 200 calories per day when measuring energy expended.

UCSF internist Dr. Adam Schoenfeld said that this study shows FDA regulation is needed for mobile apps that are used as medical devices.

“Use of health-related apps may pose little risk in healthy persons if the information collected is not used for medical decision-making, but these apps should still undergo basic testing for accuracy,” said Schoenfeld. “For mHealth apps that are designed to play a role in medical care, documenting the validity and accuracy of measurements is crucial.”

Several type of fitness wearable tested

The researchers tracked study participants wearing either popular wearable devices or healthcare devices, and compared these readings to two other methods of measuring calories burned. The non-device calorie tracking was either through urine samples or a metabolic chamber that measured oxygen and carbon dioxide.

The consumer wearable devices measured were: Withings Pulse O2, Misfit Shine, Tanita AM-160, Omron CalorieScan HJA-403C, Jawbone UP24, Epson Pulsense PS-100, Fitbit Flex and Garmin Vivofit. The healthcare devices were: Omron Active Style Pro HJA-350IT, Panasonic Actimarker EW 4800, ActiGraph GT3X and Suzuken Lifecorder EX.

In the urine test, all devices underestimated calories burned, with a range of a small shortfall of 69 calories (Omron Active Style Pro) to a large underestimation of 590 calories (Jawbone UP24).

The metabolic chamber results were more widely varied, with both Omron wearables overestimating energy expenditure by about 200 calories while the Withings and Jawbone wearables underestimating calories burned by nearly 270 calories. All other devices registered results within that range, though the Epson and Panasonic wearables were the nearest to the standard results.

The researchers suggested that the varied results may have come from various factors, notably that study subjects could not wear the devices all the time. They added that the test subjects had healthy weight profiles, and future studies should include overweight subjects as well.

This study follows other research into wearables’ accuracy, most notably the American Council on Exercise’s study released in February that also found calorie tracking issues with commercial fitness devices.