Wonder why you aren't losing weight? Your smartwatch could be lying to you - scientists warn devices don't give accurate calorie counts

Daily Mail​

2 days ago

They are relied upon by fitness fanatics to record all manner of data from their length of runs to heart rate, pace and even changes in elevation during a jog.
But one thing smartwatches shouldn't be relied upon when exercising is counting calories, scientists claim.
Academics said the devices are not accurate at working out how many units of energy have been lost during exercise.
In fact, researcher Dr Cailbhe Doherty claimed there is a 'high degree of error' in the methods used.
This means that watches may tell users they have burnt 1,000 calories - when they have actually only burnt 300.
The UK accounted for 4.4 per cent of the global smartwatch market in 2022, according to data from business consultancy Grand View Research, and is projected to lead the European market in terms of revenue in 2030.
But, Dr Doherty said the portable wearable computers aren't all bad - and are accurate at measuring heart rates and GPS.
The academic, who investigates the accuracy of wearable consumer devices at University College Dublin, was asked on the CrowdScience podcast if smartwatches were accurate at counting calories.
Dr Doherty said that while smartwatches could accurately measure heart rate or GPS, they were not as good at recording 'energy expenditure', such as sleep patterns (file picture)
In response, the lecturer and assistant professor at the university's School of Public Health, Physiotherapy and Sport Science, said: 'The evidence would suggest that they're not.
'And that's likely because the way they estimate, the way most smartwatches would estimate calories, is using accelerometry by itself, or accelerometry and photoplethysmography.
'So measuring heart rate and some variation of physical activity through movement.
'Now that's very different to actually measuring someone's inspired and expired gas, which is what you would use to measure calories in the first place.
'Essentially, the signal is so far removed from the original biometric rhythm that there's such a high degree of error that can be introduced that way.'
Smartwatches measure your heart rate and step count and use that to come up with a guess of how many calories have been burn.
This estimate can depend on different assumptions made by the algorithm of the device.
Dr Doherty said a recent systematic review of smartwatches found that the margin of error can be between 30 per cent and 150 per cent.
As an example, he agreed that a watch may tell users that the burnt 1,000 calories when they have only burnt 300.
The academic continued: 'When it comes to something like heart rate or GPS, yeah, accuracy can be really good.
'But energy expenditure, the number of calories you burn, your sleep, smartwatches aren't as good at that stuff.
'If you think about the number of signals that a smartwatch has to measure to measure sleep, any error in those individual signals, any error in your heart rate, your respiratory rate, the amount you're moving, all of those compound up.
'That's probably why smartwatches aren't as good at measuring your sleep, because the separation from the original signal being sleep and the output, your sleep score, the time you spend sleeping, it's much larger.'
Walking 10,000 steps a day has traditionally been seen as the holy grail in order to stay fit and healthy. But a study led by the University of Granada reported in 2023 that the number has 'no scientific basis'.
This research instead concludes that 8,000 was 'the optimal number of (daily) steps at which most people obtain the greatest benefits', and suggested that walking faster could provide additional health benefits.
According to Grand View Research, the US-based market research and business consultancy, the UK smartwatch market generated a revenue of £1.24bn in 2022 and is expected to reach £2.16bn by 2030, with the market expected to grow annually by 7.2 per cent.