Accuracy of Wearable - TDEE

Hi everyone,

Question about using a Fitbit or other wearable to evaluate TDEE - is it possible that over time your wearable will overestimate TDEE as your body acclimates to exercise and becomes more efficient? If so, how do you think the confidence level of the data changes over time? I ask because I find that I now have to keep a regular 500-700 calorie deficit just to maintain my weight which seems unusual when last year, following the same process, I lost 40 lbs with only a slightly greater caloric deficit (700-1000 deficit).

Just in case any of this information helps:
- In maintenance mode since November
- Training for a marathon
- Monitor my macros at roughly 40/25/35
- Looking to understand the data to prepare to recomp after the marathon

Thanks in advance for any thoughts!

Replies

  • NorthCascades
    NorthCascades Posts: 10,970 Member
    It depends on a number of things, not least the specific device you're talking about because they all have different programming.

    I guess I'm fortunate that most of the exercise I do most of the year is on a bike, so I use a power meter to measure my energy use, and am never off by more than 5%. My watch just picks the data up and turns kJs into kCals. They don't have direct force power meters for running yet sot hat's not an option for you. But, there's a lot of newer technology that measures running economy and I bet it works drastically better than a fitbit for estimating calorie use when running. Knowing your age is really a lot less useful than knowing your vertical oscillation.
  • TimothyFish
    TimothyFish Posts: 4,925 Member
    Yes, it is possible. Studies show that well conditioned athletes burn calories more efficiently while doing the same activity. Essentially, the more you train at something the better you become and the less effort it requires. Some of these devices ask in the setup whether you are a life long athlete or not. But while that might shave a few calories off the reading, there's no way for the device to know just how much more efficient you are at the activity.
  • jjpptt2
    jjpptt2 Posts: 5,650 Member
    In my opinion...

    This is one of those things that is certainly possible, and conceptually it makes a lot of sense. But bigger picture, there is a far greater chance that something(s) else is accounting for that 500-700 calorie difference in maintenance. With sooo much of this being based on estimates and assumptions, there is a lot of room for error.

    For me, things are working well and I'm confident in what I'm doing when my expected results/progress line up closely with my actual. Now, that could very well mean my estimating is way off... but it's off in such a way that the errors made on the CI side match those made on the CO side. If you're making a reasonable effort to log/track reasonably accurately, then, IMO, this is about as accurate, reliable, and confident as you can get given the process.
  • Sumiblue
    Sumiblue Posts: 1,597 Member
    I have a Fitbit Flex. On days I don't log exercise it gives me a Tdee of 1700-1800 calories & I do seem to maintain on that.
  • jeepinshawn
    jeepinshawn Posts: 642 Member
    I wore a fitbit charge for awhile, then I got one with the HR, both gave me a TDEE that ended up gaining weight when I went by it. I never could get a fitbit charge to last longer then 6 months so after the last one broke I bought a Garmin vivofit HR, the TDEE it gives is an avg of 500 calories or so less then the fitbit gave. So Im hoping the TDEE is more accurate.
  • TimothyFish
    TimothyFish Posts: 4,925 Member
    I wore a fitbit charge for awhile, then I got one with the HR, both gave me a TDEE that ended up gaining weight when I went by it. I never could get a fitbit charge to last longer then 6 months so after the last one broke I bought a Garmin vivofit HR, the TDEE it gives is an avg of 500 calories or so less then the fitbit gave. So Im hoping the TDEE is more accurate.

    I saw a report from a test done on several such devices all worn by the same people at the same time. None of them were accurate, but all were consistent in the way they were inaccurate. In any case, the FitBit was one of the ones that overestimated calorie burn and the Garmin was one that underestimated calorie burn.

    The people who were offering commentary on the results suggested that these devices shouldn't be relied on for getting an accurate calorie count, but they should work fine for relative activity levels comparing one day to the next.
  • Rusty740
    Rusty740 Posts: 749 Member
    I wore a fitbit charge for awhile, then I got one with the HR, both gave me a TDEE that ended up gaining weight when I went by it. I never could get a fitbit charge to last longer then 6 months so after the last one broke I bought a Garmin vivofit HR, the TDEE it gives is an avg of 500 calories or so less then the fitbit gave. So Im hoping the TDEE is more accurate.

    I saw a report from a test done on several such devices all worn by the same people at the same time. None of them were accurate, but all were consistent in the way they were inaccurate. In any case, the FitBit was one of the ones that overestimated calorie burn and the Garmin was one that underestimated calorie burn.

    The people who were offering commentary on the results suggested that these devices shouldn't be relied on for getting an accurate calorie count, but they should work fine for relative activity levels comparing one day to the next.

    I can confirm this. I have a Garmin Vivosmart HR. Have been tracking and comparing my TDEE vs calories in since Aug 6 and predicting my weight loss vs actual loss. It's less than a pound off my weekly average (I've lost 13.5 lbs, predicted 13.8 lbs), so it's pretty good, but I still wouldn't use it just by itself and eat whatever it told me, besides, you don't know until midnight what your TDEE was for that day anyhow.