My Zip estimates my calorie burn too low - anyone else?

LaurenAOK

*Semi-long rant post ahead!*

So I have been using MFP on and off for a few years, and have also had the Zip for a couple of years. Due to all this tracking I have a pretty good idea of how my body works and how many calories I typically burn in a day. I stopped using my Zip for quite a while, but recently picked it back up again, and I remember why I stopped now - it estimates my burn too low!

I already had a feeling it was estimating low because I've lost weight using MFP and eating 1800 calories a day, yet my fitbit says there are plenty of days when I don't even burn that much. I know that can't be right because if I was only burning 1800 or less, then I wouldn't lose weight eating 1800! So yesterday I did some math - I looked at my fitbit and it showed that for times when I'm just sitting down, like at school, I burn about 14 calories for every 15 minute window. That means, according to my fitbit, I'd burn about 1340 calories if I just sat around all day.

I KNOW that's incorrect. Every BMR calculator I've ever used puts my BMR at 1450 or above, and we all know that you burn more than your BMR anyway, even if you just sit around, due to things like digestion, speaking, fidgeting, etc. So even if I just sat at home all day I would be burning at the very least around 1500 calories, and fitbit is estimating 1340.

I have searched everywhere for a way to fix this but haven't found it. The only thing I have done is entered my weight as 5 pounds higher than it actually is, so that gives me a few extra calories burned. I also set my deficit goal to 250 on fitbit, thinking that if I eat a 250 deficit according to them then it's probably closer to a 500 deficit. But it's still really frustrating when at the end of the day my zip says I've only burned 1700 calories when I KNOW it's more like 2000. Again, years of tracking with MFP - I know how much I burn in a normal day.

I was just wondering if anyone else had noticed this and if anyone had a solution. I think the fitbit is super cool and I want to enjoy using it, but it bothers me that it's not accurate!

heybales

All activity devices underestimate, BodyMedia being the exception trying to get it better, if the sensors work well on you.

They all assume BMR level burn for ALL non-moving time.
As you mentioned, merely being awake is RMR level.
Eating digesting/processing food burns more too.
Standing no steps burns more too.

And if the BMR based on age, weight, height is low because you have more LBM and less bodyfat% than average, then that is starting low.

Now moving time is based on steps and distance, so if stride length is off, you could be missing calories there, but that's fixable.
But all non-step based exercise is going to be underestimated too, and therefore should be manually logged.
Swimming should be obvious, as well as spinning, rowing, lifting, elliptical, ect.

The way it's corrected is by adjusting your height so at least for the non-moving time, Fitbit is using a BMR/RMR average based on you and your BF% and better BMR estimate.

My spreadsheet will do that on my profile page.
Stay on Simple Setup tab and after seeing sample stats, delete all data in yellow cells, and get your own entered. Especially bodyfat % stat from the BF calc.

Now go to the Fitbit tab, delete the sample Tested RMR stat, and there is the difference between your RMR, your Mifflin BMR which MFP and Fitbit basically uses, and your best estimate Katch BMR.

And the height to change Fitbit stat to so they are using an average of best BMR/RMR stats.

Now you have to manually correct the stride length too, since the default auto is based on gender and height.

LaurenAOK

Wow, super helpful!! Thank you so much!

BarbieAS

(Sorry, I know the OP and heybales's response are kind of old.)

Interesting....my Fitbit has always OVER-estimated my calorie burn a bit (not saying OP is wrong or anything, I just mean that's my personal experience - my body fat is on the high side so it isn't a surprise), which I know based on actual change in weight vs the deficit shown on Fitbit (the differences tend to fall in the 150-200 calories per day range, give or take a bit, and I'm pretty darn careful with my food entries so it's definitely over and above what you'd expect due to just slight logging inaccuracies). I have in the past alternated between ignoring it, then being annoyed by it, then by entering a Fitbit "correction" entry into my food diary, then getting annoyed with THAT and going back to ignoring it...rinse and repeat. I never thought to change my height. I'm going to give this a try for a month or two and see where it shakes out.

(Also, I know you've heard this before, but that's some next-level Excel work, my friend. I work in spreadsheets every day and I can appreciate the time that took. Impressive.)

heybales

It started simple, mainly as I helped others with their numbers, and grew from there. At some point I decided to do it right with range names and well written formula's and such. Which then made adding on other tabs for specific purposes rather easy.
Sadly it also proved out my coding mentality, work at it until done, which doesn't work with life in general.