Adjusting MBR

Kitzi7

Hi! I read threw pretty much everything but couldn't find an answer to my specific problem.

I know fitbit calculates my BMR by using age (22), height (5 foot, 9.3 inch), weight (167,5lbs) and gender (m).

But it doesn't take into account how much muscle mass/body fat I have. Since I do weight training 5 to 6 times a week I have higher muscle mass than average. My body fat percentage is at 8.

Fitbit gives me a BMR of 1755 calories and from an accurate lab test (which takes muscle mass into account) I know that I am at 1900 BMR (150 calories off!). But I can't change my BMR manually. Now I found out that Fitbit also uses a formula based on your BMR when you do activities.

Where is the point of tracking for me if everything is wrong?
I am totally frustrated. Hope someone can help me.


Does it make sense to lets say go on "decent active" on MFP and manually increase the calories it comes up with by 150?

editorgrrl

You're overthinking this. Use Fitbit as intended for several weeks, then reevaluate your progress.

heybales

I think you are very correct to want to get it improved if you can.

Because isn't that the whole purpose of using the device in the first place - improved accuracy potential?

And yes - you can indeed improve it more.

So with your stats.
Katch BMR using 8% BF = 1880
Cunningham RMR using 8% BF = 2038

Your tested RMR = 1900

They don't test your BMR actually, they tested your RMR, which higher than BMR. Look at your stat sheet given at test time.

Anyway, unless effected by diet, tested RMR is usually within 5% of calculated based on BF% that was measured accurately.
What this means is either your BF% estimate is actually a tad more than you think (like 16%), or your metabolism is slower than it needs to be based on LBM, by about 138 calories.

Then again, maybe the 1900 is rounded off too much.

Did you get the RMR test after having been in a diet for awhile?

Anyway, change your height stat on Fitbit to 73.5 inches, and it will start using a BMR figure that is average of your Katch BMR and measured RMR.

You will have to manually check your stride length walking and running, check the FAQ on how to do this well.
Because the default uses your gender and height to calculate stride length, and that is incorrect now.

This info was obtained from the spreadsheet on my profile page.
Simple Setup tab, and Fitbit tab.

Kitzi7

First of all: THANK YOU SO MUCH for your help. I really appreciate it.

I attached my test I did 2 weeks ago - I already did a couple before that which show similar results. The Inbody 720 was used and as far as I researched the numbers should be pretty accurate.
Sorry that the test is in German (I live in Austria) but I circled my body fat percentage and where it says "BMR 1897kcal". It's always said that weight training increases your BMR, but fitbit doens't take that into account - makes me a little sad

I also attached a random picture of myself I just took so you can make an opinion on whether my percentage could be correct. 16% would definitely be too high I think.

The third image is a screenshot on the calories fitbit calculated for me before I wore my charge HR. It is at 1755kcal - I guess that's the BMR fitbit uses for me. (I have no idea which formula it is).

Anyway, I just increase my height now until he puts me to 1897 BMR (+142kcal) and change my walking and running stride length?

Thank you heybales!

Kitzi7

I changed my height in the Fitbit settings from 176cm (=69,3 inch) to 196cm (=77,17 inch) now.
Am I correct that I have to change it in MFP too? Do both applications use the same Mifflin BMR formula?

heybales

They do, but MFP is always going to correct itself to what Fitbit reports - so not needed on MFP.
Though it would cut down on the size of the adjustments if that makes planning the eating day harder.

Also - you did not have an RMR test done actually.
You had a bodyfat test done as you know, and just like I did, they ran a calc using that to come up with estimated BMR figure.
They must have used something other than Katch, I think Nelson BMR calc. (yep, there's a bunch of calc's for BMR and RMR).
RMR test would be you sitting breathing in to tube for about 20 min.

So I'm going to change my recommendation based on that, since the BF% was tested, and based on calculated BMR and RMR.

Height is now 82.1 inches or 208.5 cm.

Congrats! You are sprouting like a kid, several inches in 1 day.


After you make that change, go look at your Fitbit daily graph per 5 min blocks. Find your sleeping/non-moving time calorie burn for a 5 min block. Divide by 5 x 1440 = BMR they are using.

Should be about 1956.

Kitzi7

Thank you so much for all your advice!
You really are an expert on this stuff!
Before I asked here I tried my luck on the German Fitbit page and one of the hosts told me that there is no way to change it.

But why do you recommend me to go at BMR=1956? Isn't that too much?
Shouldn't be 1880 - 1900 BMR be enough? With a height of 196cm (or 69,3 inch) the Mifflin - St. Jeor equation puts me to 1880kcal.
And fitbit puts me while sleeping on 6,5 calories for a 5 min block.
6,5/5*1440 = 1872 kcal BMR

Did I miss something or did I calculate wrong?

heybales

Fitbit uses an undisclosed BMR formula that is close to Mifflin, but not exactly the same.

The reason why I use an average of BMR and RMR calculated on BF%, is because Fitbit actually underestimates daily burn.

It assigns BMR level burn to all non-moving time, but it should only be sleeping time.
Awake sitting is RMR level, which is higher.
Standing is even more.
Processing/digesting food is even more, about 10% of calories eaten.
All that is unaccounted for and given BMR level burn.

If you get your sleeping in for 8 hrs, that is 1/3 of the day.
Average person has at minimum another 1/3 of day not moving much, so that should be RMR level burn.
That leaves the other 1/3 to be based on either steps/distance or HR based calorie burn.

So an average of BMR/RMR is used for about 2/3 of your day, that should be close to a 50/50 split.
You may vary, it's not a huge amount of difference after all, but since doing the math on better BMR anyway and getting height adjustment needed, I figured why not get a tad more accurate if possible.

cindytw

SO if you have 8% BF, you do NOT need to worry about what Fitbit says! Seriously, you are over-thinking and over-analyzing! You are FINE!!

flamingblades

I got a fitbit flex, and all I can seem to do with it is track my sleeping patterns and my walks. Sometimes it won't track my sleep. I sync the #*&^ thing first and it still only works about 1/2 the time. I have searched for more info on it because the little booklet that came with it doesn't tell you diddly. Any advise on how & where to find info on my Fitbit and how to use it would be greatly appreciated.

retirehappy

flamingblades wrote: »

I got a fitbit flex, and all I can seem to do with it is track my sleeping patterns and my walks. Sometimes it won't track my sleep. I sync the #*&^ thing first and it still only works about 1/2 the time. I have searched for more info on it because the little booklet that came with it doesn't tell you diddly. Any advise on how & where to find info on my Fitbit and how to use it would be greatly appreciated.

Some units can be defective maybe yours is, check with their CS dept. if the forums and guide don't resolve the issue.
Flex help forum
https://community.fitbit.com/t5/Flex/bd-p/flex
or Fitbit's customer service
http://help.fitbit.com/?p=flex
link to email them is at the bottom of that page also on that page is Flex 101 how to guide.

heybales

cindytw wrote: »

SO if you have 8% BF, you do NOT need to worry about what Fitbit says! Seriously, you are over-thinking and over-analyzing! You are FINE!!

Actually, for maximum performance gains, eating at the right level is so important, as too much deficit when cutting can take awhile to show up in performance degrading.

So actually at this level is when accuracy is even more important for amount to eat.

Just like when you have a lot to lose, almost any deficit and exercise will show improvements.
That is not the case when you get down to having less to lose, then accuracy of say what you eat is even more important.

As in this case, with BMR being 150 off may not seem like much, but since it's used to estimate calorie burn for all movement, that difference can easily become 300 for daily burn.

If you are intending to keep a small deficit - that just ruined your goal.

That's exactly why I got the Zip couple years back, aid in keeping the deficit small. Just needed some tweaking for my higher measured RMR and LBM than Fitbit is expecting for average.