Adjusting FitBit TDEE

no44s4me

A little background. I lost over 60 lbs a few years ago, using MFP and adding back deliberate exercise calories from my now-defunct Polar HRM. I bought a FitBit shortly after losing most of the weight (Mar 2015). I had a Charge HR first and now have a Blaze. During the last couple of years, I’ve established a consistent exercise schedule (Weight Training 3xWeek, 30-60 mins light cardio (walking mostly) every day) and I also have over 2 years of FitBit data (avg of 3000 TDEE, 12K Steps).

I log my exercise on FitBit, log my food in MPF, and have the two synced. I also use Trendweight.
So after weight training consistently for over 2 years, I’ve gained back about 15lbs of weight, some muscle, and some fat. I’m now ready to go after the gained fat and would like to use FitBit as an integral part of the plan.

So here are my stats:
57 year old male
HT: 71”
CW: 196
GW: 185
BF%: No idea, but my waist is up by an inch and a half, straining the size 36 pants I worked so hard to get back in to.
MPF Setting: LA with Fitbit synched, which gives me a 1920 calorie baseline, negative calories enabled.

My plan:

Keep MPF and FB synched, set deficit to 1lb (down to .5 once the pants slacken up a little bit)
Protein at .8 gram per BW, maintain strength on the bar

So, I know that meticulously logging in MPF is the wildcard to this whole plan, which I concede, I haven’t been that diligent about in the last couple of years, but I SUSPECT that my FB TDEE is about 10% high.

Long story, short question:

So all that that being said, I’m going to let everything work as planned (TW is my safety net) but if the real data proves my suspicion of my FB TDEE too generous, what would be the best approach to adjusting the numbers (either on the FB or MPF side) so that the data correlation between MFP and FB is as accurate as possible?

heybales

You can back-track calculate to arrive at a new BMR, then adjust height to cause that new BMR to be used.
Of course manually setting stride length is required now too, but really should be done for accuracy improvement anyway.

That can get you close. Since BMR is used as basis for calculating TDEE too on Fitbit, may have to fiddle a bit.

For instance my LBM is higher than must be assumed going by gender, age, weight, height, because my BMR by test and calculation by BF%, is higher than by Mifflin BMR formula Fitbit is using close to.

So if you have a great accuracy on eating and were maintaining - you have your TDEE.

Get your Mifflin BMR from MFP - Apps on website (or anyplace else that gives Mifflin BMR). It is 1736.

Fitbit average TDEE over good chunk of time at same weight (say 3000 is correct) / 1736 BMR = activity level multiplier 1.728. (that of course changes with season usually, and BMR lowers with weight loss, though 11 lbs not much)

Your better TDEE figure ( say 2700) / 1.728 activity level multiplier = 1563 BMR you want Fitbit to use.

For males:
(Desired BMR for use -5-(10*CW kg)+(5*age))/6.25 = height in cm

or

(1563 - 5 - (10 x 88.9) + (5 x 57))/6.25 = (1563 - 5 - 889 + 285)/6.25 = 152.6 cm = 60 inches

You sure you think it's 10% high?

Also - do you manually log your weight lifting since neither steps (vastly under-estimated) or HR (inflated) will be accurate calorie burn?

Perhaps tracking currently eating level before you start the loss would be good idea - give you your TDEE right on - unless the mere act of logging makes changes to what you eat.

no44s4me

Thanks for the reply. I actually downloaded one of your spreadsheets some time ago and use as my go to BMR/TDEE calculator. When I plug in my strength training, etc. on the spreadsheet my activity level shakes out to be around 1.4, which obviously my FB doesn’t agree with.

As far as manually logging my weight training? Nah…. I just hit Weights on the exercise feature on my Blaze and let it do its thing. The calorie count for an hour session is usually in the 400 calorie area, but I’m on my feet between sets. When I plug in the same numbers on ExRx, it seems to be pretty close.

To your point, I think stricter adherence to accurate logging is the most critical step to taking the 10% number from theory to useful data.