Mfp calories vs Fitbit calories

Mslmesq

I'm just curious. Both mfp and Fitbit are set to lose a pound a week. And they sync so they both have my food data and fitness data. But mfp almost always tells me I'm under my goal by a little and Fitbit almost always tells me I went over my calorie goal.

I don't care that much cause I'm losing weight. So I trust mfp and am going with that. But I'm really curious as to how or why they would be so different. Anyone know?

heybales

A minor difference is the fact Fitbit uses a BMR close to but not exactly Mifflin.
They don't state what they use now.

The major difference is the end of day estimate for total calorie burn.

MFP estimates per minute burn from the time of last sync to the end of day, based on your selected Activity Level.
Most pick Sedentary (which is BMRx1.25) because MFP will correct itself with Fitbit data anyway, and to minimize end of day effect.
Since Fitbit only sends new calorie burn when 100 higher than last sync, that could be over 1 hr ago if sitting.

Fitbit estimates per minute burn from last device sync to account to end of day, based on 2 options.
1 - Personalized which uses historical weekday or weekend daily burns.
2 - Sedentary which is about BMR x 1.05.

Both do the same math for eating goal basically.

The only time it would match is if your Fitbit actual historical avg matches exactly the Activity level you selected on MFP.

By end of day they should match, though MFP can update next day after first Fitbit sync.

Mslmesq

Well that makes sense theoretically. But even the next day it looks odd.

Take Tuesday for example. Mfp is set for 1200 calories at sedentary. It gave me an extra 464 for exercise. I ate 1522 calories and it told me I was under by 142 calories. So good job right?

But Fitbit says 1522 in and 1850 out. You are 172 calories over for the day. And has an arrow in the red.

They are both set at a pound a week with a 500 calorie deficit. But obviously mfp thinks I burned 2164 calories that day to meet a 500 calorie deficit. Whereas Fitbit thinks I only burned 1850. That's a 314 calorie difference between the two. Daily, that could make a huge difference.

So, it's confusing.

heybales

Mslmesq wrote: »

Well that makes sense theoretically. But even the next day it looks odd.

Take Tuesday for example. Mfp is set for 1200 calories at sedentary. It gave me an extra 464 for exercise. I ate 1522 calories and it told me I was under by 142 calories. So good job right?

But Fitbit says 1522 in and 1850 out. You are 172 calories over for the day. And has an arrow in the red.

They are both set at a pound a week with a 500 calorie deficit. But obviously mfp thinks I burned 2164 calories that day to meet a 500 calorie deficit. Whereas Fitbit thinks I only burned 1850. That's a 314 calorie difference between the two. Daily, that could make a huge difference.

So, it's confusing.

Actually - your eating goal is set to 1200 at sedentary. And that's minimum. You probably didn't get the 500 deficit on MFP.

None of the math starts with your eating goal, it's starts with daily burn estimate, the difference is added to your eating goal.

Good job trying to eat more since you obviously did more than sedentary.

So if Fitbit said 1850, and that is 464 more than MFP's estimate at sedentary (hence the adjustment), it must be 1386 daily burn estimate on MFP.

You must be really short, and/or not much to lose.
Strong suggestion - 500 is too much deficit in that case if under 15 lbs to lose to healthy weight.
250 is more reasonable and sustainable, and will allow better workouts which will really transform the body more than mere weight loss.

So if 1386 sedentary daily burn, and 1200 minimum - you can't get a 500 cal deficit anyway on MFP.
Not even 250 for that matter.

This is a case where if a lot of that Fitbit adjustment was from just the fact of decent amount of normal daily walking, and a little exercise - set your MFP activity level to Lightly Active.

Result will be smaller Fitbit adjustments, perhaps some negatives on some low activity days. But negatives will never take eating goal below 1200 either, but notice this...

MFP will start with estimated daily burn of 1552 at Lightly Active, so 250 deficit will be at 1302 eating goal, above what it allows as minimum. 100 cal margin of lower activity before it hits minimum of 1200.

With that setting, your adjustment for a day like Tuesday would have been:
Fitbit 1850 - 1552 MFP estimated = 298 adjustment (instead of 464)

base eating goal 1302 + 298 adjustment = 1600 eating goal.

daily burn 1850 - 1600 eaten = 250 cal deficit.


Now - the only kicker to selecting Lightly Active is the end of day math as you are trying to hit goal and basically stopping eating then.

Your per hour burn that MFP would use at Lightly Active is 65 cal for estimating.
The next morning Fitbit will sync to MFP that you actually burned BMR rate of 46 cal/hr for all sitting/sleeping time before midnight since you looked.
So a difference of about 20 cal/hr.

So if you hit the couch at say 8pm and try to have your eating goal met by then - MFP was estimating final 4 hrs 80 cal more than Fitbit will report the next morning.

Easy solution - leave that much in the green for final goal. Next morning after adjustment, it'll be right on.

Just do your own math, if you start sitting at 7 pm, but eat until 9 pm to reach goal, that's 3 hr x 20 cal = 60 in the green left. Not much, but meaningful.

Mslmesq

Thank you for your thoughtful reply. You obviously know your stuff.

Yes, I’m 5’2” (on a good day - lol) and only need to lose around 10 lbs. I’m actually good with a .5 a week weight loss and originally set fitbit to that, but changed it cause it didn’t match mfp. But now I see why.

I think I’ll just leave it as is. Most days I eat 1500-1600 calories, and sometimes a little more. But I’ve steadily been losing about a half pound a week and my clothes are fitting better. So it’s working for me whatever it is.

Thanks again.