MFP, FitBit, and calorie credits for exercise

JazzAmbassador

Hi all. I'm actually not new -- I've been using MFP in conjunction with FitBit for about five months now -- but I'm trying to understand the algorithm by which MFP converts exercise information from FitBit into calorie "credits." I just happened to notice these recent data points today, and they're making me wonder:

12/2 - FitBit: 6935 steps, 27 very active minutes; MFP: credit for 162 calories.

11/30 - FitBit: 6717 steps, 15 very active minutes; MFP: credit for 200 calories.

In both cases, steps were only taken in the course of normal walking in urban space and no other exercise of any sort was recorded; in both cases, measurement was by a FitBit Zip, so only steps were measured (no sleep, change of elevation, etc.).

So how do those numbers make sense? How do fewer steps and fewer overall active minutes result in more calorie credits? I've done a bit of Googling, but haven't found an answer. Thanks in advance for your insights.

shadow2soul

My guess is slightly different speeds. If you were moving slightly faster on 11/30, then even with less steps, your going to get a slightly higher burn.

I'm not sure exactly how fitbit determines calories. What I do know is my average 30 day burn reported by fitbit is about 200 calories under what I calculated from loss vs intake.

nickylee76

Could it have been the pace at which you were walking? Have you changed anything else on your profile such as your weight or weather you are sedentary or lightly acitve?

bennettinfinity

What's the Very Active, Fairly Active, and Lightly Active breakdown for the two days? I would suspect that even though you had fewer steps on 11/30, your average activity level was higher - meaning your had significantly fewer 'Lightly Active' steps.

On the other hand, given that all calorie burn algorithms are estimates based on assumptions, in the grand scheme of things that's not a big delta... you're better off not overthinking it.

lmann72

I've found that if I don't stay active as the day goes on, I lose the calories I've burned ( gotten credit for) that I started with. Is there a difference in time of day?

lohkin

I also wonder if it has anything to do with the food you have logged on MFP. I have seen weird allowance credits, too. But I've only been using a FitBit for a week. Maybe if the food you've eaten has higher fat content it gives you less credit? IDK

Idothin

I was going to say stairs, but perhaps level of activity.

JazzAmbassador

Interesting answers, all! Per your responses, some further data:

First, I actually ingested more calories on the 30th, and stayed active longer and later that day, so those factors don't seem to apply (except in one possible way I'll mention below).

However, it does look like, while I had no very intense periods on either day, I had five moderately-intense 15-minute periods on the 30th versus 4 such periods on the 2nd. That could be a factor.

Also, my "FitBit Day" (i.e., time from when I put it on to when I took it off) was only 11 hours and 15 minutes on the 30th, versus 15 hours and 15 minutes on the 2nd -- so, for example, steps divided by active hours would yield a higher number on the 30th than on the 2nd. I wonder if that's it.

JazzAmbassador

johngroch wrote: »

Interesting answers, all! Per your responses, some further data:

First, I actually ingested more calories on the 30th, and stayed active longer and later that day, so those factors don't seem to apply (except in one possible way I'll mention below).

Oops! Meant to say I ingested more calories on the 30th, stayed active longer and later on the 2nd.

Sued0nim

lmann72 wrote: »

I've found that if I don't stay active as the day goes on, I lose the calories I've burned ( gotten credit for) that I started with. Is there a difference in time of day?

it extrapolates your burn to the end of the day - so everytime you synch it adjusts based on previous activity

jgnatca

I don't think fitbit takes in to account the calories you've consumed at all. I am pretty sure it is all based on number of steps and activity level (slow, moderate, active).

kickinmom

My Jawbone sometimes sends calories over and sometimes not. I know the question was about FitBit but it seems sometimes the interaction between MFP and other devices is not sure.

AnitaCRice

I'm not sure exactly how it works, but I've noticed some weirdness before with mine. A lot of times, mine will show more calories burned on a weekend day when I'm working around the house, cleaning, etc., than when I actually work out on a weekday. The weekday will show 25 highly active minutes, and my weekend day will have maybe 5.

The only thing I can figure out is I'm on my feet and my body is moving more consistently while cleaning on the weekend. During the week, I will workout in the morning but then be sitting a big part of the day at my desk at work.

GothyFaery

I had a similar problem when I first got mine. For me it actually gave me more calories when I forgot to wear it and literally got 0 steps than when I was wearing it. Turns out Fitbit will assume you burn calories if you get a lower step count. You can turn that setting off so Fitbit will only count the calories it records.

On the Fitbit site, go to settings, Personal Info, Preferences, Calorie estimation, set to disabled.

Not sure that's your issue but it might be worth checking out.