I’ve been puzzling about how the Fitbit (fitbit.com) to MyFitnessPal (myfitnesspal.com) integration works and how Fitbit determines how many calories to send to MyFitnessPal as a daily adjustment/exercise entry; enough so that I didn’t really feel like I could trust it as a mechanism for tracking my caloric levels, which is the whole reason I got the Fitbit.
Fitbit calculates your calories burned and then subtracts your calorie deficit (750/day for my current goals) to come up with your daily calorie total, which will differ day by day depending on your activity level.
MyFitnessPal calculates your daily caloric level based on your goals (which equates to a calorie deficit) and your height, weight, and age.
Here’s where I did a little guess work, though:
(I think) Fitbit then takes your current caloric burn rate and presumably estimates what it thinks your total daily caloric burn will be to come up with an estimated end-of-day calorie amount (based on the calculation above). It then applies an adjustment to MyFitnessPal that when added to your MyFitnessPal daily calorie allowance will equal the Fitbit Total Calories Burned – Calorie Deficit amount. This seems reasonable, because if I have a highly active morning and then a less-active later day, the rate at which the Fitbit adjustment increases will change, and over the week or so that I’ve had Fitbit and MyFitnessPal hooked up I’ve actually seen the Fitbit adjustment go down as the day progresses, so presumably if Fitbit misestimates your end-of-day caloric burn based on early activity it has to compensate later in the day as what it thinks your end of day burn will be.
So yesterday (2012-05-01), Fitbit told me I burned 2863 calories. subtracting my 750 calorie deficit that left me with a 2113 calorie allowance. MyFitnessPal indicated that my goal with my specs should be 1660 calories, so:
2113 – 1660 = 453 calorie adjustment from my activity level yesterday.
Fitbit actually added 452 calories worth of exercise to y MyFitnessPal profile, so pretty much right on. Part of what threw me was that I had altered my calorie goals in MyFitnessPal because I didn’t trust the way the adjustment mechanism was working so things didn’t quite add up.
Here’s a table of my results over a few days (so I can track the accuracy of my guesses over time):
|Date||Fitbit Calorie Allowance||MyFitnessPal Expectation||Difference||Fitbit Adjustment|
added a table to track the results over a couple of days t see if my guesses are valid