Is this Calorie Count Accurate?

[Hakeem7898]

Hello all, just got my Charge 3 today and have a question I'm hoping you folks can help me with.

I'm a very unfit, 43 yrs old, 1.77 m tall male, and weigh 254 pounds so as you can tell, I need to make major changes which I have started. Today I went for a half an hour walk/jog to start turning things round, the jog was at a snail's pace so I feel embarrassed even calling it that, but anyway. My Charge 3 says I burnt 501 calories - my question is, is that accurate? Obviously I know you burn more the heavier you are etc from what I've read online, but in your opinion is 500 odd calories accurate? I ask because if it is I feel quite happy with that and will be aiming to get it up to 1000 calories within the coming week.

Thanks.

[JohnnyRow]

I don't know if that is accurate, but be warned against trying to increase it so much so soon.  The goal is to start doing something and keep it up.  If you try to do too much too soon and strain something and then have to stop exercising for weeks to heal, that is no help.  I would suggest maybe even forget the jogging part; be content with walking for a while, gradually increasing distance and speed, but only gradually.

[Hakeem7898]

Thanks Johnny, I hear you about not increasing too much and will keep that in mind, will keep it at a more gradual increase.

Just wondering how accurate that reading is. Anyone else had readings like that? My heart rate is high obviously due to the level of unfitness.

[Dominique · Accepted solution]

If you want, you can do some math to double-check your Fitbit’s estimate.

First, you can use an online calculator such as this one in order to determine your calculated BMR. According to the standard equation used by this calculator, your BMR would be 2048 calories. If you divide it by 1440 (number of minutes in a day: 24 x 60), it’s 1.42 calories per minute.

Next, you can use the Compendium of Physical Activities, which gives METs for a range of activities. METs are multipliers you can use in connection with your BMR per minute and the duration of your activity. There happens to be such an activity as "jog/walk combination", with a MET of 6.0:

Using these assumptions, 30 minutes of such jog/walk combination would have you expend 1.42 x 6.0 x 30 = 256 calories, which is significantly lower than your Fitbit’s estimate.

Also remember there are 24 hours in a day, so anything you do for 0.5 hours won’t have a major impact in the grand scheme of things. What matters if your aim is to lose weight is your total energy expenditure for the day (TDEE), compared to your total dietary intake. You can check the accuracy of your Fitbit’s calorie count by wearing it for a while, logging your intake, weighing yourself and comparing the predicted change in weight to the actual change seen on the scale.

[Hakeem7898]

Thanks for that Dominique! Clarified a lot of what I was looking for, wasn't aware of detailed calculations that you could do like that, nice. I'll keep checking over the next few days/week to see how well it adjusts its estimates.

[Hakeem7898]

Hey again Dominique,

Where would my heart rate fit into this? Is it included in those different parameters you mentioned, MET etc? Do you think because I'm unfit and my heart rate shoots up even at a slight jog, as it did yesterday, that that is the reason the Fitbit was showing 500 odd calories burnt?

[Dominique]

Well, the algorithm used by Fitbit to estimate your energy expenditure (calories burned) certainly includes heart rate (on models equiped with a HR monitor) as one of the parameters, in addition to movements and their intensity, as detected by accelerometers. It would therefore make sense a very high HR would inflate calories burned, even though (OTOH) accelerometers point to a relatively slow-motion activity (light jogging), not a high-paced one (sprinting).

As you keep exercising on a regular basis, your fitness level should improve and your HR decrease (for activities performed at the same intensity). This should eventually be reflected as a lower calories burn, especially if your weight is falling at the same time.