Calorie burn accuracy

Flookbird

Hi everyone,

I'm a regular lurker but not regular poster on these boards. I've had my Fitbit Flex since the start of August and I love it! It's doing exactly what I wanted in that it is helping me to be more active the closer I am to my goal weight. I am signed up for the Premium option as I love data and love seeing myself in comparison to others as it's very motivational.

At the moment, my only non FB tracked activity is 25 mins a day of swimming breaststroke. I'm trying to increase the intensity of this gradually. I log it on MFP.

My question really revolves around the accuracy of the FB calorie burn estimate. I'm a teacher so since I've been back at school I've been doing just under 10k steps a day at work (although trying my best to take as many steps as poss/staying on my feet). I then walk the dog at home and try to get to 12k a day.

As my MFP profile is set to sedentary (I find that easier when using the FB) I'm getting pretty good adjustment calories from FB. How accurate do people find this to be? Based on my fitbit data I should be losing over 2lbs a week (although I don't want to this close to goal). But am losing around 1-1.5lbs. I think I log quite accurately (my diary is open if you want to check!).

I'm following Weight Watchers at the minute so the MFP stuff is by the by for now, but I'd be interested to know how accurate people find it to be as I think I'm going to find it increasingly useful as I move to maintenance.

Hope that all makes sense and I'd be grateful for any insights anyone has. My net calories many days are quite low but I'm sticking to WW as I know it works!

heybales

I had 39 days of training for a race, so manually logging all exercise.

My TDEE based on accurate eating records (by weight, not measurement) and amount lost was 3528 daily average.

Fitbit TDEE during that same time was 3494, so within 1% difference.

Now, I did tweak the height up on Fitbit so it was using a BMR/RMR based on bodyfat instead of the usual age, weight, height.
If I had not done that, it would have been off.


You should NOT be attempting to lose 2 lbs weekly this close to goal weight - you are just stressing out your body badly.

If really within 4 lbs of goal weight, then 250 cal deficit or 1/2 lb weekly is reasonable.

If you've been in a diet for a long time for that 70 lbs (good job), then you likely lost more muscle mass than you care to know about - meaning your metabolism is slower than age, weight, height would estimate (mine was higher).

And for that to happen - you have suppressed your body in addition to that slow down by having too great a deficit this long, and with upwards of 20-25% suppression of TDEE, you don't burn as much as your Fitbit is estimating based on an average healthy body. Your's is not as this point what it thinks it is.

So that's probably right then, losing less than it would seem you should.

But that's the problem with taking a bigger than reasonable deficit - your body will force slow weight loss on you if you don't purposely take it.

But if you want to do it - then at this point suck it up and eat even less. If you haven't reached that max 20-25% suppression, you'll keep not losing weight, until you keep eating so little or exercising so much you eventually do.

But I'm betting that level of eating with that required amount of exercise will suck, and that's where failure to adhere and keep weight off fails. And with less muscle, easier to gain it back too.
And what happens if you get sick and can't exercise that much or at all - you'll have to eat so little. What about vacation with less exercise and wanting to eat more. All that means easy fat gain.

This doesn't have to happen.
http://www.youtube.com/watch?v=2i_cmltmQ6A

itsjustmish

I keep a spreadsheet showing my calories eaten (according to MFP) and calories burned (according to Fitbit) and for the past 4 months I should've lost 13lbs based on the information I have. I've actually lost 8lbs, so that's quite a big difference. However, I have eaten in restaurants and at friends houses at least once a week on average over that period, so although I've tried my best to log as accurately as possible, in reality I have no idea how close I have been with my food entries.

It's probably down to a combination of Fitbit overestimating my burn combined with me underestimating my food intake.

Fitbit gives me an average daily burn of around 2050 per day, whereas my TDEE as calculated on the Scooby website comes out to around 1950. So, in conclusion, I have absolutely no idea whatsoever as to how accurate it is but it does definitely motivate me to move more! I do around 17,500-18,500 steps on weekdays and usually more like 25,000-30,000 on weekends in addition to Body Revolution 6 days per week and You Are Your Own Gym 3 days per week.

Flookbird

Thank you both for your really detailed replies! I really appreciate them.

I'm not trying to lose 2lbs a week now - wanting 0.5-1lb a week if possible and happy to stay the same too. I'm trying to gradually increase my intake so that I can find a good level for maintenance.

All that you've said about why daily burn estimate is probably too high makes good sense to me and settles my mind, so thanks for that. Hoping that if I continue the exercise and start eating more I'll regain some muscle and look better even if not weighing lighter?

In terms of duration - it's taken me 9 months to lose the 70lbs and I'm really keen not to regain - hence the questions/research etc. have had a holiday - drunk loads but kept up exercise and lost the 3.5lb 'gain' within a week!

heybales

Increase calories slowly then, though you should gain some water weight back with more stored carbs in muscles. Those are always depleted to some level in a diet. First big water weight drop when you start one.

Fitbit normally should underestimate for several reasons, outside what I mentioned regarding lost muscle mass fooling them.
It counts BMR level burn for ALL non-moving time, that's the burn if you are sleeping. Look at Activities tab daily burn graph.
When awake you actually burn more - RMR.
When standing non-moving you burn even more.
When processing and digesting food you burn more, about 10% of what you eat. (eat 2000, burn 200 dealing with it).

All of that extra burn is NOT accounted for, so it is underestimating your normal daily activity. The more sedentary you are, the more underestimated you are.
Exercise usually is too, unless you manually corrected stride length, and your workouts are only walking and running.

If you are doing resistance training, strength training, you can regain some muscle if eating near/at/over maintenance, depending on how long you've been doing lifting.
If you aren't lifting, eating closer to maintenance won't gain muscle, you'll just stop losing it.
But even at maintenance, or a reasonable minor deficit for amount to go, with lifting, can trade fat for muscle slowly but surely. And even though it may be 1 lb every 8 weeks if you are doing it right, 1 lb of fat in the right place being gone can look major.