![]() And, every time I log a weight, I have the option to input body fat %, and obviously if I had something like an Aria scale it would import that value automatically each time I measured it. which was 21%! Why in the world would it offer a default value that does not match the assumed value in the formula it uses? This is bonkers. I hadn't done the measurements at that time, so I accepted the default value for women that it offered me. When originally setting up my Fitbit profile, it asked my gender, age, height, weight. Here's the thing that really gets me, though. ![]() ![]() But that's super annoying, because as I continue to build muscle I'm going to have to track body fat and Katch-McArdle BMR in a separate spreadsheet in order to figure out how much to mentally increase Fitbit's estimated maintenance amount. And it matches the fact that I now have to eat 100 kcal/day OVER what Fitbit estimates, just to maintain weight. I'm now no longer surprised that I lost weight WAY faster than expected with a theoretical 250 kcal/day deficit when I originally started, because in reality it was a 350-400 kcal deficit. Jeor estimate for women assumes body fat of ~33%!! Playing around with different body fat values in the formula, it seems the Mifflin-St. I've never had a "real" body fat measurement, but using the Navy and Covert-Bailey tape measure methods my estimate is 20-25%, which is pretty average for a fit woman. Using the Katch-McArdle BMR formula which incorporates body fat percentage, my estimated BMR is 1250-1300 kcal. Using that formula, my estimated BMR is ~1150 kcal, which matches the 12 kcal/15 minutes basal expenditure that Fitbit shows for me during sleep. It seems clear from other community posts and looking at online calculators that the Fitbit software uses the Mifflin-St.Jeor formula to estimate BMR from gender, age, height, and weight. I came to the conclusion that it must be underestimating my BMR. I've been trying to figure out how Fitbit is underestimating my daily calories burned, when most articles I find are about how this and similar devices tend to overestimate active calorie burn. ![]() Please!! (Other readers: Please keep voting for the original post!) I'm glad this is still "under consideration" but since it's been a year without any additional comments, I'm adding my strong support for the ability to use body fat percentage in Fitbit's calculation of BMR. Using the Aria does not address this issue and users should be able to input their own BF% data to arrive at a more accurate metabolic rate estimate. Right now Fitbit is squandering the data advantage offered by a HR monitor that measures activity levels.Įdit: Also, BF% based on electrical conductivity/resistance measurements such as those provided by scales like the Aria are typically quite inaccurate, although they may be precise in their inaccuracy. This results in Fitbit calorie burn estimates really only working for the median or average female/male user. However, this is a very broad brush to take, as body fat% (and thus calorie burn rate) can still vary quite a bit within a given age+gender+BMI and merely using age+gender+BMI as a proxy for BF%/caloric needs DOES NOT satisfactorily account for this variability. ![]() Right now I assume Fitbit uses your age, heart rate data, and BMI, and then will calculate a different estimate for calories burned based on your gender, which is to say a proxy for body fat%- as women will carry more fat/less muscle on average for a given BMI (heigh/weight metric) than men, due to the effect of testosterone on body composition and muscle mass. Obviously if someone hasn't enetered in their Body Fat measurements than it would default to the age/height/weight but please gives those of us with more detailed body info more accurate calorie burn! This can be simply done using a commonly used BMR equation that incorporates body fat. I would like to see Body Fat implemented in the calorie burn estimations because I really feel this will help accurately measure my calorie burn (if for example I weight 250 lbs and have 15% body fat I will be burning way more calories per day by just living than someone weighing 250 lbs and having 30% body fat). But many of us including myself either manually enter in our calculated Body Fat, or they use the Fitbit Aria Scale which automatically calculates body fat and syncs to the dashboard. Of course for people who don't have body fat measurements, it's easy. Problem is calculating BMR with just height/weight/age BMR is a very poor way of calculating it. Right now I believe Fitbit uses your height, age, and weight to calculate your BMR (Basal Metabolic Rate) which is the calories you burn if you did absolutely nothing all day just by living and breathing and then adds calories burned due to steps/activity/heart rate to that. ![]()
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