BMR and lean muscle mass in re to calculating calories

[HeidiinTN]

Why doesn't Fitbit take into account my lean muscle mass and body fat % in calculating my BMR? I have consistently been building muscle while decreasing body fat, while staying roughly the same weight or losing(which is on the low side of normal). Everything I read says that a higher % of muscle mass means I burn more calories while at rest. 135 pounds with 17% body fat vs 30% body fat would result in different BMR's. I have felt that may calorie counts and BMR were off from day one, and I have a feeling it is because I have more lean muscle mass that is not being considered in calculating my BMR. And is there a fix for this? Is there a calculator that can tell me how much higher my BMR is based on my muscle to fat %? If I follow Fitbit calorie recommendation for maintaining my weight, I lose weight. THX!

[Emryz]

Hey guys!

I don't know if this is the correct forum to post it in, but I wanted to tell someone in charge that the kcal calculation for oatmeal - or specifically the one from Penny Supermarkt - is wrong and aparently hindered my weightloss over the course of 3 months.

The food Database in fitbit gives 62kcal for 100g of this oatmeal - scanned the barcode as i do for everything.

The package gives 372kcal per 100g, which is 500% off the Database nutrition facts.

Granted, I should have crosschecked, that's on me. This fauxpas cost me weeks in weightloss, as I consume oatmeal daily in my Proteinshake, which clocks in at about 506kcal with the Database facts, but at around 880kcal when using the "correct" value, which is nearly 75% more.

How I found out? I plateued for so long I came to the conclusion that my diet has to be off, so I left out all ingredients in my shake one by one over the course of a month - and after ditching oatmeal fatloss started up again.

It was stupid of me to not doublecheck before trying it this way, but the database was pretty accurate so far for everything else.

Well, I hope someone working with the Database reads this post. I made a pic of the barcode to crosscheck/edit the reference.

https://imgur.com/HRQBG5w 

Have a great day everyone! You got this!

Much love

[SunsetRunner]

I've recently found this site has some terrific calculators including body fat....grab a measuring tape and hit the site...good luck! https://rb.gy/wkr6td

[Heybales]

They don't because you'd have to be at the extremes to have a major enough difference in calories to matter.

Considering nutrition labels are allowed to be upwards of 20% off of reality, you'd really need a difference of more than 5% in BMR to be meaningful, and again, unless you are just at extremes, you won't be.

Also, most people don't have a good way to get an accurate BF% estimate.

The BIA scales are at best 10% accurate if you happen to present the exactly same hydrated body to it (water is LBM after all), and that is highly unlikely. They are great for months of figures to indicate direction, they are terrible at anything less to be used in math.

So that's the why. Unless someone is in or been in an extreme diet, vast majority are within 5% of Mifflin, unless at the extremes, like healthy weight but very muscular or fat (skinny-fat), or very obese.

For you to compare between Mifflin (which Fitbit uses something close to it) and Katch-Mcardle (using BF%) BMR calc's:

https://www.calculator.net/bmr-calculator.html

You'll have to click on Settings to select the different calc's to see how much difference between BMR.

For a backup of potential BF% instead of just BIA scale:

http://www.gymgoal.com/dtool_fat.html

And the BIA scales that give BF% reading, only subtract that calculation from total weight to arrive at LBM (Lean Body Mass), which is everything not fat. Again, drink 16 oz of water and you just increased your LBM. LBM is not just muscle mass.

Sadly the ability to gain muscle is very slow, even worse in a diet, so much easier to lose fat.

Recomposition where you do both at same time but maintain weight - even slower.

If the scale is giving a muscle mass reading, it's taken from LBM math and statistics and is even more inaccurate than BF%.

Just to have proper expectations on it, or you could be sadly shocked someday.

[HeidiinTN]

Using the calculators I get roughly the same body fat % as my BF scale. I have been weight training for a while, and I am not sure what is counted as extreme, but I can easily see all the muscles in my body, large and small groups, and I have had measured growth in the larger muscle groups. What body fat % would count as extreme to affect BMR? 

[Heybales]

Depends on age, height, gender.

First link in my message.

Put in stats for the Mifflin BMR - get your figure.

Put in stats for the Katch BMR - get your figure.

Over 5% difference?

Keep changing the BF% on the Katch BMR calc and see where the BMR happens to match, and where it happens to diverge enough to be meaningful.

Now you know for your age and height where the BF% needs to be to be meaningful.

[HeidiinTN]

I did as you said. To get within 5%, I would have to gain 8% body fat. To make them equal, I would have to gain 12%. Which brings me back to my original question— why can’t fit bit include this in their BMR calculations for people like me? Katch bmr has me eating 168 more calories. So without that being integrated I will have to just shoot for 150 more everyday I guess, which sort of defeats the purpose of having Fitbit guiding me in my calorie goals as their red/green/blue zones are meaningless if they are that far off. 

[Heybales]

Why not include option? At this point - money.

Rare usage scenario not worth adding this ability in at this point.

Now, here is caveat to that Katch-Mcardle calculation.

There is a 10% spread using that between men and women, research has shown when BMR (RMR actually) is actually measured.

Why?

Because the 5 most metabolically active organs are larger in avg male than avg female, and they cause the majority of the BMR.

Not surprising, avg size is different, therefore avg sized organs to support that body are different.

But if a man and woman have the same LBM (say 110), unless the man is shorter and woman is taller than avg making those organs about the same size, then it means a woman would have more muscle mass and a man would have larger organs at same 110 LBM.

And muscle just doesn't burn as many calories at rest as those organs do.

So while the calc would spit out the same BMR for 110 LBM, the woman would actually be 2.5-5% lower, the man 2.5-5% higher.

Just to keep in mind as to why these are estimates for everyone, and if you are good about using weight trending apps and known water weight fluctuations, results will eventually beat estimates.

The problem comes in with very variable daily activities compared to pretty set weekly activity schedule.

So away to adjust Fitbit to attempt it starting off right.

The problem is some of these settings changed effect other formula that uses them - like HR-based calorie burn during workouts uses age, BMI (so height & weight), gender, restingHR. Or distance-based calorie burn for daily activity uses gender & height for stride length (that you can manually correct too).

If your workouts are lifting like you mentioned, then that should be manually logged anyway, as HR-based is going to be inflated estimate.

Go back to the calc, Mifflin this time. You know what the target BMR is based on the Katch.

Change the age maybe 10 yrs, change the height up - until you get the same BMR.

There's what Fitbit needs then to start with same BMR.

[Heybales]

Forgot to add.

You'll have to manually correct Stride Length setting now, which is always a good idea anyway for best estimate of daily activity calories.

You'll have to change your HRmax figure, which if you have a better idea than 220-age, is a good idea too for workout calories.

[Dr.Kate · Accepted solution]

@Heybales I believe you're incorrect in the post above saying that the difference in BMR calculated with and without body fat percentage is meaningless for the vast majority... adding my results here for others' consideration. 

My experience has been similar to @HeidiinTN in that I need to eat ~100 kcal/day OVER what Fitbit estimates (using the "sedentary" setting where it starts with estimated BMR and adds calories for activity) just to maintain weight. Most articles I've found are about how Fitbit and similar devices tend to OVERestimate active calorie burn, so I came to the conclusion that it must be underestimating my BMR, and set out to figure out why.

As you mentioned, it seems Fitbit uses the Mifflin-St. Jeor formula to estimate BMR from gender, age, height, and weight. I'm a petite woman, and using that formula, my estimated BMR is ~1150 kcal/day, which matches the basal expenditure that Fitbit shows for me during sleep. 

I've never had a "real" body fat measurement, but using the Navy and Covert-Bailey tape measure methods, which I know have their own inaccuracies, my current estimate is 20-25% which is normal for a fit woman. Using that value in the Katch-McArdle BMR formula, my estimated BMR is 1250-1300 kcal. That difference matches my trial-and-error Fitbit experience very well, so I expect the tape measure BF estimates are good for me. 

Playing around with different body fat values in the Katch-McArdle formula, I have to enter a value of 33% with my weight in order to match the Mifflin-St. Jeor estimate for women. So, in my height/weight range anyway, Fitbit assumes a body fat of 33%. Depending on whose published ranges you read, 33% for women is borderline or overweight, which may in fact match the "average" American population that Mifflin-St. Jeor is estimating. 

The reason I'm responding to this post is that Heybales asserted the difference between Mifflin-St. Jeor and Katch-McArdle BMR estimates would only be meaningful at extremes of diet and body fat percentage, and I don't think that's an accurate assessment. At 20-25% I am not extreme, and my current goal is to maintain weight (or gain a bit while building muscle). The difference in estimated BMR using these two formulas is only 10%, but that's large enough that if I follow Fitbit's recommended maintenance intake, I will have an unintentional deficit of 100 kcal/day and lose weight while having difficulty building muscle. Similarly, someone with a body fat of 40%, which is overweight but not extreme, would get an overestimated BMR and would probably find that they don't lose weight following Fitbit's recommended intake until they set a surprisingly large calorie deficit. (You'll find exactly that lament in a number of community posts.) 

Now that I've done all this calculation, I can play a constant mind game of aiming 100 kcal over Fitbit's recommendation, ignoring the built-in gauges and guidance. But it sure would be easier if Fitbit allowed the option to incorporate body fat percentage in its BMR calculation. I disagree that it would be a "rare usage scenario" because I'm not an extreme case, and it would be meaningful for the two groups Fitbit targets most: fitness enthusiasts who probably have lower than average body fat, and those seeking to improve fitness who have higher than average body fat.

For anyone else who agrees, this link is a feature request someone else posted to have body fat percentage as an optional input to BMR, please go vote for it! https://community.fitbit.com/t5/Feature-Suggestions/Incorporate-Body-Fat-into-BMR-RMR-calculations/i... 

[Heybales]

So BMR increases 100-150 calories with different calc.

Putting that many calories into perspective, that is 7.7% of the Katch BMR.

About 6.2% of a sedentary daily burn.

If not sedentary, even less % of daily burn.

Food labels are allowed to be upwards of 20% inaccurate for calorie count by allowed rounding and methods of adding up ingredient calories.

I just mean in the scheme of unknown inaccuracies for most the difference is outweighed by other inaccuracies.

All the estimates (and they all are, some better than others) mean that in the end - adjustments based on real world results will be required.

Just like you did.

Sadly I'm very doubtful many would understand how to do that, or take the time.

Yes, this would be nice if they would help you to use a decent BF% value in the calculations - but how many people would jump on a BF scale and trust the 10-20% inaccuracy of that device, use that as a bases, and get an eating goal even further off than 5%?

A way of taking your daily eating totals and weight change could be useful too - but now you have the issue of basing calories on potential water weight changes that has no bearing - but I'd wager majority of people don't know that either and would log an invalid weigh-in day.

Fitbit as others is stuck with trying to keep it simple, while protecting some people from themselves and not getting complaints more than they get.

It would be nice option if several explanations could be given before checking the box and entering the BF% - if people would read it. You can probably guess I have little faith in that happening.

[CGrimes]

Use the USNavy Body Fat calculator to figure out your body fat and lean muscle mass. Those are the two most important things in body transformation. The scale tells lies, just like BMI is only a weight to height ratio.