Your toughts about BMI vs Body Fat?

Krav

For me BMI is a quite useless number. I know it's widely used but I fail to see why.
This is why:

Two men of equal height, weight and age calculate their BMI. Their BMI will be exactly the same. Say 26, so both of them are overweight according to the BMI scale

Do both need start watching their weight? I think BMI can't tell you that...

Man A is a couchpotato with a pot belly.
Man B is the gym type with lots of muscle and broad shoulders.

As mr-zero-expert I would say man A is overweight, but man B likely isn't.

Not ideal either but I think Body fat is a better way to measure things.
It takes into account neck, waist and hip size on top of the standard BMI variables.

A question about a friend of mine. Vastly overweight by any standard.
Big belly that also hangs down all the way past his crotch.
When using the Body Fat formula as shown in the link below, how would you measure him?
I'm especially interested in the hip.
Would you measure over or under the belly that's hanging there?

Then a last question, where is your hip....?
Just look at these pictures and see the hip is measured at many places.
Halfway your butt. Croth. High hip.
Where should I measure for the Body Fat calculation?

https://www.calculator.net/body-fat-calculator.html

Pangloss

Agreed.

BMI made more sense before everyone started carrying around so much processing power and collecting the relevant data.

Why use a statistical model when we have actual relevant individual biometric data and computers in our pockets?

Yes, daily consumer fat percentage measuring is imperfect, but it's getting better and is relevant if done consistently so that trends can be detected.

It's not just an appearance issue, either, as bone density (or weight, at least), visceral fat, water content, etc., are all health concerns.

Krav

Visceral fat is somewhat part of the weight and even less part of the waist size.
Regarding water, spot on.
I always take my measurements in the morning when I'm as empty as possible.
If I calculate my body fat and then drink 5 glasses of tap water, and then redo the body fat calculation, surprise, my body fat jumped up. But we know as a fact that extra percent isn't fat but the tap water consumed moments ago.

For me it's just a scientific observation. I don't worry about. I just want to know things.
But I know for some people their scale becomes their all knowing god. I think for them (and me) a blog post pointing out limitations, pros and cons, would be a good thing.

BTW, cronometer staff, why isn't the Body Fat calculation done in the software?

Karen_Cronometer

I believe BMI was intended to be used to assess the relative health of a population, rather than individuals. As you mention @Pangloss it is such an easy measurement to take, it gained widespread use for individuals as a proxy for a healthy weight relative to height. It is much more informative to measure fat mass, and lean body mass, if possible, to assess an individual.

You have the option to track your body fat % as a biometric in Cronometer. We don't have a calculation included because it is a more accurate to measure it instead. The formulas to calculate body fat % may not apply equally to all body types.

Best,

Krav

"We don't have a calculation included because it is a more accurate to measure it instead."

But it could be done when the user inputs the needed biometics.
Likewise it could calculate BMI.

Pangloss

Just as a clarification, I wasn't suggesting Cronometer calculate body fat percentage. Rather, if body fat percentage is provided by the user, it would be used by the program instead of BMI. BMR would also use it, if available.

Karen_Cronometer

I misunderstood, apologies. Cronometer doesn't use BMI in any calculations.

Your BMR is calculated from your age, sex and height. It is a great idea to use your body fat %/lean body mass here to make your calculation more accurate!

Best,

Susan_RD_101

@Krav

A person's BMI measure isn't helpful unless it's at extremes and considered in the context of health conditions. That said, BMI was developed by a mathematician and later adopted by health professionals.

Body fat is much more useful BUT, getting an accurate measurement is very difficult. Skin calipers can work if the person is trained, but I prefer DEXA or indirect calorimetry.

If you are measuring waist/hip circumference, measure waist at the smallest part (I can usually tell where this is by looking from the back) and measure hips at the widest part. However, waist circumference isn't really useful when someone's BMI is very high due to obesity.

Kind regards,

Krav

@Karen_Cronometer

"I misunderstood, apologies. Cronometer doesn't use BMI in any calculations"

Maybe so, but it does calculate it, as it's in Settings>Profile.
I have to enter my BMI daily as a custom Biometric to be able to chart it?
Why isn't BMI part of Cronometer's standard Biometric set so it saves me the hassle of entering each day?

Krav

@Karen_Cronometer

"You have the option to track your body fat % as a biometric in Cronometer. We don't have a calculation included because it is a more accurate to measure it instead. The formulas to calculate body fat % may not apply equally to all body types."

Don't the measurements define the body type?
Perhaps meant well by Cronometer, but I consider it a flaw/ommission that Cronometer doesn't calculate it. Now I have to enter all the data on a third party site to calculate my Body Fat %. And that's just a calculation based on my own measurements and won't be worse/better than Cronometer calculations.

See, BMI and Body Fat graphs show two purposes for me:
A] A health indicator. Not accurate because my way of measuring might be wrong.
B] Show progress. So even if my flawed calculation is 10% to high each and every day, I still see a decline in both BMI and body fat.

Karen_Cronometer

Great feedback @Krav! We are collecting these kinds of ideas to improve our biometric feature, including additional biometrics included in the default list. I also love the idea of automatic calculations for well-used metrics like BMI and body fat.

Thanks!