Age dependancy on BMR

yirara

Wow, I've just been playing with the scooby calculator and saw something I've not noticed before. I was wondering how people smaller and lighter than me can have a BMR way above me... until I realized I forgot to fill in my age.

age 20: 1464
age 40: 1370

As I am 40 that explains something. At this age however, I'm fitter than I've ever been in my life and have more muscles. Of course this is all an estimate, but what is the assumption behind the lower BMR with age: only the assumption that older women are less likely to have muscles and work out, or something else?

psuLemon

In the grand scheme of these 100 calories is almost nothing.


To answer the question though.. muscle loss is probably the big assumption

shadow2soul

It's the method of determining BMR. There are multiple. That page is set up with the Harris-Benedict Formula. There is also Katch-McArdle, Cunningham, and Mifflin St. Jeor.

If you go to scoobys Accurate Calorie Calculator, you get to choose the method used. Katch-McArdle and Cunningham use BF% in their formulas.

yirara

Yes, I know shadow2soul. But both equations take age into account:
Harris-Benedict female 655 + 9.6*Weight + 1.8*Height – 4.7*Age
Mifflin-St Jeor female 9.99*Weight + 6.25*Height – 4.92*Age -161

And for other methods that are probably more accurate you need to know your lean body mass, which I don't. I'm mainly interested in how age plays a role.

shadow2soul

It's odd, with 2 methods age makes a difference and with the other 2 age changes nothing.

I'm going to guess it's what psulemon said.

Oh here...page 107 is where they start the discussion about age and metabolism:
A biometric study of basal metabolism in man by Harris, James Arthur and Benedict, Francis Gano

psuLemon

I assume the methods that aren't adjust by age are based on body composition? Like katch mcardle? In the end, lean body mass is a better statistical predictor.

shadow2soul

psulemon wrote: »

I assume the methods that aren't adjust by age are based on body composition? Like katch mcardle? In the end, lean body mass is a better statistical predictor.

Yep. Katch and Cunningham.

bonniejo

If you know your LBM use Cunningham. Age and gender don't matter. 500+22*LBM (edit, LBM in kg)

yirara

Yep, I guess those based on LBM are more better, though I simply don't know what mine is. The usual calculations based on the circumference of certain body parts still puts emphasis on a relatively equal fat distribution even though more rounded hips and thighs seem to have been taken into account somehow. But that doesn't work if you have wide hip, ribcage and shoulder bones and a stomach as flat as possible with that setup - and all the padding sitting on the legs and arms. But that's sidetracking the topic.

bonniejo

yirara wrote: »

Yep, I guess those based on LBM are more better, though I simply don't know what mine is. The usual calculations based on the circumference of certain body parts still puts emphasis on a relatively equal fat distribution even though more rounded hips and thighs seem to have been taken into account somehow. But that doesn't work if you have wide hip, ribcage and shoulder bones and a stomach as flat as possible with that setup - and all the padding sitting on the legs and arms. But that's sidetracking the topic.

Yeah, I get mine taken on one of those fancy impedance scales at the chiropractor about once a month. It likely overestimates a bit because I'm heavier on bottom than top, but I work with what I've got! Maybe your gym has one?

yirara

No, I don't have a gym and cannot buy a caliper in this country or have one shipped over. Those impedance scales probably overestimate bigtime for me.