how much can basal metabolic rate vary?

The Gist said:

However, how much variation can there be? For
some people in my age group at my weight, etc is it possible that there
basal is 20% lower? 50%? What is the natural variation within a group of
people with the same basic factors in common.

There wouldnt be any 'variation' between people of the same age, weight
etc (if all common denominators are the same) as these are based on
stat charts/graphs/collections etc of similar data. Its just a
recommended target range and really nothing more. This reminded me of
when a a friend measured her bodyfat the day before her birthday and it
was 18% - if she factored in her age change to one year older, it told
her she had 20% bodyfat. So similarly, its based on collected data, not
reality.

Quoted message said:

Relatedly, would there be a similar variation in how much energy is
expended during excercise for people with the same age, weight, height

That is about the only variable, and most programs ask you how active
you are, or track your exercise intensity, to determine this. Remember
that as you lose or gain weight(bodyfat)your BMR will change as you
change, so if you have been at this for awhile, it would be good to
recalculate it if FitDay doesnt adjust it for you as you get closer to
your goals. Here is a good site which has a BMR calculator (2nd topic
from the bottom) that would be good for comparison:
http://www.hussman.org/fitness/

joanne

"joanne" <[email hidden]> wrote in message
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Quoted message said:

The Gist said:

However, how much variation can there be? For
some people in my age group at my weight, etc is it possible that there
basal is 20% lower? 50%? What is the natural variation within a group of
people with the same basic factors in common.

I think this is a great question

Quoted message said:

There wouldnt be any 'variation' between people of the same age, weight
etc (if all common denominators are the same) as these are based on
stat charts/graphs/collections etc of similar data. Its just a
recommended target range and really nothing more. This reminded me of
when a a friend measured her bodyfat the day before her birthday and it
was 18% - if she factored in her age change to one year older, it told
her she had 20% bodyfat. So similarly, its based on collected data, not
reality.

I'm sorry, but this makes no sense to me. As I understand it, the BMR is an
attempt to measure how many calories that an individual uses during a day
at rest. Of course, this would have to be an average, and whatever
calculations that Fitday uses would have to be a rough approximation. There
is no way to account for every relevant variable, even if they were all
known. Even the food you eat and the timing of meals can vary your BMR.
So, if your calculated BMI is an average, then there should be some idea of
the standard deviation of the population's BMR. The SD might be quite
large, but still it would be interesting to know.

In case you care, standard deviations show how well the "average" given
represents a sample. Consider a sample of 2 numbers, 1 & 99. The average
is 50, but who cares? The satndard deviation is so large that the average
is useless. Consider another sample, this time of 49 &51. The average is
still 50, but this time the sd is small, and so the average actually tells
you something. If in this case we found that the average that fitday
calculates has a sd of 100, that would mean that about 66% (I think that is
the right number.....) of all people would be within 100 calories of that
number. 95% of all people would be within 2xsd (200, in this case) of that
number, and 99% would be within 3 standard deviations.

I looked around and found this:
http://www.fao.org/DOCREP/003/AA040E/AA040E15.htm
The RSD column is the standard deviation from the formula that they use.

jeff said:

If in this case we found that the average that fitday calculates has
a sd of 100, that would mean that about 66% (I think that is the
right number.....) of all people would be within 100 calories of
that number.

If you assume normal distribution the area under that curve from
Mean-StdDev to Mean+StdDev is 68%.