Metabolic variation

September 30, 2005 10:37 AM

How much variation is there in the metabolic efficiency of humans?

For example, if I took a hundred males of the same age with the same weight and same lean muscle mass, how much variation would one expect in their BMR?

Follow-up question: In that variation, what happens to the extra calories in the inefficient specimens? Is it never absorbed from food? Does it get turned into heat? By what process?

posted by justkevin to science & nature (8 comments total)

Are you going to have them all doing the same activities to?
posted by delmoi at 11:09 AM on September 30, 2005

Uh, I found a study about Columbian women. 8% was their intraindividual variance.
posted by GuyZero at 11:19 AM on September 30, 2005

I read somewhere that 35% - 95% was the range of human metabolic efficiency. I don't remember what the variables were in subjects.

This question is further complicated by the type of muscle mass - does fast twitch burn more or less (resting) than slow twitch?

Or how about this: with regard to calories that aren't used by the body, do they pass through the digestive system, or do they get absorbed into the body, say into the blood stream, but don't get used by any metabolic function, and pass out of the blood and on out of the body?

Metabolic syndrome is an unhealthy condition, in healthy people, doesn't the body just ignore some sugar it doesn't need?
posted by ewkpates at 11:45 AM on September 30, 2005

The Basil Metabolic Rate (BMR) is only one measure of the question you appear to be asking. It is a measurement of the body's energy consumption while at rest.

As delmoi points out, the efficiency with which the body performs physical work is another. Athletes like Lance Armstrong have a vastly superior ability to efficiently convert food into miles than most other humans. Part of that efficiency involves being able to keep the body temperature within certain limits, while another part involves how to deal with metabolic by-products such as lactic acid. Armstrong can sustain a power output of over 900 watts, while very fit "normal" cyclists average around 300 - 400 watts.

Finally, another component of the answer has to do with the body's ability to collect O2 from the air, transport it to the working muscles and return the generated CO2 to the atmosphere. A measure of this is called Specific VO2 max and describes the maximum rate of this transfer process which a body is capable of sustaining. Top endurance athletes have values of this between 70-80 while reasonably fit "normal" people have values around 50. A lab I worked in did a lot of research on this and found that training a person from slob to buff usually resulted in an increase of this value of about 10-15%. Thus, there appears to be a genetic component as well as a training component.
posted by RMALCOLM at 11:55 AM on September 30, 2005

I'm pretty sure it's acutally Basal Metabolic Rate
posted by soplerfo at 11:58 AM on September 30, 2005

Haha, 1,080 hits on Google for "basil metabolic rate"
posted by rxrfrx at 12:11 PM on September 30, 2005

My question was prompted by a discussion I had with a friend on how much of a difference genetics makes on body type. If two people with the same weight and lean muscle mass perform the exact same activities, how much difference will there be in caloric requirements?
posted by justkevin at 1:04 PM on September 30, 2005

It also depends on what kind of tasks. I seem to remember having read somewhere that mental excercises consumes very different amounts of energy from person to person, and this can be independent of body weight and muscle mass. I imagine it something like, if you picture a class sitting at an exam, the doofus is getting all hot and sweaty while the brainiak sits cooly and collected blazing away.
posted by Catfry at 1:56 PM on October 1, 2005