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weight loss and respiration (was: Mass/Energy Conservation)



Several people have responded with comments somewhat similar to the one
below. I'll give you my take on the issue, which is less authoritative than
the responses below. I am no biologist, and certainly I am not even an
amateur in the study of metabolic process nor do I even play one on TV.
With all the disclaimers, here it goes.

I very naively thought in terms of, I breath in O2 and exhale CO2. If this
happens on a one for one basis than that part of the process is a net loss
of mass, therefore the act of breathing can't produce a weight gain.

I do have relatives with significant knowledge in medicine and biochemistry
and posed the question to them. The response is that this isn't a simple
question. There is no one reaction to which you can assign the incoming O2,
so the above isn't necessarily happening on a one for one basis.

C6 H12 O6 + O6 ---> 6CO2 + 6H2O

Doesn't this mean that all of the oxygen breathed in gets exhaled?
Wouldn't this be a net loss (both for the carbon and the water vapor)?

Incoming O2 may be used in other processes as well.

In the simplest terms, all of the weight that we gain comes from the food
that we eat, and all of the weight that we lose leaves in the air that we
exhale. All of the other inputs and outputs are a wash.

I like this response and it was (and is) my gut feeling; but it is quite
susceptable to a "why?" response, as one should have some reasons as to why
the mass output is greater than input in the act of breathing.

Joel Rauber
Joel_Rauber@sdstate.edu

-----Original Message-----
From: phys-l@lists.nau.edu: Forum for Physics Educators
[mailto:PHYS-L@lists.nau.edu]On Behalf Of Larry Cartwright
Sent: Monday, December 11, 2000 10:23 PM
To: PHYS-L@lists.nau.edu
Subject: Re: Mass/Energy Conservation


Joel Rauber wrote:
... I came up with the idea that we breath and perhaps that
respiration might involve a net gain in mass through respiration
combined with digestion. Which gets down to whether or not digesting
your food might combine with some of the mass you input through the
lungs with what you input in your stomach making for a net gain over
and above the mass input going down the esophagus.

Mass gain in adults is accumulated almost exclusively in the form of
carbon and hydrogen, synthesized into the triacylglycerol (TAG)
molecules that have become known to the general public as
"triglycerides". The adipose "depot fat" tissue (the stuff that
produces the guys' potbellies and what the girls delicately call
"cellulite") is almost pure TAG. A typical TAG is awkward to do in
ascii, but here goes:

(C15 H31 CO2)(C3 H5)(C17 H33 CO2)2

Note that of the 163 nuclei in the molecule, there are only 6 oxygen; to
me that suggests the oxygen we breathe has little to do with weight
gain. Actually, to LOSE mass you have to combine this crud with oxygen
to convert it into C02 and H2O, which is partly why aerobic exercise is
one key to eliminating accumulated fat. It takes approximately 80
oxygen molecules to "lose" a single TAG molecule.

Best wishes,

Larry
(who unfortunately has a close personal relationship with TAG)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Larry Cartwright <exit60@ia4u.net>
Physics and Physical Science Teacher
Charlotte HS, Charlotte MI USA
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~