Re: weight loss and respiration

[John Denker <jsd@MONMOUTH.COM>]

At 08:19 AM 12/12/00 -0600, Joel Rauber wrote:
> I breath in O2 and exhale CO2.

That's true as far as it goes, but it's not the whole story.

>  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.

The conclusion is true, but it does not follow from the argument given.

> 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.

The metabolism of carbohydrates is particularly easy to understand.  The
name tells the tale:  they are all of the formula C_m (H2O)_n --- so it
takes m molecules of O2 to metabolize them.  The result is m molecules of
CO2 and n molecules of water.  Virtually all of the CO2 (and perhaps much
of the H2O) is lost by respiration.

The metabolism of fats is only slightly more complicated, and understanding
it at this level of detail doesn't require anything beyond high-school
chemistry.  Olive oil contains among other things
        C_3 H_5 (O C O C_17 H_33)_3
i.e.    C_57 H_104 O_6

which requires 80 molecules of O2 if my count is correct.  The result is 57
molecules of C02 and 52 molecules of water.

Again, virtually all of the CO2 (and perhaps the H2O) is lost via
respiration.

**** Do not neglect the loss of H2O via respiration, especially during the
winter.  Think about how much water you need to drink when you are skiing. ****

>>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.

That's absurd.  It's true that breathing produces a loss, not gain, but
it's silly to think that other processes "are a wash".  For starters, how
about weight loss by metabolism of stored carbohydrates followed by
urination of the resulting H2O?

=============================

Trying to figure "weight gain" by simply auditing the weight of inputs and
outputs is a pointless exercise unless you are prepared to do a _really_
meticulous audit.  The level of detail being discussed in this thread is
not nearly meticulous enough.  For one thing, much of the food is water,
and nobody AFAICT has proposed auditing the water budget (let alone
proposed a _means_ for doing so).

And what, pray tell, is the action item?  Do we want students to think
that, as a practical matter, eating a pound of celery is the same as eating
a pound of butter?  Do we want them to think that they can slim down if
they just breathe more?

Or are we trying to conduct a case study in bad experiment
design?  Why?  Isn't there enough of that already?