Message-Id: <3.0.32.19970416224203.006e3764@icefog.polarnet.com>
Date: Wed, 16 Apr 1997 22:42:33 -0800
To: pinhole@exploratorium.edu
From: "J. Lahr" <jlahr@polarnet.com>
Subject: Moose Calories?
I've learned a bit more on the question of determining Calorie content
by burning food, thanks to a few biologists. The conclusion is that
burning a substance could give an over estimate of the number of Calories
that a person would gain from eating the same substance, because if we
can't digest the substance then it won't make us fat. The extreme example of
gasoline was already given, but wood or grass would be a less obvious
one.
I found that microbes can play a role in this. Wood and
other plant materials containing cellulose will burn well but
people can't digest cellulose. It turns out that even
animals like moose, cows, and termites need some help with this.
I made a search on AltaVista found a site
http://commtechlab.msu.edu/CTLProjects/dlc-me/zoo/zatmain.html
at Michigan State University with the following information:
"Cellulose is the strong material in plant cell walls that makes
plant stems stringy and tough so that they can stand up. Cellulose
is difficult to break down, so animals that eat lots of plants (like
cows) have a hard time digesting their food. Some microbes living
in the stomachs of many plant-eating animals can easily break down
cellulose, and in so doing provide the animal with food that it can
use."
"You probably thought termites digested wood. They don't, but the
microbes that live inside their guts do. By digesting wood bits,
the bacteria and protists in the termite's guts help the termites
survive. In turn, the termite gives the microbes a comfy place to
stay."
I suppose if we could digest all of the cellulose in an apple or a
carrot, then they wouldn't be as good for us as they are.
John
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