On Tue, 10 Apr 2001, Amadeus Schmidt wrote:

> Anything more of protein resulted in more excretion, suggesting usage as
> fuel. Where I can't see a advantage from - but more work for the kidney.
> Or, from more protein maybe more short-lived derivates from certain amino
> acids could be made. Like NO or serotonin.

This is the problem.  You are making two unwarranted assumptions.
First, you are assuming that there is something problematic about
using protein as fuel, but there is no evidence that this is the
case.  The most that can be said is that it is problematic to use
protein as the *only* fuel.  There is no evidence that "more work
of the kidney" is harmful.  The second assumption is that the
other benefits of additional protein--which you mention--are not
significant enough to justify the use of more concentrated
protein sources.  It has become clear, for example, that NO is
indeed an important protein metabolite, and since NO requires
substantial amounts of arginine, the best way to get it is to eat
meat.  Yes, you could get it from peanuts, but you'd need to eat
large amounts of them, and in the process you'd have other
problems.  It's also very interesting that to achieve a balance
of insulin and glucagon, a substantial amount of protein is
needed, a lot more than what is needed simply to achieve nitrogen
balance.  Possibly related to this is Wolfe's research indicating
that higher protein intake improves blood lipids.  Finally, there
is also evidence that greater amounts of animal protein have a
protective effect against osteoporosis, for reasons that are not
yet clear.

I think you have demonstrated that we can get by on less protein.
There are good reasons to believe, however, that we thrive on
more protein, especially animal protein.  By avoiding animal
protein, you probably avoid using much protein as fuel, but I'm
unaware that there is any known advantage to this avoidance.  At
the same time, you limit your body's ability to synthesize NO
from arginine, because most plant proteins are poor sources of
arginine, and you're not getting that much anyway.  You are
making it harder to achieve a balance between insulin and
glucagon, and you may be increasing your risk of osteoporosis.
And you are almost certainly bringing about elevated homocysteine
levels (http://www.sciencenews.org/20010113/food.asp ).

If we look at the whole picture concerning proteins, and not just
the nitrogen balance tests, it's clear that there are more
reasons to consume animal protein than there are reasons to avoid
it.  Even though we are equipped to survive in conditions of
extreme protein scarcity, it doesn't seem like a good idea to
inflict such conditions on ourselves.  And yes, a similar point
might be made about carbohydrates.

Todd Moody
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