Amadeus wrote:
>Yes, that's right. According to my reading humans dont have the ability
>to use purins as a nitrogen- (protein-) source opposed
>to hunting animals (as cats), who *can* use it.

I'm not sure what you mean.  Aren't purines used as, er, purines?  More
accurately, the addition of a ribose or deoxyribose sugar to a purine forms
a nucleoside, and the triphosphate form of at least a couple of these
nucleosides are a critical component of energy production.  For example, the
nucleoside form of adenine (a purine base) is adenosine, and adenosine
triphosphate (ATP) is the principal energy carrier of our cells.

I'll repeat a quote from my original post: <<Purine and pyrimidine bases
which are not degraded are recycled - i.e. reincorporated into nucleotides.
This recycling, however, is not sufficient to meet total body requirements
and so some de novo synthesis is essential.>>  We _need_ purines.  The
question is whether de novo synthesis (which is energetically expensive) is
a sufficient or desirable means of fulfilling this need.

>I did mention this primarily as a reason not to eat protein as a
>*caloric* supply.
>There are good caloric supplies without purins - fat and carb.

I try not to depend on those foods, since I _want_ purines. ;-)

>[...] But if you compare purins comeing from plant protein or from meat
>that's not so much of a difference (50-70 percent).

The difference can be either small or large, depending on which two foods
are compared with one another.  Someone posted a list of foods categorized
by purine content at http://bcn.net/~stoll/wwwboard/messages/9617.html.  The
purine content of plant foods is 0 -150 mg/100g, and 50 - 825 mg/100g for
meat (the difference may be even greater, since the table isn't that
precise).

>[...] One exception btw is dairy protein (curd cheese) as long as it's
>not processed by bacteria (sour). Here you have pure
>animal protein without genetic information -purins- accompanied with.
>Apparently a calve or a human (or a tiger ?) doesn't need it to grow big.

Eggs are another example of a food low in purines.  I would expect a yolk to
contain plenty of genetic information, so this fact confuses me.

>If it was from purins, then you should get a maximum of
>energy
>level from maybe chicken skin. Or Kidney.
>So maybe it's something else especially in the read meat that gives you
>your desired energy level.

Yes, organ meats do give me a lot of energy.  Thank you for asking. ;-)
Ditto for skin, though I hadn't realized that skin was a good source of
purines; I thought that I simply benefitted from the fat.  Although red meat
is my favourite, _every_ source of dark meat (including tuna, mackerel, and
the dark meat of fowl) gives me more energy than does white meat.

Cheers,
-- Aaron Wieland