On Thu, 12 Jul 2001 13:20:56 +0200, Paul Sand <[log in to unmask]> wrote:

>Can body use the dietary protein both as direct energy source? I found such
>a statement in some publications.
>
>I thought that protein is used to make glucose through the process of
>gluconeogenesis and than glucose is used as energy source.

Different amino acids have slightly different pathways into the
citric acid cycle to get energy.
Some amino acids have to go through the glucose stage
some others (3 I think) enter afterwords (and therefore don't require the
possibly limited pyruvate stage).
However all amino acids have to be degraded to some carbohydrate form
(glucose or other). This is gluconeogenesis, isn't it?

And only the carbohydrate part is used, the nitrogen part is cut off and
has to be excreted. What puts some workload on kidneys and other organs.

>If so is it a efficient process and can it supply large energy portion or
>should it be treated as marginal?

I'd say in no way marginal (many of us can tell).
The question is, how much nitrogen excretion and acidity load
humans can stand for a long time and under which conditions.

>If Paleo men sometimes was forced to live on up to 50% of calories from
>protein (as many Paleo authores suggest) it may be true but I just wonder
>how. Are amino acids burnt for anergy or what?

The Speth analysis often quoted by Loren Cordaine specities an upper limit
of about 35% of all calories from protein (in the long term).
From statistical data from existing h/g.
Short term up to 50% may be tolerated.

There is such a thing like protein toxicity (rabbit starvation) which
limits the protein percentage and it comes from the toxic waste of the
protein decomposition.

However is see that many Paleo authores suggest the calories from
protein to have been permanently at the upper physiological limit
(35 or even up to 50%).

If you look at paleo-possible food items, meat or plants, you find that the
protein part indeed is higher as most modern food items.

E.g. fruit - a really native food source
the relation (in weight) of protein to carbohydrate  to fat is about
1 : 4 : 1/4
For many berries - wild fruit.
The carbohydrates would be associated with fiber and have much good
fructose.
Modern fruit (e.g. Oranges) decrease the protein part to 1: 10.

Then vegetables (e.g. chimps eat a *lot* non-fruit)
Take fennel/zuchini etc as example. The ratios are somewhat :
1: 1.5 : 1/10
-- much closer, thats near 30% calories from protein.

Nuts have
1: 0.75 : 4 - and fat has double energy per weight.

And meat ranges from 1:0: 0.0something to any ratio depending on fat
available. Deliberately eating persons - Inuit and Stephansson - prefered
about the equal weight of meat to fat, meat has 20% protein so it is
1 : 0 : 5   or some 10-20% calories from protein.

Wild nutrition has higher protein parts as usual today.
Man varied diets tended to increase the energy part largely.

Amadeus