On Tue, 8 Aug 2000 13:11:33 -0400, Todd Moody <[log in to unmask]>
wrote:

>On Tue, 8 Aug 2000, Amadeus Schmidt wrote:
>
>> The brain is dependent on fuel in the form of carbohydrates.
>> The meats have zero carbohydrates, but it
>> could be converted from very much protein of it.
>
>You're forgetting also that the 500 kcal requirement for glucose
>can be reduced in ketosis.  Part of the brain can burn ketones,
>so in ketosis the absolute glucose requirement is reduced, and
>with it the gluconeogenesis burden.

hm hm I thought that in a savannah ketosis would not happen too
often because at least every few days some carb resource would be available
inhibiting ketosis but ok...
For completeness according to your request I would add...

In a situation with close to zero carbohydrates (e.g. < 60 g carbohydrate
per day) as in starvation or when very few carbohydrates in the
diet are available, the brain can resolve its energy demand in about half
from fat, after a few days of adaption.

....

I closer look to Ketosis and savannah evolution time....
I think ketosis is an adaption to survive longer starvation periods without
having to cannibalize too much muscle mass in sustaining brain, nerves and
blood. Other primates have the possibility of ketosis too (when fasting), so
it can't be an adaption to the increased demand of the enlarged brain.
Further ketosis enabled humans to lead a hunting life of meat and fat in
northern latitudes.
Where (all according to Cordaine's kangaroo posting) animals were higher in
bodyfat (15%) so that no additional food energy in form of carbohydrate or
fat addition or discarding of animal parts was necessary to avoid toxicity
of protein (beyond 35% of calories from protein).

According the Stephansson all meat experiment, to Inuit data and to what you
once reported as your own practice, people with free access to both meat and
fat (and no carbohydrate) seem to prefer a proportioning of 600g meat (1+
lbs?) and the rest as about 1/2 lbs of fat.
In calories that is with a few comparisons:
kcal from ! kcal   ! kcal f.
protein   ! f.fat  ! carb
680         2100      60  Todds data
680         2100       0  Stephansson/Inuit
25%           75%      0% Stephansson/Inuit/Todd.. in percent
35%         (     65%   ) Limit of protein toxicity
40%           60%      0% Northern latitude animal (ref Cordaine)
54%           46%      0% Kangaroo (grassland animal example) ref Cordaine
11%          1-5%     88% tubers (e.g.potatoe)

Energy really seems to be the actual bottleneck in a nutrition
in the wild, without plenty of fruit or tubers.
Tightened by the bigger brain.

It was fun studying archeology...

Amadeus