On Thu, 31 Jan 2002, Amadeus Schmidt wrote:

> On Wed, 30 Jan 2002 11:09:43 -0500, Todd Moody <[log in to unmask]>
> wrote:
>
> >And for emergency exertion.  It makes sense that we have a
> >reservoir of glucose to keep the nervous system going, and for
> >emergencies when we need "turbo-charged" effort.
>
> Ok, that makes sense (glycogen only for high octane purposes).
>
> Particularly if you think of relative frequent starvation times.
>
> But not if you consider the time after eating.
> Then natural carb is high.

During the time after eating, the bloodstream may be flooded with
carbohydrates that must be handled immediately, or else the
elevated blood glucose would be deadly.  If there is room in
glycogen storage, that will be used first.  This is a good reason
to engage in periodic high-intensity exercise, since this also
creates clearance in the muscle glycogen.

> For a well fed primate with good access to good carbohydrates, It would be
> the most common state. Then it would be best to burn  food in the moment,
> without any indirections into storage.

I think the hunter-gatherer way of life entails less continuous
eating than in the foraging way of life common to other primates.
But the conversion of glucose to fat is not a "storage" issue; it
is a way of keeping blood glucose within bounds.  If glycogen
stores are usually less than full, this is less of a concern.
But for them to be usually less than full, one must be eating
less than about 180g/day of carbs.

> I don't believe in a general human tendency to build fat storages "for
> survival". We come from a area with little seasons and are not hibernating.
> Fat storages beyond a few kilos were as unfavourable as today.

Yes, but global cooling did present some fairly severe selection
pressure, and fat does insulate.  It would not be a major genetic
change to select a phenotype that adds fat readily.  But as a
general thing, both fat and glycogen stores are fuel reservoirs
from which energy can be withdrawn as needed, keeping blood
levels of both fats and glucose relatively constant.

> It's a quest to open up the fuel channels into the cells instead of the
> storage.

Yes, and we know that insulin is at least one of the important
controls of this process.

Todd Moody
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