On Tue, 6 Jun 2000, Amadeus Schmidt wrote:

> >.. Lyle is allowing for a period of adaptation, after which
> >the brain's ability to use ketones is greater.
> But I'm shure it isn't really tested.
> You can count, how much carbohydrate you eat, and estimate how much
> energy the brain uses. But only roughly estimate, how much
> glucose comes from degraded protein, and how much from ketones, then.

The amount of glucose that comes from ketones is zero.  I think
gluconeogenesis output rates can also be measured to some extent.
In addition there is the fact that many people experience an
initial period of "brain fog" when in ketosis, which goes away
after a week or so.  This also suggests adaptation to the
different fuel mix of more ketones and less glucose.

> >I'm not sure.  I think muscle glycogen is also gradually
> >replenished.  People on zero-carb diets do eventually regain the
> >ability to do high-intensity exercise, but it takes time. ..
>
> This would even elevate the actual glucose needs for the muscles.

Yes, high-intensity exercise definitely increases glucose demand,
but here again there is an adaptation effect.  Fast-twitch muscle
fibers must burn glucose, but in a trained person these fibers
are recruited mainly for maximum-intensity anaerobic effort.  In
an untrained person the fat-burning slow- and intermediate-twitch
muscles are less efficient, so the fast-twitch muscles get
recruited anyway.  Thus, when an untrained person tries to jog,
he will soon experience "burning" in the legs, a sign that
lactate is being made, the by-product of glucose burning.  He
will probably also soon feel the need to urinate, since the water
molecules attached to the glycogen are released in the process.
As the person becomes conditioned, this goes away.  The
fast-twitch muscle fibers are no longer being used to any
significant extent; a higher ratio of fat to glucose is being
used.

This is why high-intensity exercise is good for people with
insulin resistance.  It tends to deplete liver and muscle
glycogen levels.  When carbs are finally eaten, they are
immediately sent into the glycogen "bank", causing only a small
change in blood glucose.  When liver and muscle glycogen stores
are already (and chronically) full, most of the incoming carbs
must be converted to fat.

> I think it does *not* mean how it may look first place, like
> "keep quiet, if you don't know about something".
> This i'd translate to
> "Worueber Du nicht Bescheid weisst, solltest Du nicht reden"
> (But maybe this would be also wise).

I was being facetious.  In fact, Wittgenstein was asserting that
the relation between language and the world is itself something
that lies beyond language, and therefore we cannot speak
coherently about it.  Therefore, "davon muss man schweigen."  It
was a call for philosophy to recognize its limits.

> >PET scans show increased energy utilization in parts of the brain
> >that are "busy", which shows that heavy thinking (Schwer denken?)
> >indeed burns more calories than daydreaming.  But it doesn't burn
> >*that* much fuel, or there would be no fat philosophers.
> ("schwer denken" is in my feeling impossible,but closer to "tired thinking"
>  I'd translate "intensives (nach-)denken" or "starke Kopfarbeit")

Perhaps "schwer denken" is a good description of the "brain fog"
that some people experience when they first enter ketosis.

Todd Moody
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