On Fri, 7 Jun 2002, Richard Geller wrote:

> > If your reserves are
> > low,  you will simply run out of glucose before it can be
> > replenished from gluconeogenesis, and you will "run out of gas"
> > during your workout.  I.e., you won't be able to do as many reps
> > or sets as you otherwise could.
>
> Todd, has that been your experience? Others on the list?

It has been my experience and as far as I know it is
an undisputed physiological fact.  Certain cells are absolutely
glucose-dependent.  These include some brain cells, all red blood
cells, and all fast-twitch muscle cells.  The fast-twitch fibers
are recruited during high-intensity anaerobic exertion.  Normally
there is enough muscle glycogen around for this purpose, but on a
very low-carb diet, eventually even muscle glycogen gets sent to
the brain.  This is why bodybuilders will carb up before a
competition, to get rid of the "flat" look that carb-depleted
muscles have.

> I have also heard about people who seem to do quite well in the gym
> supposedly on very low carb, e.g. 30g per day, and wondered if that was just
> a story or if it was true.

I guess it depends on what they are doing in the gym, and how
often they are doing it.  Gluconeogenesis could replenish
glycogen reserves, but it would be slow going since first
priority would go to brain and blood cells.

> I guess runners or other endurance exercisers could function quite well on
> very low carb in that those muscles are slow twitch and can be happy eating
> fat and ketones rather than glycogen?

Yes.  Phinney did studies of endurance athletes (trained
cyclists) who, after about three weeks of adaptation, actually
improved their performance slightly while in ketosis.  The
ability to utilize fat efficiently is a great advantage in an
endurance athlete.

Todd Moody
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