Todd, all this sounds great, and I don't have the scientific knowledge to
discuss this at any level of detail.  But I still have observed that people
CAN and DO lose weight on very high carb diets (usually low fat, high carb).
How do you explain this?  According to what you write here, it would seem to
be impossible.

In a message dated 1/29/2002 9:44:29 AM Eastern Standard Time,
[log in to unmask] writes:


> On Sun, 13 Jan 2002, matesz wrote:
>
> > Todd Moody <[log in to unmask]> wrote:
> > >According to Walsh (http://www.zonehome.com/met/met.htm), we use about
> > >180g of glucose per day, mostly by the brain and red blood cells.  That
> > >would vary somewhat by body weight, because of differences in blood
> > >volume, but not all that much.  Utilization of glucose by the brain
> > >should not vary much either.  So I take this to be a ceiling value:
> > >anything more than 180g/day is converted to SFA anyway.
> >
> > My reply:
> > That sounds arbitrary.  Whether carbohydrates consumbed above 180 grams
> per
> > day are turned to fat or burned for energy would depend on several
> factors:
> > 1) the person's daily energy (kcalorie) needs; 2) activity level, body
> > weight, and muscle mass; 3) whether muscle and liver glycogen stores are
> > full or empty; 4) what else the person eats that day.... 5) total calorie
> > intake for the day, and perhaps other factors not mentioned.
>
> If one is routinely eating more than 180g of carbohydrate per
> day, glycogen stores will be pretty much continuously full,
> except in the morning.  Energy needs are not as important as
> *glucose demand*, and glucose demand comes mainly from brain
> tissue, red blood cells, and fast-twitch muscle.  So activity
> levels would affect it somewhat, especially high intensity
> activity levels.  Conditioned muscles tend to use *less* glucose
> and more fat.
>
> Note that I am not saying that carbs above 180g must be turned to
> fat and then stored in adipose tissue.  Your "turned to fat or
> burned for energy" leaves out the third option, in which glucose
> is turned to fat *and* burned for energy in that form.  Even a
> eucaloric high-carb diet will result in a lot of glucose being
> converted to (saturated) fat, and then burned for energy in that
> form, although there would be no net gain in body fat.
>
> > If a person stays with his or her daily calorie requirements but eats 200
> or
> > even 300 grams of carbs per day, there is no reason the body would
> convert
> > it to fat if the body can use those calories for energy.
>
> Yes there is.  The reason is that blood glucose must be kept
> within narrow bounds, and incoming glucose can only have three
> fates: (1) It is taken up by tissues immediately and used for
> energy; (2) It is stored as glycogen; (3) It is converted to
> saturated fat as circulating triglycerides, which either get used
> for energy or eventually stored in adipose tissue.  If the person
> stays in energy balance, storage in adipose tissue should be
> minimal.  Concerning (1), the tissues that can use glucose
> immediately can only do so at a rather steady rate, which Walsh
> estimates to be 7.5g/hour.  Lutz estimates 8g/hour.  As stated
> above, these tissues are mainly brain, red blood cell, and
> fast-twitch muscle.  High-intensity exercise definitely increases
> the glucose utilization rate somewhat, although it probably
> doesn't affect the daily net utilization that much since
> high-intensity exercise is of short duration.  But I grant that a
> person who engages in a form of exercise with plenty of short
> bursts of extreme exertion, such as tennis or karate, is going to
> burn up more glucose.
>
> Concerning (2), a person eating 200g to 300g of carbs per day is
> going to have full glycogen stores most of the time precisely
> because of the rate-limited nature of option (1).  But there will
> always be some clearance in the morning.  If you eat dinner at
> 6:00pm, by 10:00pm your blood glucose will start to fall, and you
> will have to start drawing glycogen out of storage to keep it in
> range.  If you don't eat again until, say, 7:00am, then that's 9
> hours of continuous glycogen draw, using about 65-70g of glucose.
> So there will then be that much "clearance" for new glycogen
> storage.  That means that if you ate 60g of carbs at breakfast,
> whatever was not soon used by tissues (in three or four hours)
> would go straight into glycogen storage, without any insulin
> spike.  But this wouldn't work at lunch and dinner, because the
> glycogen stores would not then be able to accept much more
> glucose.
>
> This, incidentally, appears to be the key to the Hellers'
> "carbohydrate addict's" diet.  By allowing a single high-carb
> "reward meal" per day, the diet creates a large glycogen
> clearance, so that the extra carbs go right into the glycogen
> bank without causing an insulin spike.  It doesn't have to be in
> the morning, since saving it until evening only increases the
> glycogen clearance.
>
> Certainly the 180g/day rate is not absolute, for reasons that we
> both mentioned, but the point is that it doesn't vary all over
> the place.  A person wanting to reduce SFA load will not want to
> eat much more than 180g/day of carbs, in order to avoid forcing
> the conversion of glucose to fat.
>
> Todd Moody
> [log in to unmask]
>