Gluconeogenesis - does it normally occur?
bert hubert
In my quest to lose weight I'm trying to understand how my metabolism works.
I find that it helps me keep up my improved eating habits.
Now, I'm busy reading _Advanced Nutrition And Human Metabolism_ (Groff &
Gropper), and I have a question about gluconeogenesis.
Does it occur in healthy people who are losing weight? On the one hand, you
would guess that it would, but I'm not sure. I read that the glycemic stores
'contain enough energy for a day', and they are normally quite full, which
would lead me to think that gluconeogenesis is generally not needed. This
question is obviously only relevant when eating a regular diet, not low-carb
or whatever.
This ties in more or less to a strategy question - parts of the body can
live on glucose or fatty acids, or even ketones, so in a sense there is a
choice. Except for the brain and testes and some other parts, the body can
burn either fatty acids or glucose - which does it prefer?
Am I right in thinking tha ketone burning is a last-resort thing, which is
not likely to occur in healthy people who are not fasting?
Thanks for your time. I'm happy to see that there is a busy group about this
subject which is not geared solely towards dieters and bodybuilders! There
is so much nonsense information out there that is scares me.
Regards,
bert hubert
Tecaddict
gaining weight.
"bert hubert" <a...@ds9a.nl> wrote in message
news:slrna3he...@hubert.ds9a.nl...
Paul Rogers
>
> In my quest to lose weight I'm trying to understand how my metabolism
works.
> I find that it helps me keep up my improved eating habits.
>
> Now, I'm busy reading _Advanced Nutrition And Human Metabolism_ (Groff &
> Gropper), and I have a question about gluconeogenesis.
>
> Does it occur in healthy people who are losing weight? On the one hand,
you
> would guess that it would, but I'm not sure. I read that the glycemic
stores
> 'contain enough energy for a day', and they are normally quite full, which
> would lead me to think that gluconeogenesis is generally not needed. This
> question is obviously only relevant when eating a regular diet, not
low-carb
> or whatever.
Exercise comes into the picture as well, and the bottom line is that if you
do not have enough glucose available from carbs or storage, protein (either
dietary or muscle) or stuff like lactate will be used as a substrate to
produce glucose and feed the brain, testes, kidney etc.
> This ties in more or less to a strategy question - parts of the body can
> live on glucose or fatty acids, or even ketones, so in a sense there is a
> choice. Except for the brain and testes and some other parts, the body can
> burn either fatty acids or glucose - which does it prefer?
Both. At low intensities of energy requirements fatty acids and circulating
glucose; at higher intensities stored glucose (glycogen); at longer
duration, fatty acids and glycogen.
> Am I right in thinking that ketone burning is a last-resort thing, which
is
> not likely to occur in healthy people who are not fasting?
Probably occurs in endurance exercisers, eg, marathon runners when all else
is gone! Under normal conditions of daily nutrition though I would expect a
liver dump of stored glucose to be sufficient to prevent ketosis between
meals or overnight. Could be wrong though. Depends on how much you eat and
burn.
Paul R
bert hubert
<00E16210F79B24E7.77382742...@lp.airnews.net>, Howard
Lee Harkness wrote:
> bert hubert <a...@ds9a.nl> wrote:
>
>>Does it occur in healthy people who are losing weight? On the one hand, you
>>would guess that it would, but I'm not sure. I read that the glycemic stores
>>'contain enough energy for a day', and they are normally quite full, which
(...)
>
> The liver converts a little over half of all dietary protein into
> glucose in all normal, healthy people. The percentage will vary a
> little, but not a great deal.
Thanks. I understand that normally protein is not a major contribution to
your caloric needs, however. I get the impression from responses that
gluconeogenesis (I still wonder why it is 'neo' - any genesis looks like
'new' to me) does occur in healthy people who are losing weight.
I read elsewhere that the brain requires in the order of 100 grams of
glucose/day, which combined with other glucose needs may well mean that even
when well fed, extra glucose is needed to keep everything running (or so I
speculate as an amateur).
Regards,
bert
Jay Tanzman
bert hubert wrote:
> I understand that normally protein is not a major contribution to
> your caloric needs, however.
This is not correct. With a few exceptions, you must burn an amount of protein equal to the amount
you eat (absorb, actually). If you didn't, where else would it go?
> I get the impression from responses that
> gluconeogenesis ... does occur in healthy people who are losing weight.
No, this is not correct either. Most amino acids are "glucogenic." Their normal dispostion is to
be converted to carbohydrate-like compounds (gluconeogenesis) and burned as carbohydrates would be.
Some amino acids are "ketogenic" and are converted to ketones before being burned.
-Jay
bert hubert
> Most people enter ketosis everyday. The only people who don't are those
> gaining weight.
Sure?
'... Such a situation would occur in diabetus mellitus, starvation or simply
a very low-carbohydrate diet.
The inadequate supply of carbohydrate reduces the pool of oxaloacetate
formed mainly from pyruvate, with which the actyl CoA normally combines for
Krebs cycle oxidation. As carbohydrate use is diminished, oxidation of
fatty acids accelerates to provide energy through the production of Krebs
cycle substrates (Acetyl CoA).
This shift to fat catabolism, coupled with reduced oxaloacetate
availability, results in an accumulation of acetyl CoA. A sharp increase in
ketone body formation follows as would be expected, resulting in the
condition known as Ketosis'
Doesn't sound to every day to me?
Groff & Gropper continue:
'Ketosis can be dangerous in that it can distrub the body's acid-base
balance (two of the ketone bodies are, in fact, organic acids). Howevever
the liver's ability to deliver ketone bodies to peripheral tissues such as
the brain and muscle it an important mecahnism for providing fuel in
periods of starvation. It is the lesser of two evils'.
So it appears that ketosis would only occur when there is an energy need,
but no substrate for gluconeogenesis.
I'm confused - if you can elaboratem that would be wonderful.
Regards,
bert
Paul Rogers
news:877B993D3BBEC459.4FDAE7F8...@lp.airnews.net...
> bert hubert <a...@ds9a.nl> wrote:
>
> >I'm confused - if you can elaboratem that would be wonderful.
>
> quotation you cited doesn't sound very knowledgeable.
>
> If you doubt that ketosis is the natural state of human metabolism, go
> out into a wilderness area, and make a note of *all* the high-carb
> food that you can find and gather using only your hands, a rock, or a
> pointy stick (it be be a short list, and all of the items will be
> highly seasonal). That's how humans lived for neary a million years.
In east Africa where Homo sapiens evolved, tubers were likely eaten. Today,
there are 40,000 kilograms of tubers per square kilometer in Tanzania's
savanna woodlands, for example (Wrangham et al). A pointy stick would indeed
be all you would need. I doubt that early humans were unaware of, or unable
to utilise this resource.
In the Middle East, wild einkorn wheats can be harvested at the rate of 2.4
kilograms/hour -- a considerable resource (Gepts). Again, I doubt this
source of carbohydrate was not eaten well before the beginning of
agriculture 10,000 years ago.
Paul R
Paul Rogers
> "Paul Rogers" <ecol...@bigpond.net.au> wrote:
>
> >Probably occurs in endurance exercisers, eg, marathon runners when all
else
> >is gone! Under normal conditions of daily nutrition though I would expect
a
> >liver dump of stored glucose to be sufficient to prevent ketosis between
> >meals or overnight. Could be wrong though. Depends on how much you eat
and
> >burn.
>
> those who are gaining weight, specifically in the form of bodyfat.
> Ketosis is the normal way that the body has for metabolizing fat.
The production of ketone bodies (ketosis) in the liver does not mean they
are being burned for fuel. The liver does produce some ketone bodies as a
matter of normal metabolism. The upregulation and use as fuel depends on
carbohydate utilisation.
> Ketosis is commonly confused with ketonuria. Ketonuria is neither
> necessary nor sufficient for weight (fat) loss; ketosis is necessary
> (but not sufficient).
>
> Glycogen is a very short-term fuel. Endurance exercise requires
> burning of ketones or FFAs. Even mild aerobic exercise slightly
> suppresses gluconeogenesis, shifting the body toward "fat-burning"
> mode.
By prior carbohydrate loading, endurance exercisers hope to make glycogen in
liver and muscle last for some time. A meal two hours prior to exercise also
supplies circulating blood glucose which is used with FFAs in low-intensity
exercise. As time goes by in an endurance event the body will 'eat itself'
if it has to to keep going (at least if feels like it ;-), using all
available fuel sources, including ketones, in a desperate attempt to
maintain some glucose for brain function. Alas, this does not always occur
and the consequences are obvious.
Paul R
bert hubert
> bert hubert wrote:
>
>> I understand that normally protein is not a major contribution to
>> your caloric needs, however.
>
> This is not correct. With a few exceptions, you must burn an amount of
> protein equal to the amount you eat (absorb, actually). If you didn't,
> where else would it go?
I mean in the sense that it does not directly provide a large amount of
your daily energy needs on its own. In the absence of nuclear transmutation,
proteins are needed of course :-) The figure cited is around 10 to 15%
directly.
>> I get the impression from responses that
>> gluconeogenesis ... does occur in healthy people who are losing weight.
>
> No, this is not correct either. Most amino acids are "glucogenic." Their
> normal dispostion is to be converted to carbohydrate-like compounds
> (gluconeogenesis) and burned as carbohydrates would be. Some amino acids
> are "ketogenic" and are converted to ketones before being burned.
Does this correspond to what I said? 'Gluconeogenesis does occur in healthy
people who are losing weight' does not mention proteins.
Leucine and Lysine cannot act as precursors in gluconeogenesis, but the rest
can indeed take part.
Aren't proteins also used for non-burning needs?
Regards,
bert
bert hubert
<877B993D3BBEC459.4FDAE7F8...@lp.airnews.net>, Howard
Lee Harkness wrote:
> bert hubert <a...@ds9a.nl> wrote:
>
>>I'm confused - if you can elaboratem that would be wonderful.
>
> You might try reading _The Ketogenic Diet_ by Lyle McDonald. The
> quotation you cited doesn't sound very knowledgeable.
I have a hard time separating fact from fiction, sadly. McDonald is above a
lot of the diet books in stating that is not a quick & easy diet book, yet I
try to concentrate on books without 'diet' in the title.
The quotation I cite comes from a book with tons of references, so if needed
I can check their statements with other authors. Demarcation of science and
non-science isn't easy.
> If you doubt that ketosis is the natural state of human metabolism, go
> out into a wilderness area, and make a note of *all* the high-carb
> food that you can find and gather using only your hands, a rock, or a
> pointy stick (it be be a short list, and all of the items will be
> highly seasonal). That's how humans lived for neary a million years.
I'm not actually out in the wild that much and I rarely hunt & gather for my
food. Your argument about high-carb foods also misses the mark. I don't see
how a non-high-carb diet forces ketosis.
Unless quite a large revolution in our understanding of human metabolism has
occured, I think you are wrong. Ketosis appears to be the accumulation of
ketose bodies in the bloodstream - not just the usage of ketones!
Regards,
bert
bert hubert
<32D0C5F7F958FC9F.70C0C4B6...@lp.airnews.net>, Howard
Lee Harkness wrote:
> If you are not in ketosis, the brain does use about 100g/day of
> glucose, but if you are in ketosis for a while, about half of the
> brain's energy is derived from ketones, all of which can be supplied
> by the liver's conversion of protein. This is the natural state of
Fatty acids are involved too, aren't they?
> human metabolism. In nature, sugar is only a short-term, emergency
> fuel.
You appear to be on some kind of holy war regarding carbohydrates! How would
a human in nature benefit from reeking of Acetone? There is also a lot of
evidence that the brain does not like running on ketones, as evidenced by
its reticense to use them when glucose is available.
Regards,
bert hubert
Jay Tanzman
bert hubert wrote:
>
> In article <3C39F039...@sph.llu.edu>, Jay Tanzman wrote:
> > bert hubert wrote:
> >
> >> I understand that normally protein is not a major contribution to
> >> your caloric needs, however.
> >
> > This is not correct. With a few exceptions, you must burn an amount of
> > protein equal to the amount you eat (absorb, actually). If you didn't,
> > where else would it go?
>
> I mean in the sense that it does not directly provide a large amount of
> your daily energy needs on its own. In the absence of nuclear transmutation,
> proteins are needed of course :-) The figure cited is around 10 to 15%
> directly.
Protein directly contributes 10 to 15% of energy needs because most of eat diets that are 10 to 15%
protein (by calories). Assuming your diet is not protein-deficient, however much protein your diet
contains is the amount of protein that you will burn for energy. This is explained in greater
detail below.
> >> I get the impression from responses that
> >> gluconeogenesis ... does occur in healthy people who are losing weight.
> >
> > No, this is not correct either. Most amino acids are "glucogenic." Their
> > normal dispostion is to be converted to carbohydrate-like compounds
> > (gluconeogenesis) and burned as carbohydrates would be. Some amino acids
> > are "ketogenic" and are converted to ketones before being burned.
>
> Does this correspond to what I said? 'Gluconeogenesis does occur in healthy
> people who are losing weight' does not mention proteins.
Sorry, what I wrote above was wrong. Breakdown of glucogenic amino acids is not the same as
gluconeogenesis. Gluconeogenesis is the synthesis of glucose from non-carbohydrate precursors.
Amino acids are mostly deaminated and burned for energy without first being converted to glucose. I
do not have a direct answer for your question as to whether gluconeogenesis is a significant source
of energy in healthy, weight-maintaining adults. My guess is that it is not. I have one
biochemistry text that states that in the first 24 hours of fasting that gluconeogenesis accounts
for 64% of glucose, but most of only fast for 12 consecutive hours a night, and another textbook I
have states that we our liver glycogen is only 50% depleted after a 12-hour fast.
> Leucine and Lysine cannot act as precursors in gluconeogenesis, but the rest
> can indeed take part.
>
> Aren't proteins also used for non-burning needs?
Ok, I think I see now what is confusing you. The only reason a healthy, non-body-builder,
non-pregnant adult needs to eat any protein at all, is because we are constantly breaking down the
protein of our tissues and enzymes. These catabolized proteins are burned for energy, and need to
be replaced by protein from our diets. We need on the order of 50 g/day of protein to accomplish
this. If we eat too little protein, we will be in negative protein balance, and will experience a
net loss of muscle mass. However, unless we are growing, recovering from disease or injury, are
bodybuilding, or are pregnant, we cannot be in positive protein balance; excess dietary protein will
be burned for energy. In essence, we will burn an amount of calories from protein equivalent to the
amount we eat, although the specific amino acid molecules we burn today will not all come from the
food we eat today; some will come from structural and functional body proteins that we've broken
down. Maybe a diagram will help to clarify things:
Breakdown of Replacement of
body protein -\ Amino ---> body protein
|--> Acid
Dietary | Pool ---> Burned for energy
protein ------/ (gluconeogenesis
mainly)
Assuming the diet is protein-deficient, replacement of body protein will equal breakdown of body
protein; therefore, the amount of protein burned for energy must equal the amount of protein in the
diet. That is, protein metabolism is in steady state.
-Jay
Cycomiko
Howard Lee Harkness <hark...@suespammers.org> wrote:
>"Paul Rogers" <ecol...@bigpond.net.au> wrote:
>
>>By prior carbohydrate loading, endurance exercisers hope to make glycogen
in
>>liver and muscle last for some time.
>
>simply eating more fat to improve athletic performance.
>
>--
>Howard H.
>http://home.attbi.com/~stowawayholster
Do your research, high fat diets for atheletes dont really help performance,
they dont hinder (as long as the althele is adapted) but dont improve.
Cycomiko
To email remove 'eatmespammingcunts'
DRCEEPHD
>From: Howard Lee Harkness hark...@suespammers.org
>Date: 1/7/02 10:48 PM Central Standard Time
>Message-id:
><93FFBFCFD8D351AE.67D48FE6...@lp.airnews.net>
>
>"Paul Rogers" <ecol...@bigpond.net.au> wrote:
>
>>By prior carbohydrate loading, endurance exercisers hope to make glycogen in
>>liver and muscle last for some time.
>
>It has been demonstrated that carb-loading is less effective than
>simply eating more fat to improve athletic performance.
>
>--
>Howard H.
From Guyton’s textbook of medical physiology, eighth edition, chapter 84.
Page 941. "Therefore, endurance is greatly enhanced by a high carbohydrate
dietary."
Endurance of marathon type athletes:
High carbohydrate diet 240 minutes
Mixed diet 120 minutes
High fat diet 85 minutes.
Page 944. Graph of replenished glycogen stores following 2 hours of exercise.
At the 10 hour point, the amount of replenished glycogen in mg/kg was:
High carbohydrate diet 16
No food approx. 3.8
Fat and protein diet approx. 3.5
Can’t agree with your statement.
Cee.
Martin E. Lewitt
bert hubert <a...@ds9a.nl> wrote:
>In article
><32D0C5F7F958FC9F.70C0C4B6...@lp.airnews.net>, Howard
>Lee Harkness wrote:
>
>> If you are not in ketosis, the brain does use about 100g/day of
>> glucose, but if you are in ketosis for a while, about half of the
>> brain's energy is derived from ketones, all of which can be supplied
>> by the liver's conversion of protein. This is the natural state of
>Fatty acids are involved too, aren't they?
No, fatty acids are not a significant source of energy for the brain.
They have difficulty crossing the blood-brain barrier.
>> human metabolism. In nature, sugar is only a short-term, emergency
>> fuel.
>You appear to be on some kind of holy war regarding carbohydrates! How would
>a human in nature benefit from reeking of Acetone? There is also a lot of
>evidence that the brain does not like running on ketones, as evidenced by
>its reticense to use them when glucose is available.
When ketones are in short supply, the brain reserves them for lipid
synthesis. When their levels have been elevated for two or three
days, ketone burning turns on in the brain. In other tissues, ketones
are burned preferentially to glucose, in tissue with mitochondria
and plenty of oxygen.
The brain retains an obligate need for glucose because the elongated
length of neurons gives them a high surface to volume ratio, and
the this surface, the cell membrane is metabolically active. Even
with a high number of mitochondria per unit volume, much of the
neuron length is going to be too far from mitochondria and is
going to need to rely on anerobic glycolysis for energy.
So, the reality is that the brain, like other tissues with
mitochondria is reticent to use glucose when ketones
are available in high enough concentration. The brain,
because of neuronal geometry retains an important residual need
for glucose. Unlike other tissues with mitochondria, the brain
delays ketone burning until higher concentrations have been
sustained for a couple of days. -- Martin
--
Personal, not work info: Martin E. Lewitt My opinions are
Domain: lew...@swcp.com P.O. Box 729 my own, not my
Hm phone: (505) 281-3248 Sandia Park, NM 87047-0729 employer's.
bert hubert
>>> brain's energy is derived from ketones, all of which can be supplied
>>> by the liver's conversion of protein. This is the natural state of
>
>>Fatty acids are involved too, aren't they?
>
> No, fatty acids are not a significant source of energy for the brain.
> They have difficulty crossing the blood-brain barrier.
I meant the creation of ketones - my chemistry background is too lacking to
know if Acetyl CoA is a protein. I have a lot of catching up to do.
> So, the reality is that the brain, like other tissues with
> mitochondria is reticent to use glucose when ketones
> are available in high enough concentration. The brain,
> because of neuronal geometry retains an important residual need
> for glucose. Unlike other tissues with mitochondria, the brain
> delays ketone burning until higher concentrations have been
> sustained for a couple of days. -- Martin
Thank you - this helps a lot in understanding how the brain burns energy.
Regards,
bert
John De Hoog
> So, the reality is that the brain, like other tissues with
> mitochondria is reticent to use glucose when ketones
> are available in high enough concentration.
Martin, it's good to see you here again. Someone, though, has to point out
to you and Bert that you are both using "reticent" in a very strange way. Is
"reluctant" perhaps the word you were searching for?
--
John De Hoog, Tokyo
Alex Brands
> >From: Howard Lee Harkness hark...@suespammers.org
> >It has been demonstrated that carb-loading is less effective than
> >simply eating more fat to improve athletic performance.
>
> From Guyton’s textbook of medical physiology, eighth edition, chapter 84.
>
> Page 944. Graph of replenished glycogen stores following 2 hours of exercise.
>
> At the 10 hour point, the amount of replenished glycogen in mg/kg was:
>
> High carbohydrate diet 16
> No food approx. 3.8
> Fat and protein diet approx. 3.5
The rate of glycogen replacement and improved athletic performance are two
different things.
Alex Brands
>
> BTW, for a significant portion of the population, diary products are
> more of a health hazard than smoking,
What's the problem with dairy?
Alex Brands
> Alex Brands <abbr...@artsci.wustl.edu> wrote:
>
> >What's the problem with dairy?
>
> Some folks are intolerant to lactose, others to casein (there is some
> overlap in the two groups).
In a previous post, you wrote:
"BTW, for a significant portion of the population, diary products are
more of a health hazard than smoking"
A lactose intolerance is hardly comparable to the dangers of smoking, and
the problems are easily avoided by:
-using lactose reduced milk
-using lactase pills
-avoiding milk and consuming fermented dairy products such as yogurt and
kefir
By casein intolerance, do you mean an allergy to casein? What are the
dangers of this that are comparable to the dangers of smoking?
Alex
MattLB
> > out into a wilderness area, and make a note of *all* the high-carb
> > food that you can find and gather using only your hands, a rock, or a
> > pointy stick (it be be a short list, and all of the items will be
> > highly seasonal). That's how humans lived for neary a million years.
>
> I'm not actually out in the wild that much and I rarely hunt & gather for my
> food. Your argument about high-carb foods also misses the mark. I don't see
> how a non-high-carb diet forces ketosis.
The point is, the body is set up such that most of it can run on fat
and only selected tissues (predominantly brain, muscles and red blood
cells) need/prefer to run on glucose. Blood glucose levels are
controlled such that glucose is only "allowed" to enter most cells
when blood concentrations exceed a certain level (a level commensurate
with the demands of the brain). This ensures that the brain always has
access to glucose, at the expense of other tissues - which can just
use fat instead.
With modern diets there is so much carbohydrate that blood levels
frequently exceed the threshold for insulin release and therefore
almost all cells can utilise glucose. The result is that any
accompanying dietary fat instead of being metabolized, is just stored
(with obvious results).
The more the intake of carbs is reduced, the more non-carb sources
will be used to provide energy. The way the body is set up, this means
fat stores are raided for fatty acids. As fatty acid levels rise in
the liver, more and more ketone bodies are produced. These diffuse out
of the liver into the bloodstream and thence round the body. Under
normal conditions the ketone bodies are removed from the blood and
metabolized as quickly as they diffuse out of the liver. Blood (and
urine) levels of ketone bodies are therefore very low, even though
they may be a significant fuel source (e.g. heart muscle and the
cortical kidney cells).
> Unless quite a large revolution in our understanding of human metabolism has
> occured, I think you are wrong. Ketosis appears to be the accumulation of
> ketose bodies in the bloodstream - not just the usage of ketones!
I would agree with this. Ketosis, is really a big (abnormal) increase
in blood ketone bodies, indicative of a failure of the liver to deal
with an increase in fatty acids, either because the ratio of fat:carb
in the diet is very high, or because starvation-induced
gluconeogenesis has removed too much of the oxaloacetate (to make
glucose for the brain) required to metabolize the fatty acids. The
result is more ketone bodies than can be dealt with quickly by the
tissues and thus a sustained, elevated blood concentration.
MattLB
Martin E. Lewitt
Yes, reluctant is about the third meaning on the list in the definition of reticent,
and is the one I had in mind for these reticent brain mitochondria. 8-)
Even the scientific literature has trouble avoiding anthropomorphizing language,
it usually uses "preference". Both fatty acids and ketones are "preferred"
fuels for mitochondria throughout the body, so that when they are high
enough glucose is conserved. The brain mitochondria behave the same way,
but only high ketone levels have been sustained for a couple of days.
Otherwise it seems more "concerned" with conserving ketones for lipid
synthesis than with conserving glucose. Glucose levels in the brain
are maintained at normal levels even during starvation, so the
residual anerobic needs for it are VERY important. Ketones are
the natural "signal" that it should switch its metabolism because
intake of carbs or perhaps all nutrients is low. Beyond their
role in lipid synthesiss, ketones are the bodies mans of making
fat energy available in water soluable form.
Ketones are brain food for lipid synthesis and in times
of need, energy. -- Martin
Martin Banschbach PhD
> your caloric needs, however. I get the impression from responses that
> gluconeogenesis (I still wonder why it is 'neo' - any genesis looks like
> 'new' to me) does occur in healthy people who are losing weight.
>
> I read elsewhere that the brain requires in the order of 100 grams of
> glucose/day, which combined with other glucose needs may well mean that
even
> when well fed, extra glucose is needed to keep everything running (or so I
> speculate as an amateur).
>
> Regards,
>
> bert
Bert, as an amateur, you have a pretty good feel for the discourse that has
occurred in this thread on gluconeogenesis.
Brain does indeed need glucose and your recollection of 100 grams per day is
pretty close to the actual requirement.
Glucose is actually essential in humans and an RDA has been set of 50 grams
per day. By essential, we are talking about a nutrient that may or may not
be synthesized in the human body but is still needed in the diet to allow
for normal metabolism.
We also have an RDA for choline which can also be synthesized in the human
body. The 50 grams of glucose is the minimum amount needed to spare protein
from excessive gluconeogenesis. By excessive gluconeogenesis, I mean a
negative nitrogen balance.
Brain needs 80 grams of glucose per day. With 50 grams of glucose coming in
each day, the remaining 30 grams is made up for by gluconeogenesis. During
starvation, the brain use of glucose will drop to about 40 grams per day and
it can't go any lower than this without severely affecting the ability of
the brain to get energy. The energy that would have come from the other 40
grams of glucose is provided by ketone bodies. All of the glucose to keep
the brain going during starvation is coming from gluconeogenesis.
Now, when does gluconeogenesis start? It starts as soon as the blood
glucose level returns to normal after a meal. Blood glucose levels will
peak within 1 hour after a meal and return to normal levels within 2 hours
after a meal in normal (non-diabetic) people. Amino acids from the meal are
being converted to glucose in the liver (this is called gluconeogenesis),
not to keep the blood glucose at a normal level but simply to get rid of
excess amino acids.
If the meal contained little or no protein, then gluconeogenesis would not
start until the liver ran out of glycogen. The liver will use it's glycogen
to keep blood glucose levels in the normal range to let the brain gets it's
daily fix of 80 grams of glucose. If the liver runs out of glycogen,
signals are sent out to start breaking down muscle protein to give the amino
acids that will be needed to form glucose in the liver. Signals are also
sent out to make fat tissue give up it's fat so muscle and other tissues can
use fatty acids instead of glucose. This extra fatty acid coming into the
liver leads to ketone body formation to give the brain an alternative fuel
until food is found and put into the mouth to give the brain it's fix of
dietary glucose.
It's that simple, both gluconeogenesis and ketogenesis are completely normal
and occur all of the time in normal healthy people who are eating on a
regular basis. When the liver is taking out un-needed amino acids after a
meal by converting them to glucose, it's also converting some amino acids to
ketone bodies.
--
Marty B. "You are what you eat."
Jay Tanzman
Martin Banschbach PhD wrote:
> Glucose is actually essential in humans and an RDA has been set of 50 grams
> per day.
Can you povide a citation for this please?
-Jay
Tecaddict
Martin Banschbach PhD
>
> > Glucose is actually essential in humans and an RDA has been set of 50
grams
> > per day.
>
>
> -Jay
Modern Nutrition in Health and Disease. Volume 1, page 40. "..the diet
should therefore provide about 50 grams of glucose/day. Thus, one can state
a minimum desirable intake of glucose but there does not appear to be an
ideal level of intake."
If you look at the 1989 RDA report you will also see this. That RDA report
also established for the first time a recommended intake for water. You
will not see glucose or water on a %Daily Value label even though both are
essential for humans. The truth is that many essential nutrients are not
required to be on product nutrient labels. The other truth is that most
essential nutrients are not going to cause death if they are not present in
the human diet.
Of all of the essential nutrients, a lack of water kills faster than any
other nutrient.
mark doran
news:a1fli4$cmu@boofura
> >
> >Martin, it's good to see you here again. Someone, though, has to point
out
> >to you and Bert that you are both using "reticent" in a very strange way.
Is
> >"reluctant" perhaps the word you were searching for?
>
> Yes, reluctant is about the third meaning on the list in the definition of
reticent,
> and is the one I had in mind for these reticent brain mitochondria. 8-)
Martin, would you mind please listing the other meanings you're thinking of?
And also the dictionary you have; I'd be interested to know. Kind of a hobby
of mine...
Thanks very much.
Mark D.
Jay Tanzman
Martin Banschbach PhD wrote:
>
> > Martin Banschbach PhD wrote:
> >
> > > Glucose is actually essential in humans and an RDA has been set of 50
> grams
> > > per day.
> >
> > Can you provide a citation for this please?
> >
> > -Jay
>
> Modern Nutrition in Health and Disease. Volume 1, page 40. "..the diet
> should therefore provide about 50 grams of glucose/day. Thus, one can state
> a minimum desirable intake of glucose but there does not appear to be an
> ideal level of intake."
"RDA" stands Recommended Dietary Allowance and none has been set for glucose or any carbohydrate.
The Food and Nutrition Board has a working group on macronutrients, but they have not reported out
yet. Furthermore, glucose is not considered essential. Your quote above is out of context. The
paragraph immediately preceding it concludes with this sentence: "Glucose is thus ruled out as an
essential nutrient in that the body is capable of limited gluconeogenesis."(1) The 50 g/day minimum
intake you quoted, as explained in the rest of the paragraph, is what is necessary to avoid ketosis
and can be equivalently obtained from glucose polymers. I agree that sufficient carbohydrate should
be consumed to avoid long-term ketosis because its consequences are unknown; however, glucose per se
is not an essential nutrient and no RDA has been set for it.
-Jay
Ref:
1. Shils et al (eds). Modern Nutrition in Health and Disease, 8ed (1994). Lea & Febiger: Malvern,
PA. Vol 1, p.40.
Alex Brands
> Undesired weight gain.
I've heard a lot of milk bashing, but I don't remeber hearing this one
before. Care to elaborate? How does casein cause undesired weight gain?
I assume you are talking about some effect that is in addition to the
calories it contains. Where did you learn about this?
Martin E. Lewitt
I was using dictionary.com, i.e., I didn't leave my chair in
this particular effort. 8-) -- Martin
Martin Banschbach PhD
> is not an essential nutrient and no RDA has been set for it.
>
> -Jay
There is a recommended intake for glucose (or a polymer of glucose such as
starch). RDA's have been replaced with RDI's and you are right, there is no
RDI or RDA for glucose. I should have said that there is a suggested daily
intake level for glucose which is 50 grams per day either as free glucose or
from the glucose polymer, starch.
Glucose is however, listed as an essential nutrient for humans. I was going
to insert the table where it is listed into my response but even in ASCII
format it would take (could not get the table to post). I will send you an
e-mail with the table attached.
It's a minor issue. The human body can get along quite nicely without a
daily fix of glucose. The term essential is in the process of being
re-defined. It used to mean not capable of being synthesized in humans and
needed to prevent pathological changes in human metabolism.
Now it's considered to be anything needed to maintain normal human
metabolism. If the body can synthesize it in amounts needed for normal
metabolism, then it's not an essential component of the human diet. If
enough can not be formed for normal metabolism, then some will have to be
present in the human diet, it will be essential to have it in the diet for
normal human metabolism.
Jay Tanzman
Martin Banschbach PhD wrote:
[snip]
> Glucose is however, listed as an essential nutrient for humans. I was going
> to insert the table where it is listed into my response but even in ASCII
> format it would take (could not get the table to post). I will send you an
> e-mail with the table attached.
Thanks. I tried to find it on the USDA's marginally navigable website, but couldn't.
> It's a minor issue. The human body can get along quite nicely without a
> daily fix of glucose. The term essential is in the process of being
> re-defined. It used to mean not capable of being synthesized in humans and
> needed to prevent pathological changes in human metabolism.
>
> Now it's considered to be anything needed to maintain normal human
> metabolism.
This is a logical change. It's about time.
-Jay
Alex Brands
> Now it's considered to be anything needed to maintain normal human
> metabolism. If the body can synthesize it in amounts needed for normal
> metabolism, then it's not an essential component of the human diet. If
> enough can not be formed for normal metabolism, then some will have to be
> present in the human diet, it will be essential to have it in the diet for
> normal human metabolism.
I'm sure this will open a can of worms about how normal ketosis is.