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But the point is that protein and fats are always supplied, so technically you can't say that someone is starving on that diet.
And all the glucose that is needed is being manufactured from the labile amino acid pool, with the excess going into glycogen.
So why is this a bad thing?
And most foods are not straight protein, fats, or carbs. There is a little mix of all three in almost all commonly ingested foods, to a greater or lesser degree.
But the point is that protein and fats are always supplied, so technically you can't say that someone is starving on that diet.
My point isn't that the person would be starving, but instead that the mechanisms that allow one to subsist on fats and proteins are those used during starvation. All mammals, even those that eat very little fats as part of their diet, can subsist on fats and protein because its how they survive when food isn't available. But just because we can do something, doesn't mean its optimal to do it.
Quote:
Originally Posted by steve035
And all the glucose that is needed is being manufactured from the labile amino acid pool, with the excess going into glycogen.
Humans don't synthesis much glucose from protein, just enough to keep some glucose dependent cells running, so this mechanism isn't a replacement for dietary carbohydrates.
All brain cells run on glucose- and there are 100 billion of them. So an adequate supply is essential.
Gluconeogenisis IS a replacement for ingesting carbs. As much glucose as is needed is manufactured.
What does the cell care if six-carbon glucose molecule comes from the breakdown of carbs or made from amino acids?
But I would like to see your source for these finer points of metabolism.
I use Guyton's, but I don't recall it specifically addressing the replacement of glycogen when the glucose base units are supplied through gluconeogenisis.
All brain cells run on glucose- and there are 100 billion of them. So an adequate supply is essential.
Not all brain cells are glucose dependent, only a fraction of them are, the rest can metabolize fats. So only a relatively small amount of glucose is required to prevent death.
Quote:
Originally Posted by steve035
Gluconeogenisis IS a replacement for ingesting carbs. As much glucose as is needed is manufactured.
The body only *needs*, metabolically speaking, a relatively small amount of glucose to run....but just because the body can run primarily on fats (e.g., ketosis) doesn't mean this represents an optimal state for the body. All animals, regardless of diet type, can fuel themselves on a diet of protein and fats by utilizing the mechanisms they use during starvation. Does this mean all animals will thrive long-term of a diet of protein and fat? No, what the body can do when pushed is much different than what is optimal.
The human liver is limited in how much protein it can process, intakes higher 200 grams a day can result in problems and the maximal intake is believed to be around 280~300:
Your study is done by two people who have no professional credentials.
This is a cut and paste from the abstract:
"Dangers of excessive protein, defined as when protein constitutes > 35% of total energy intake, include hyperaminoacidemia, hyperammonemia, hyperinsulinemia nausea, diarrhea, and even death (the "rabbit starvation syndrome")."
This is a ridiculous statement. DEATH from eating more than 35% protein in your diet?
REALLY?!!!!
You'll have to cite studies done by medical professionals to convince me.
This is from Guyton's- the gold standard for medical physiology...
"When the body’s stores of carbohydrates decrease
below normal, moderate quantities of glucose can be
formed from amino acids and the glycerol portion of fat.
This process is called gluconeogenesis.
Gluconeogenesis is especially important in preventing
an excessive reduction in the blood glucose concentration
during fasting. Glucose is the primary substrate
for energy in tissues such as the brain and the red blood
cells, and adequate amounts of glucose must be present
in the blood for several hours between meals. The liver
plays a key role in maintaining blood glucose levels
during fasting by converting its stored glycogen to
glucose (glycogenolysis) and by synthesizing glucose,
mainly from lactate and amino acids (gluconeogenesis).
Approximately 25 per cent of the liver’s glucose production
during fasting is from gluconeogenesis, helping
to provide a steady supply of glucose to the brain.
During prolonged fasting, the kidneys also synthesize
considerable amounts of glucose from amino acids and
other precursors."
Every day the body shifts over to the "fat-burning" mode. It is part of the routine.
As far as the brain goes, it can only adapt to the use of ketone bodies (made from fatty breakdown products) after DAYS of frank starvation.
I would like to see a long-term prospective clinical study done on an exclusively fat/protein diet and long-term function.
Just because a study is in an NIH database, does not mean it is worth anything, or done by people medically qualified.
Your study is done by two people who have no professional credentials.
This is a cut and paste from the abstract:
"Dangers of excessive protein, defined as when protein constitutes > 35% of total energy intake, include hyperaminoacidemia, hyperammonemia, hyperinsulinemia nausea, diarrhea, and even death (the "rabbit starvation syndrome")."
This is a ridiculous statement. DEATH from eating more than 35% protein in your diet?
The authors are Ph.ds and you can find a number of studies (I'll cite more if you can't find them) on this, protein toxicity is often referred to as "rabbit starvation" because it was first observed when some people consumed a lot of rabbits (which are very lean, so its almost all protein).
What you're citing doesn't say anything about protein toxicity, its about routine protein metabolism.
Quote:
Originally Posted by steve035
Every day the body shifts over to the "fat-burning" mode. It is part of the routine.
"The body" doesn't act collectively, each cell type has different preferences and responses differently to what is being consumed. For example, many organs prefer to oxidize fats for energy, muscle runs on a mix unless active it prefers all glucose. Etc. But yeah, throughout the day the body is using a mix of fat and glucose, but that doesn't mean that forcing it to run primarily on fats due to carbohydrate restriction is a healthful practice.
Quote:
Originally Posted by steve035
As far as the brain goes, it can only adapt to the use of ketone bodies (made from fatty breakdown products) after DAYS of frank starvation.
The brain will start to use ketone bodies after the bodies glucose stores (glycogen) have been depleted, but the point is, the actual glucose *needs* (i.e., to prevent death) are relatively low. But preventing cell death.....and achieving optimal health are two different things.
I want to see real clinical studies to prove these things. Prospective.
What are their PhDs in? I did a little research and found them in some sports oriented company. Their credentials were not featured at all. What does that tell you? I want studies from medical doctors from respected institutions.
If you show me something in a recent edition of Guyton's, or even suggested by Guyton's, I will take it seriously.
But for the average person, these speculations are moot. Even in beef, five percent of the calories you ingest are going to be carbohydrates. And half of the remaining calories are going to be from fat, and not protein.
"But yeah, throughout the day the body is using a mix of fat and glucose, but that doesn't mean that forcing it to run primarily on fats due to carbohydrate restriction is a healthful practice."
Well, I defy you to show me someone who intentionally ate a low-carbohydrate diet to the point where bad things started to happen.
And, no, the brain will run on the glucose manufactured in the liver through the process of gluconeogenisis, which is released into the bloodstream. If the pool of labile amino acids is replenished, as it would be in a high-protein diet, glucose will be continued to be manufactured and the brain would use the glucose preferentially. Glycogen is just along for the ride, whatever level it settles out at in a super hi protein diet.
On an exclusively protein/fat diet (if that is possible to maintain for any length of time) I would think that the body would keep a baseline emergency store of glycogen- perhaps 30-40 percent of maximum capacity. I don't have any proof of that but it would make sense.
Of course, individual cells are impossible to monitor for switchover from glucose to fat metabolism. These are indirect measurements using carbon dioxide/oxygen respiration measurements over time in human subjects.
What are their PhDs in? I did a little research and found them in some sports oriented company. Their credentials were not featured at all. What does that tell you? I want studies from medical doctors from respected institutions.
Firstly medical doctors are not scientists, they are doctors, research is typically conducted by scientists. Not sure what you looked up, but both of the authors are professors at respected universities and have a number of published works. Here is Professor Neil Mann:
You'll notice that he is supportive of the whole "paleo diet" thing, not exactly someone that would exaggerate the dangers of excessive protein intake.
Guyton's and Hall's Textbook of medical physiology is a textbook used in medical schools, its not a textbook on biochemistry, I'm not sure why you keep mentioning it. It doesn't have any relevance to science.
Quote:
Originally Posted by steve035
And, no, the brain will run on the glucose manufactured in the liver through the process of gluconeogenisis, which is released into the bloodstream.
Do you have a citation for this? I'm not aware of any study that has looked at what happens in the brain when carbohydrates are restricted,but fat and protein intake is kept high. The body can convert protein into both carbohydrates and fat, so its by no means a given that the body will convert significant amounts of the protein into carbohydrates. I think its far more likely that a high protein/fat diet will induce ketosis and gluconogenesis will be fairly minimal, but again, I've love to see a study on this.
But, much of this is besides the point, I haven't disagreed with the fact that the body can survive with just dietary protein and fats.....what I have suggested is that being able to survive on such a a diet, something that any animal could do, says very little about whether a human would thrive long-term on such a diet.
Any serious medical researcher first goes to medical school to become a doctor, then specializes in whatever area they want to concentrate in and take an academic position at a medical school.
Your RMIT is an online vocational school.
I think that speaks for itself.
The Guyton and Hall textbook is the accepted world standard for the most up-to-date knowledge of human physiology we have. You can download an older edition for free.
That you RIDICULE this textbook is sad.
On the subject, this is an excerpt from chapter 68 of Guyton's. It indicates that it takes weeks for someone switching over from a normal to an mostly fat diet for the brain to begin to utilize ketone bodies for fuel. But the Eskimos live like this, with the brain depending a lot on ketones, without problems.
"Adaptation to a High-Fat Diet. When changing slowly from
a carbohydrate diet to an almost completely fat diet, a
person’s body adapts to use far more acetoacetic acid
than usual, and in this instance, ketosis normally does
not occur. For instance, the Inuit (Eskimos), who sometimes
live almost entirely on a fat diet, do not develop
ketosis. Undoubtedly, several factors, none of which is
clear, enhance the rate of acetoacetic acid metabolism
by the cells. After a few weeks, even the brain cells,
which normally derive almost all their energy from
glucose, can derive 50 to 75 per cent of their energy from
fats."
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