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Thread: Gluconeogenesis - When is lean muscle protein consumed? page

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    Omni's Avatar
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    Gluconeogenesis - When is lean muscle protein consumed?

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    I began wondering about this and if we are supposed to be fat burners, then we should be equiped to generate enough glucose for essential functions during fasting without severly affecting lean muscle protein.
    I listened to an interview with Stephen Phinney where he mentioned during the lipolysis as fatty acids are released for metabolism, the glyceride molecule from the Trigs is then converted by the liver to glucose, so in full flight keto, I read this may provide around 15-20g of glucose, so this is say 20% of the 120g essential brain requirement.
    I also think Pklop mentioned in the fasting thread that during a fast the body scavanges waste protein remnants around the body for Gluconeogenesis as well, but I haven't seen a figure for quantity. I think he also mentioned from his studies that it is only after about 50 hours of fasting that loss of lean muscle tissue becomes an issue.

    So can we assume then that during fasting/ketosis there is an ongoing requirement of around 100g of glucose per day, which at 60% efficiency translates to about 160 - 180g of protein just for Gluconeogenesis and our intake would need to be greater than that to ensure normal body maintenance was carried out as well.

    The link below describes the Glyceride to glucose rate.
    Glycerol gluconeogenesis in fasting humans. [Nutrition. 1995 Mar-Apr] - PubMed - NCBI
    Glycerol gluconeogenesis in fasting humans.

    Baba H, Zhang XJ, Wolfe RR.

    Abstract

    The contribution of glycerol to glucose production has been measured in healthy volunteers by the simultaneous primed constant infusion of 1-[13C]glycerol and 3-[3H]glucose and the determination of the rates of appearance (Ra) of glycerol, glucose, and glycerol-derived glucose. In the postabsorptive state, glycerol Ra was 3.11 +/- 0.44 mumol.kg-1.min-1, of which 36% was converted to glucose, accounting for 4.5% of total glucose production. After 62-86 h of starvation, glycerol Ra rose to 5.32 +/- 0.58 mumol.kg-1.min-1, and 68% of glycerol was converted to glucose. This accounted for 21.6% of total glucose production. Glycerol Ra was closely correlated with its conversion and contribution to glucose. These findings confirm that the contribution of glycerol to glucose production is directly correlated to its release as a consequence of lipolysis and support the notion that the central physiological role of accelerated lipolysis in fasting is the provision of gluconeogenic precursor.

  2. #2
    Lewis's Avatar
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    Quote Originally Posted by Omni View Post
    So can we assume then that during fasting/ketosis there is an ongoing requirement of around 100g of glucose per day ...
    No, it's much less than that. In that state the brain, which unlike the muscles can't burn fatty acids, mostly runs on β-hydroxybutyrate.

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    Omni's Avatar
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    Thanks for the prompter,
    Just dug a bit deeper, this is from Wiki, would this be a fairly accurate description for a "Ideally Fat Adapted" individual?

    Starvation response - Wikipedia, the free encyclopedia
    After the glycogen reserve is used up, glucose can be obtained from the breakdown of fats. Fats from adipose tissue are broken down into glycerol and free fatty acids. Glycerol can then be used by the liver as a substrate for gluconeogenesis, to produce glucose.

    Fatty acids can be used directly as an energy source by most tissues in the body, except the brain, since fatty acids are unable to cross the blood–brain barrier. After the exhaustion of the glycogen reserve, and for the next 2–3 days, fatty acids are the principal metabolic fuel. At first, the brain continues to use glucose, because, if a non-brain tissue is using fatty acids as its metabolic fuel, the use of glucose in the same tissue is switched off. Thus, when fatty acids are being broken down for energy, all of the remaining glucose is made available for use by the brain.

    However, the brain requires about 120 g of glucose per day (equivalent to the sugar in 3 cans of soda), and at this rate the brain will quickly use up the body's remaining carbohydrate stores. However, the body has a "backup plan," which involves molecules known as ketone bodies. Ketone bodies are short-chain derivatives of fatty acids. These shorter molecules can cross the blood–brain barrier and can be used by the brain as an alternative metabolic fuel.

    After 2 or 3 days of fasting, the liver begins to synthesize ketone bodies from precursors obtained from fatty acid breakdown. The brain uses these ketone bodies as fuel, thus cutting its requirement for glucose. After fasting for 3 days, the brain gets 30% of its energy from ketone bodies. After 4 days, this goes up to 70%.

    Thus, the production of ketone bodies cuts the brain's glucose requirement from 120 g per day to about 30 g per day. Of the remaining 30 g requirement, 20 g per day can be produced by the liver from glycerol (itself a product of fat breakdown). But this still leaves a deficit of about 10 g of glucose per day that must be supplied from some other source. This other source will be the body's own proteins.

    After several days of fasting, all cells in the body begin to break down protein. This releases amino acids into the bloodstream, which can be converted into glucose by the liver. Since much of our muscle mass is protein, this phenomenon is responsible for the wasting away of muscle mass seen in starvation.

    However, the body is able to selectively decide which cells will break down protein and which will not. About 2–3 g of protein has to be broken down to synthesise 1 g of glucose; about 20–30 g of protein is broken down each day to make 10 g of glucose to keep the brain alive. However, this number may decrease the longer the fasting period is continued in order to conserve protein.
    So theoretically, using only 30g protein per day, one could survive for a week with no food and only lose about 200g of protein, Interesting!!

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    When do we consume lean muscle tissue? All the time. We just have to make sure we're replenishing it faster than we're consuming it.

    With fat, for most of us, we hope to consume it faster than we replenish it.

    We're natural fat burners. We're also natural sugar burners. We will always burn both. It just depends on the activity. The lower the heart rate, the higher the ratio of fat-to-sugar consumed. The higher the heart rate, the lower the ratio of fat-to-sugar we consume.

    The OP mentions ketosis. We don't naturally run on ketosis and it's a "back-up" metabolism. We can live off it just fine, but it's not ideal for 99% of us (there are rare cases where it may be medicinal like certain cancers or to control seizures). Comparing how the body functions in a mode that does not deliver ideal performance IMO is a logical fallacy.

    IMO, don't overthink this stuff. That's how broscience got started. A bunch of people started thinking it "made sense" to consume many small meals a day to "stoke the metabolic fires" and it became a rule. Then, they started thinking that working a muscle over and over again until you're sore and your body is on fire is more productive because you "feel the burn." Now we have a bunch of bros doing curls in squat racks and holding people up that want to do actual physical activity in the gym...like squats. Then, we started the aerobics revolution...I can't even begin to summarize how wrong that is in a sentence. Actual science doesn't support these things at all. Sometimes, what makes sense isn't what really happens.
    Last edited by ChocoTaco369; 09-04-2012 at 06:07 AM.
    Don't put your trust in anyone on this forum, including me. You are the key to your own success.

  5. #5
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    Quote Originally Posted by ChocoTaco369 View Post
    The OP mentions ketosis. We don't naturally run on ketosis and it's a "back-up" metabolism. We can live off it just fine, but it's not ideal for 99% of us (there are rare cases where it may be medicinal like certain cancers or to control seizures). Comparing how the body functions in a mode that does not deliver ideal performance IMO is a logical fallacy.

    IMO, don't overthink this stuff. That's how broscience got started. a sentence.
    Right. And tossing out a "99% of us" generalization isn't bro-sci?

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    ChocoTaco369's Avatar
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    Quote Originally Posted by Paleobird View Post
    Right. And tossing out a "99% of us" generalization isn't bro-sci?
    Nope. "99%" isn't a figure, it's a synonym for "overwhelming majority," just like "1%" is a synonym for "rare case." You fall into the "1%" for sure, but how many people have a similar condition? Surely <1% of the population - and that's a real figure. I don't believe that a backup metabolic state should be labeled as "ideal" aside from very rare exceptions, and you won't be changing my mind on that anytime soon. I'm not saying ketosis is unhealthy. I'm simply stating that it's not ideal for optimal performance.
    Don't put your trust in anyone on this forum, including me. You are the key to your own success.

  7. #7
    Paleobird's Avatar
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    Quote Originally Posted by ChocoTaco369 View Post
    Nope. "99%" isn't a figure, it's a synonym for "overwhelming majority," just like "1%" is a synonym for "rare case." You fall into the "1%" for sure, but how many people have a similar condition? Surely <1% of the population - and that's a real figure. I don't believe that a backup metabolic state should be labeled as "ideal" aside from very rare exceptions, and you won't be changing my mind on that anytime soon. I'm not saying ketosis is unhealthy. I'm simply stating that it's not ideal for optimal performance.
    You don't have to have epilepsy to benefit from ketosis and you won't be changing a lot of people's minds about that. At a minimum 89% of this board. See, I can make up statistics too.
    Last edited by Paleobird; 09-04-2012 at 04:03 PM.

  8. #8
    Omni's Avatar
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    How about some useful information?
    I'd like to know what the stages are in the transition from glycosis to ketosis, there must be a series of trigger points as the body switches over from one to the other.

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