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Does an empty glycogen store force the body to use muscle protein as fuel?

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  • Does an empty glycogen store force the body to use muscle protein as fuel?

    "If adequate carbohydrate intakes are not maintained through a well balanced diet, then once any glycogen/carbohydrate stores have been used up, the body is forced into using protein in the form of muscle as fuel."

    I read this and wondered if any experts (or anyone, for that matter) could clarify this statement in a bit more detail please? The article basically said that if you want to lose fat you have to eat enough carbs. It's CW bullcrap but I want to know why it's wrong.

    Thank you!

  • #2
    I don't know if any protein muscle would be broken down during exercise, as the muscles would be burning fat as fuel once glycogen stores were depleted - but I doubt it. As long as an adequate high protein/carb refeed is done afterwards and calcium, magnesium and vitamin D levels were adequate, I expect the body would be able to repair any damage to muscle fibres incurred through the exercise. Otherwise there's risk of muscle loss through metabolism of damaged fibres post-exercise.

    I've heard that it's very painful when a marathon runner's glycogen stores run dry and they hit the wall because their muscles are then fuelled only by fat. Knowing this, I have no intention to empty my muscles' glycogen stores while I exercise.
    Last edited by paleo-bunny; 02-01-2012, 11:45 AM.
    F 5 ft 3. HW: 196 lbs. Primal SW (May 2011): 182 lbs (42% BF)... W June '12: 160 lbs (29% BF) (UK size 12, US size 8). GW: ~24% BF - have ditched the scales til I fit into a pair of UK size 10 bootcut jeans. Currently aligning towards 'The Perfect Health Diet' having swapped some fat for potatoes.

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    • #3
      It's true, except the part about the carbs. Depending on your activity level, most people could easily eat enough protein to meet their glucose needs. Some people cannot convert amino acids to glucose well enough to meet the demands so they need to eat more carbs. You'll know when this happens because you will feel like shit.

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      • #4
        Yes

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        • #5
          Depends. When it comes to heavy lifting, yes, because the demand you're placing on your body when lifting requires immediate energy that stored fat cannot accomodate for so muscle is used as fuel.

          That's the point of weight lifting, though, because once you stop and go on to recover (rest + eating), your body overcompensates during recovery which adds back more muscle to the 'used-as-fuel' area than was originally there.

          For low level activity that doesn't exert heavy stress on your body, I believe Mark has stated that your body bypasses glycogen stores completely and goes for stored fat exclusively.

          It makes sense, too, because glycogen is there for huge bursts of power.
          Last edited by Domino Theory; 02-01-2012, 02:12 PM.
          Fasting Evangelist - Embrace nothing, get everything.

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          • #6
            Nope.

            When glycogen is used up, and there is no carbs, fat is your source of fuel not muscle.

            If you really actually managed to deplete your glycogen entirely (pretty damn hard) and your body had no fat or couldnt metabolise fat fast enough you simply wouldnt be able to move your muscles.

            To the guy above, your body never "bypasses" glycogen, this is not true. Your muscles can only use glycogen (made from fat or carbs), or ATP from anaerobic respiration. and your also wrong about the body needing to use muscle for immeadiate energy, if the body cannot use glycogen fast enough the anaerobic system kicks in. Using protein for energy is never even considered. Sorry if this sounds patronising.

            The idea of muscle catabolism is never an issue, and only happens in extreme cases. Your body has the ability to preserve muscle through hormones (HGH etc.) for more than 48 hours, even when exercising. it is system which allowed hunter gatherers to fail to kill something one day, and still be able to use their muscles the next day. Even if you have 4% of fat on your body to spare do you realise how many calories that is?! work it out. And for further peace of mind, read up from Mr Berkham at Lean Gains. The expert on fasting, and muscle preservation/growth.
            www.beatingorthorexia.co.uk

            No more diets. No more stress. Health made easy. Living made incredible.

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            • #7
              I'm no expert, but I'd have to ask these few questions to guide this thread -

              Would the liver spend its glycogen in a rested, fasted state? I think no.

              Would the liver be able to synthesize new glycogen from ketones and starches in the diet? I think so.

              Could you really stay under sustained physical stresses long enough to deplete all your glycogen AND your anaerobic energy resources? It would take serious, voluntary, and suicidal effort - something like crossfit. For days on end. An empty glycogen store SHOULD turn on the fat furnace. From what little I understand.
              Crohn's, doing SCD

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              • #8
                Originally posted by Knifegill View Post
                I'm no expert, but I'd have to ask these few questions to guide this thread -

                Would the liver spend its glycogen in a rested, fasted state? I think no.
                Not an expert either, but when I fasted, even resting, I 'emptied' my glycogen stores and started using fat/ketones for energy.

                Would the liver be able to synthesize new glycogen from ketones and starches in the diet? I think so.
                Again, going by experience, when the glycogen is gone, only dietary carbs can be converted to replenish the stores and you stop making/using ketones.


                Could you really stay under sustained physical stresses long enough to deplete all your glycogen AND your anaerobic energy resources? It would take serious, voluntary, and suicidal effort - something like crossfit. For days on end. An empty glycogen store SHOULD turn on the fat furnace. From what little I understand.
                I have heard of world class marathon runners using ketone/fat power as their 'secret' weapon~ since they don't run out of fuel at the half way mark~

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                • #9
                  Originally posted by Domino Theory View Post
                  Depends. When it comes to heavy lifting, yes, because the demand you're placing on your body when lifting requires immediate energy that stored fat cannot accomodate for so muscle is used as fuel.

                  That's the point of weight lifting, though, because once you stop and go on to recover (rest + eating), your body overcompensates during recovery which adds back more muscle to the 'used-as-fuel' area than was originally there.

                  For low level activity that doesn't exert heavy stress on your body, I believe Mark has stated that your body bypasses glycogen stores completely and goes for stored fat exclusively.

                  It makes sense, too, because glycogen is there for huge bursts of power.
                  Serious lack of scientific understanding going on here.
                  F 5 ft 3. HW: 196 lbs. Primal SW (May 2011): 182 lbs (42% BF)... W June '12: 160 lbs (29% BF) (UK size 12, US size 8). GW: ~24% BF - have ditched the scales til I fit into a pair of UK size 10 bootcut jeans. Currently aligning towards 'The Perfect Health Diet' having swapped some fat for potatoes.

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                  • #10
                    Your body can only use protein for 15% of its energy at MAX (in normal healthy conditions). Usually its is far below 10%. Next, as long as a person consumes enough fats and proteins, the body can convert those into carbs through the process of gluconeogenesis in the liver and can make up to 200 grams of carbs a day through this. The liver can also convert a portion of lactic acid produced during exercise into carbs through the same process.
                    The process of converting protein into energy is extremely inefficient for the body and it will never be a large portion of the energy being expended unless you have depleted your other energy stores AKA starvation.

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                    • #11
                      More or less bullsh*t. That's not how your muscles work.

                      Your muscles are recruited in order based on fiber type. Type I fibers are recruited first and use primarily fat, type IIa fibers are recruited next and primarily burn glycogen and fat, and type IIx fibers primarily utilize glycogen. Now, if you are performing exercise at an intensity that activates all the way up to the type IIx fibers, once you run out of glycogen those muscles stop being recruited and performance drops significantly. They don't breakdown, they just fatigue and become incapable of contracting. It's not that there is so much damage to the fiber that it breaks down, it just stops contracting because they are out of fuel, kinda like a car that runs out of gas. If you enter a workout completely glycogen depleted, you just won't be capable of generating large amounts of force for more than 10 or so seconds because that's about what you get directly from ATP stores and creatine phosphate. Also, I find it hard to believe that this would be true considering they've done studies with 72 hour fasts that lead to no significant protein loss.

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                      • #12
                        Still googling~
                        Last edited by Nady; 02-01-2012, 06:07 PM.

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                        • #13
                          Originally posted by Chrish2891 View Post
                          The liver can also convert a portion of lactic acid produced during exercise into carbs through the same process.
                          The process of converting protein into energy is extremely inefficient for the body and it will never be a large portion of the energy being expended unless you have depleted your other energy stores AKA starvation.
                          The liver is not converting lactic acid into carbs as such - please refer to the Cori cycle. The lactic acid comes from glucose in the muscles in the first place. The liver cannot assist the muscles in providing extra ATP (the universal energy source) using the Cori cycle when glucose levels are low.

                          I agree that conversion of protein into glucose is undesirable as it compromises other much more useful liver functions. It's easy to lose fat and build muscle eating primally while preventing gluconeogenesis from precious protein.
                          F 5 ft 3. HW: 196 lbs. Primal SW (May 2011): 182 lbs (42% BF)... W June '12: 160 lbs (29% BF) (UK size 12, US size 8). GW: ~24% BF - have ditched the scales til I fit into a pair of UK size 10 bootcut jeans. Currently aligning towards 'The Perfect Health Diet' having swapped some fat for potatoes.

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                          • #14
                            Here's a review of low glycogen training:

                            Sports nutrition: the latest research into low glycogen training

                            It lists "increased muscle damage and breakdown, leading to potential losses in muscle mass" as a potential drawback, also "increased production of stress hormones leading to lowered post-exercise immunity".

                            Its general conclusion is that low glycogen training can be advantageous to endurance training but there's no evidence to suggest that it's advantageous to strength training and that it may even be harmful.
                            F 5 ft 3. HW: 196 lbs. Primal SW (May 2011): 182 lbs (42% BF)... W June '12: 160 lbs (29% BF) (UK size 12, US size 8). GW: ~24% BF - have ditched the scales til I fit into a pair of UK size 10 bootcut jeans. Currently aligning towards 'The Perfect Health Diet' having swapped some fat for potatoes.

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