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  1. #11
    gn's Avatar
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    aside from chemistry stuff, i keep wondering why would anyone want to replenish glycogen stores during a workout - isn't it exactly what one works out for, i.e. to exert oneself (=deplete glycogen stores)


    of course, if one is a professional athlete who gets paid for his/her performance that would make sense, but, to think of it, one doesn't work out just to work out and for the sake of working out, and refilling your "fuel tank" during excercise is useless and, i guess, counterproductive


  2. #12
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    Tarlach, that happens only in the liver or kidney.


    During a workout, it is true that you are undergoing gluconeogenesis and lipolysis at the same time. However, most of the fat you're burning is stored outside of the liver. During a workout, the majority of the glycerol formed from the breakdown of fat outside the liver doesn't enter gluconeogenesis. Instead it is taken up by muscle (or other) cells, converted to acetyl CoA, and finally enters the Krebs cycle.


    In animal models, even in a fasted (partial glycogen depleted) state the liver can only take up about 25% of the glycerol found in the bloodstream. The rest is utilized by other body tissues. Again in animal models, inhibition of lipolysis does not significantly change the rate of glycogen depletion. The conclusion that can be drawn from this is that the products of lipolysis are not major players in synthesis of glucose for glycogen repletion.


    I'll concede that it is biochemically possible. But let's talk about reality. The contribution of triglyceride metabolism to glycogen repletion is small compared to the others I listed (dietary carb, dietary protein, and protein catabolism).


    Fat -> glucose -> glycogen just isn't a significant part of our metabolism.


  3. #13
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    @Pikaia


    I don't agree that during workout most of the fat burnt is from the fat around the liver.


    I have seen on me that I lost my skin fat while I was just doing workouts but following eating less eating 6 times a day.


    I started to lose my abdominal fat only when I started low carb periods.


    I think during workouts fat around skin gets burnt, and at all times when insulin is low, fat around liver will go first.


    So the glycerol produced from fat breakdown will not convert to glucose, as it would need to get to the liver first.


    Also I understand that glycerol to glucose conversion is not very common, and cannot be relied upon. The only real option is protein (whether dietary or muscular) to glucose conversion.


  4. #14
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    Anand, I don't disagree with you. Maybe my wording was ambiguous. I wrote: "However, most of the fat you're burning is stored outside of the liver." By that I meant that it is NOT stored in/around the liver. It is distant to the liver, ie. subcutaneous fat or intramuscular fat.


    But if what Tarlach says is happening, it can only happen in the liver or kidney, because only the liver or kidney can make glucose out of glycerol. Since we know that the majority of glycerol liberated from triglycerides doesn't end up in the liver or kidney, there's no way for it to be converted to glucose. We agree on that, right?


  5. #15
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    I was thinking about this after visiting Charles Washington’s blog (http://blog.zeroinginonhealth.com/) and reading about his workout. He appears to have no problems whatsoever with rapidly-depleting/repleting glycogen stores.


    The need to replenish muscle glycogen stores through dietary carbs might very well blown out of proportion.

    “Every saint has a past and every sinner has a future.” -Oscar Wilde
    "The power of accurate observation is commonly called cynicism by those who have not got it." -George Bernard Shaw
    "The trouble with jogging is that the ice falls out of your glass." -Martin Mull

  6. #16
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  7. #17
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    He apparently doesn't, that's my point. I'm addressing the notion that runners need carbs in order to perform properly. He seems fine: http://blog.zeroinginonhealth.com/?page_id=427

    “Every saint has a past and every sinner has a future.” -Oscar Wilde
    "The power of accurate observation is commonly called cynicism by those who have not got it." -George Bernard Shaw
    "The trouble with jogging is that the ice falls out of your glass." -Martin Mull

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