Carbs for Glycogen stores - necessary or not?

[Fred]

I'm a little confused by this. My understanding was always that for anaerobic activity such as sprinting, I need to use my glycogen stores, and once they 'run out' then I will move into fat-burning mode and my performance would suffer.

So, if I were to go on a zero carb diet for say 3 months and perform sprints 4/5 times a week throughout, how would my performance go? Would my body adapt?

Theoretically, my logical conclusion would be that my glycogen stores would simply deplete further over time and therefore my performance would decrease. I'm not stupid enough to believe the human body is this simplistic however....

Anyone care to enlighten me?

[Weaves]

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I'm a little confused by this. My understanding was always that for anaerobic activity such as sprinting, I need to use my glycogen stores, and once they 'run out' then I will move into fat-burning mode and my performance would suffer.

So, if I were to go on a zero carb diet for say 3 months and perform sprints 4/5 times a week throughout, how would my performance go? Would my body adapt?

Theoretically, my logical conclusion would be that my glycogen stores would simply deplete further over time and therefore my performance would decrease. I'm not stupid enough to believe the human body is this simplistic however....

Anyone care to enlighten me?

Of course your body would adapt

[Fred]

Yes, I realise it will adapt, but to what extent?

[Was_once_fat_dave]

Very hot topic mate, you'll get ATZ and Nu going again on this one.

It's argued to death in this thread http://forum.myprotein.co.uk/advance...repletion.html Lots of very good info on both sides of the story.

Regards the sprints, although he doesnt recomend a zero carb diet, Mark Sissons over at Marks Daily Apple, recomends a low carb lifestyle (sub 150g and then only from veggies and the occasional fruit) AND sprinting.

[CosmicFish]

Anecdotally, I'm on a VLCD and have been since 1st Jan (CHO intake is averaging 38g/day). Compliance has been ~97% (I've had one planned cheat in Jan and one in Feb so far). Strength is down - I attribute that to having lost ~18lbs so far and the calipers tell me that I'm losing 25% of it as lean tissue. Endurance is slightly down, but nowhere near as much as I'd originally expected, so somehow my body seems to be keeping glycogen mostly topped up.

Best bet, IMO, try it and see. And keep detailed notes and records.

[Fred]

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Very hot topic mate, you'll get ATZ and Nu going again on this one.

It's argued to death in this thread http://forum.myprotein.co.uk/advance...repletion.html Lots of very good info on both sides of the story.

Regards the sprints, although he doesnt recomend a zero carb diet, Mark Sissons over at Marks Daily Apple, recomends a low carb lifestyle (sub 150g and then only from veggies and the occasional fruit) AND sprinting.

Wow!! 51 pages of debate in there!!

I have to say, it is of great interest to me. How do we know at which point glycogen depletion has been reached. there seem to be so many unanswered questions within this.

[ATZ]

You can't. Muscle may feel "flat" you'll feel pretty rubbish attempting to lift etc.

[Verth]

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I have to say, it is of great interest to me. How do we know at which point glycogen depletion has been reached. there seem to be so many unanswered questions within this.

Just under 2 hours into a marathon in my expeience lol - After that it's all pain

Your muscles just 'die' and suddenly (though after a lot of training it's not that sudden) become 'heavy' - They gradually get less heavy as you move into fat burning mode - Top marathoners of course have finished the marathon by this point - One of the advantages of being fast.

Not sure you'd ever reach that point 'sprinting'. Normally your barrier in sprinting is lactic buffering.

[NU_nutrition_TS]

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I'm a little confused by this. My understanding was always that for anaerobic activity such as sprinting, I need to use my glycogen stores, and once they 'run out' then I will move into fat-burning mode and my performance would suffer.

So, if I were to go on a zero carb diet for say 3 months and perform sprints 4/5 times a week throughout, how would my performance go? Would my body adapt?

Theoretically, my logical conclusion would be that my glycogen stores would simply deplete further over time and therefore my performance would decrease. I'm not stupid enough to believe the human body is this simplistic however....

Anyone care to enlighten me?

First of all it is virtually impossible to eat a diet with zero carbs (I can get as low as about 5g per day). Secondly, eating little to no carbs does not mean you do not have glucose in your blood (and hence the ability to convert that to glycogen in either liver or muscles).

This is patently the case because, even on my minimal carb diet, I have normal blood glucose levels. Even when I fast for prolonged periods, my blood sugar rarely drops to hypoglycaemic levels, so I must be keeping my liver glycogen sufficiently topped up to keep blood glucose levels stable during long periods without food.

Absolutely muscle glycogen will get the short end of the stick but whether you will be so depleted that you cannot perform any physical work is also unlikely unless you severely limit food intake and indulge in long and frequent intense physical activity.

Liver and muscle glycogen are synthesised from glucose and the body will always have glucose even without much in the way of dietary carbs as long as you eat plenty of fat and protein to provide the substrate for gluconeogenesis.

Again, I am not saying you will have the same levels of muscle glycogen as someone on a high carb diet, but it won't be totally depleted either if you are providing sufficient recovery time (24-48 hours between intense physical exertion). So your carb intake has to be dictated by the intensity and frequency of your activity.

[ATZ]

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So your carb intake has to be dictated by the intensity and frequency of your activity.

That's one of THE most sensible things I've heard you say on the topic in ages!