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weight and dehydration

neebneeb Posts: 4,448
edited September 2009 in Training, fitness and health
Is loss of 2-3kg the day after a long ride always due to dehydration? Is it possible to still be dehydrated even if your pee is clear? (Presumably your kidneys can only absorb a certain amount of water at a time, so if you drink a lot quickly will some of it pass straight through even if you are still dehydrated?)

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  • InfamousInfamous Posts: 1,130
    If you drink too much you can wash all the salt out of your body. Salt is what kidneys need to absorb the water.
  • neebneeb Posts: 4,448
    Would salt loss cause weight loss though? So can you still assume that you are dehydrated if you are 2-3kg under normal weight? But maybe you can be dehydrated and still drink too much too quickly, thus upsetting salt balance?

    It might sound weird but I sometimes find it difficult to know if I am drinking too much or too little, especially before and after a strenuous ride (obviously it is difficult to drink too much during the ride).
  • sampras38sampras38 Posts: 1,917
    neeb wrote:
    Would salt loss cause weight loss though? So can you still assume that you are dehydrated if you are 2-3kg under normal weight? But maybe you can be dehydrated and still drink too much too quickly, thus upsetting salt balance?

    It might sound weird but I sometimes find it difficult to know if I am drinking too much or too little, especially before and after a strenuous ride (obviously it is difficult to drink too much during the ride).

    if you're not sure, just aim for around 500ML of fluid per hour. If you do that you won't be far off.
  • jibberjimjibberjim Posts: 2,810
    neeb wrote:
    Is loss of 2-3kg the day after a long ride always due to dehydration? Is it possible to still be dehydrated even if your pee is clear? (Presumably your kidneys can only absorb a certain amount of water at a time, so if you drink a lot quickly will some of it pass straight through even if you are still dehydrated?)

    No, you burn energy too. Either fat, or glycogen. You have maybe 500g of glycogen available to you, which with the water that is used to store it will be 1.8kg, if you completely consumed all of that, you could be down 1.8kg and still have the same amount of water otherwise in your system.

    Don't try to replace all the weight lost by drinking.
    Jibbering Sports Stuff: http://jibbering.com/sports/
  • You won't have the same amount of water in your system if you are glycogen depleted as glycogen is stored with water. 6g to every 1g of glycogen I believe.

    Just drink until you are peeing nice and clear.
  • neebneeb Posts: 4,448
    Thanks all. I guess if in doubt about salts the best thing is just to drink gatorade...
  • jibberjimjibberjim Posts: 2,810
    neeb wrote:
    Thanks all. I guess if in doubt about salts the best thing is just to drink gatorade...

    Erm, not really, it doesn't make a whole lot of difference, see

    http://www.sportsscientists.com/2007/10 ... se_26.html

    and

    http://www.sportsscientists.com/search/ ... d%20intake
    Jibbering Sports Stuff: http://jibbering.com/sports/
  • neebneeb Posts: 4,448
    Quick google....

    This area seems to be a minefield, lots of conflicting opinions...

    I suppose with gatorade you at least are unlikely to get water intoxication by drinking too much water when you don't need to, because it will provide electrolytes as well as water. If the sportsscientists guy is right (I notice he sells lots of advertising on his site so may also have an indirect agenda...) then gatorade, because it has a higher salt content than sweat, will increase the osmotic potential from inside your cells to outside, thus pulling water out of the cells to dilute the extra salts in the bodily fluids. Strange though that you don't often hear of people becoming seriously dehydrated from drinking too much gatorade... (or do you?) and as the gatorade is providing significant quantities of electrolytes too, it would presumably be difficult to get water intoxication from drinking too much of it, even if it does increase thirst.

    Of course it would be better not to drink at all when you don't need to... I've always suspected myself that thirst is there for a reason.. :wink:

    If the problem with gatorade however is simply that the electrolyte levels are too high because they are set to the levels that are found in blood rather than the lower levels in sweat, wouldn't the obvious solution (excuse the pun) simply be to mix it up from the powder at a lower concentration?
  • neebneeb Posts: 4,448
    Looking back at these sportsscientist articles there seems to be a contradiction, or maybe I have misread the first article. I thought he was suggesting in the first article that gatorade had higher salt concentrations than sweat, and thus led to increased salt levels:
    The really interesting finding was that the water group maintained their sodium concentration (a surrogate for the total osmolality) just fine, while the Gatorade group actually increaesed its concentration.
    And yet in the other article he says:
    This occurs even though sports drinks contain some sodium because they still have much less when compared to the body fluids.
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