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A followup
May. 3rd, 2006 08:51 pmJust as an addendum to my post yesterday about people prosletising about the benefits of drinking idiotic quantitites of water: drinking pure water if you're truly dehydrated is actually not an efficient way of rehydrating yourself.
If you've studied biology and/or anatomy, you'll know that water is transported into the bloodstream from the small intestine by way of osmosis. If you have an increased concentration of sodium across the intestinal wall, water is pulled across into the bloodstream (and so reduces the relative sodium concentration). Once the sodium concentration is sufficiently lowered, osmosis slows down and eventually stops.
Ok, so, to get the water transport happening, you need to have sufficient quantities of sodium in your bloodstream for it to take place, otherwise it doesn't reach a high enough concentration to get the osmotic mechanism working optimally. Drinking a lightly saline solution encourages this to occur, where pure water may just pass straight through. However, you might then think that, logically, if you drink a heavy saline solution, it'd get things working gangbusters. Of course, in reality, this isn't the case - what actually happens is that the saline solution is too strong on the wrong side of the intestine, thus drawing water out of the bloodstream and causing diarrhoea (as well as many other nasties if you poison yourself with sufficent salt). So, you know, drinking seawater is never a good idea. This is different compared to administering saline intravenously - since it goes directly to the bloodstream, it raises the sodium concentration in the right place (as well as obviously raising your fluid levels over all).
So, how to encourage the sodium/water transport to work a bit more quickly when you don't have a drip? In the late 70s (which isn't that long ago), it was discovered that glucose will transport sodium ions across the intestinal barrier into the bloodstream, on a one for one basis. Glucose is automatically absorbed by the intestine, with no other encouragement needed, since it's fuel for everything. However, too much glucose causes the same problem as too much sodium - it draws sodium out of the bloodstream, thus raising the concentration on the wrong side of the small intestine.
So, there you have it. If you have glucose in your hydrating solution, it transports the same number of sodium ions across into the bloodstream. As the concentration of the sodium rises, it draws water across the intestine until the sodium concentration reaches the appropriate balance. In the meantime, the glucose is burned off as fuel. Other things needed, if you're really going to town, are bicarbonate/citrate to reduce blood acidity, and potassium. With potassium, alas, you can't cheat with its absorption the same way as sodium - it's a purely passive process. So you need to supplement it. Bananas are good.
Good hydrating solutions will provide all those things - the Oral Rehydration Salts developed by Unicef to treat endemic diahorrea contain 3.5g salt, 2.9g citrate, 1.5g potassium chloride and 20g glucose, added to a litre of clean water. A home recipe Unicef suggest is 1 litre of water, 1/4 tsp each salt and bicarb, and 2 tbl (40g - only half of sucrose is glucose) sugar or honey. A 1/2 c of orange juice is suggested for better flavour and potassium, (the carb in that much OJ - 10g fructose - interestingly has no effect whatsoever on sodium transport, thus you need to leave the same amount of sugar in your solution).
Commercial preparations like Gatorade have WAY too much sugar in them. It's better to eat complex carbs and preload if you're going to do strenuous exercise that burns fuel. I do use stuff like that occasionally, but I end up chucking about 2/3rds away and topping it up with plain water (or whatever brings the glucose equivalent down to 20g/l).
I'm really in lecture mode at the moment. I have another one brewing on sexual politics, but I'll wait for another day to burden you all. :-)
If you've studied biology and/or anatomy, you'll know that water is transported into the bloodstream from the small intestine by way of osmosis. If you have an increased concentration of sodium across the intestinal wall, water is pulled across into the bloodstream (and so reduces the relative sodium concentration). Once the sodium concentration is sufficiently lowered, osmosis slows down and eventually stops.
Ok, so, to get the water transport happening, you need to have sufficient quantities of sodium in your bloodstream for it to take place, otherwise it doesn't reach a high enough concentration to get the osmotic mechanism working optimally. Drinking a lightly saline solution encourages this to occur, where pure water may just pass straight through. However, you might then think that, logically, if you drink a heavy saline solution, it'd get things working gangbusters. Of course, in reality, this isn't the case - what actually happens is that the saline solution is too strong on the wrong side of the intestine, thus drawing water out of the bloodstream and causing diarrhoea (as well as many other nasties if you poison yourself with sufficent salt). So, you know, drinking seawater is never a good idea. This is different compared to administering saline intravenously - since it goes directly to the bloodstream, it raises the sodium concentration in the right place (as well as obviously raising your fluid levels over all).
So, how to encourage the sodium/water transport to work a bit more quickly when you don't have a drip? In the late 70s (which isn't that long ago), it was discovered that glucose will transport sodium ions across the intestinal barrier into the bloodstream, on a one for one basis. Glucose is automatically absorbed by the intestine, with no other encouragement needed, since it's fuel for everything. However, too much glucose causes the same problem as too much sodium - it draws sodium out of the bloodstream, thus raising the concentration on the wrong side of the small intestine.
So, there you have it. If you have glucose in your hydrating solution, it transports the same number of sodium ions across into the bloodstream. As the concentration of the sodium rises, it draws water across the intestine until the sodium concentration reaches the appropriate balance. In the meantime, the glucose is burned off as fuel. Other things needed, if you're really going to town, are bicarbonate/citrate to reduce blood acidity, and potassium. With potassium, alas, you can't cheat with its absorption the same way as sodium - it's a purely passive process. So you need to supplement it. Bananas are good.
Good hydrating solutions will provide all those things - the Oral Rehydration Salts developed by Unicef to treat endemic diahorrea contain 3.5g salt, 2.9g citrate, 1.5g potassium chloride and 20g glucose, added to a litre of clean water. A home recipe Unicef suggest is 1 litre of water, 1/4 tsp each salt and bicarb, and 2 tbl (40g - only half of sucrose is glucose) sugar or honey. A 1/2 c of orange juice is suggested for better flavour and potassium, (the carb in that much OJ - 10g fructose - interestingly has no effect whatsoever on sodium transport, thus you need to leave the same amount of sugar in your solution).
Commercial preparations like Gatorade have WAY too much sugar in them. It's better to eat complex carbs and preload if you're going to do strenuous exercise that burns fuel. I do use stuff like that occasionally, but I end up chucking about 2/3rds away and topping it up with plain water (or whatever brings the glucose equivalent down to 20g/l).
I'm really in lecture mode at the moment. I have another one brewing on sexual politics, but I'll wait for another day to burden you all. :-)
