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I have read on various places that exercising for a prolonged period of time with excessive water intake can be dangerous. It may lead to water intoxication (hyponatremia).

After some searches and a few more articles, it seems that:

  • When you hike (especially in hot weathers) you sweat a lot. When you sweat your body loose electrolyte (namely sodium potassium calcium... etc) and also a lot of water.

  • When you drink water, you replace the lost fluid, but NOT the salt/minerals. This means the fluid in your body is diluted and your body functions will be affected (confusion, lost of balance and death in severe cases).

Drinking less water is not an option because of the intense sweating when hiking for 9 hours or so under the hot sun.

An obvious choice was to replace water with sports drink like Gatorade.

Firstly, I don't like sports drink. Secondly, I want to know what is the exact thing my body lost with excessive sweating and needed to be put back into my body.

I am not a chemist/biologist, but from what I read, the term electrolyte is loosely used to refer to a group of minerals. Sodium, potassium, calcium and more.

  • If I drink salt water, will it help?

  • If I eat banana (very rich in potassium), will it help?

But then, I am only getting sodium and potassium. Hikers recommend bringing complex carbohydrates and eating them frequently to fuel muscles.

I don't think complex carbs like wheat biscuits provide minerals when digested. They give a steady supply of sugar when digested, but sugar and carbs have nothing to do with body electrolyte balance.

  • Eating complex carbohydrates will fuel your body, but it does nothing to restore the electrolyte balance in your body, is this correct?

I weight 105kg and I am 6'2 (189cm), I drank around 5 litres of water in a 7 to 9 hours day-hike. I had some biscuits and 3 bananas, and 1.2 out of the 5 litres of fluid I had was sports drink.

However by the end of the hike I was feeling a slight headache. Was it because I was drinking too much water?

I want to find out what the body looses with excessive sweating, and what are the ways to eat/drink accordingly to replenish the lost substances.

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Was this your first time hiking (especially so long)? –  Baarn Dec 24 '12 at 8:21
    
This answer has some information on energy drinks with a link to a Web MD article with the nutritional content of different brands. –  BackInShapeBuddy Dec 24 '12 at 18:20
    
If you have an interest in nutrition, please show your support for this site: area51.stackexchange.com/proposals/44550/nutrition –  Mew Jan 1 '13 at 2:24

6 Answers 6

up vote 14 down vote accepted

My experience with hyponatremia comes from Ironman racing and training. The thing I had to learn to do was to get enough salt into me. Sports drinks have no where near enough, compared to the rate I sweat at. I am at the high end of the range, 1.5L/hr or more. (Measure dry before, go out for 10 hours, track fluid in, rarely end up peeing, weigh after, 1Kilo=1Litre).

1L of sweat has on the order of 1-2 grams of salt.

My issue turned out to be that during the swim, (I am slow, so 1:30 or so) I would sweat so much, but not notice since I was swimming that when I started the bike, I was already down on salt and it just got worse. I started simply eating salt packets from a restaurant evey 1-2 hours. Not too much at any one time, easy to get down, easy to come by, made a huge difference.

But hyponatremia does really suck. I find it makes me fall asleep, even while riding, which is usually my first indication I screwed up. Within moments of the salt touching my tongue, I start to feel better. It is amazingly fast.

The upside is you get to pass out in odd locations, without the use of alcohol! I stopped once 4 hours into a 7 hour ride at 35C, to buy some water and chips. Sat in the shade to eat and drink and passed out. When I woke up and came into the store again they were relieved, as they were planning on calling an ambulance soon.

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1  
Very nice info. So a steady oral intake of small amount of table salt would help significantly, right? I am starting to wonder why do we even bother buying expensive sports drink when we can just add some salt into a bottle of water. Thanks! –  Gapton Dec 31 '12 at 7:52
    
@Gapton The main reason for non-table salt sources is that it can be pretty hard to take at times. Sometimes you can, sometimes you cannot. Getting it in food is a lot easier and more palatable. However sometimes it can be hard to get enough salt any other way. –  geoffc Dec 31 '12 at 14:21

There are two approaches to consider

Electrolyte Consumption:

First, as many other answers have already identified it's important to replenish electrolytes as well as water.

Basically, your muscles need positively charged and negatively charged electrolytes to function properly but your body loses them through sweat when you exercise heavily. Positive electrolytes are involved in muscle contraction whereas negative electrolytes are necessary for retraction/relaxation.

There are a lot of different types of electrolytes but sodium and potassium are the most abundant and easiest to supplement. To supplement your own intake you can either look for a pre-mixed drink that contains sufficient levels, by a mix like Emergen-C Electro (it's sodium free so you'd need to add your own), or make your own based on a recipe found online.

Pure sodium is sold as 'table salt' and pure sodium is sold as 'lite salt' or 'salt substitute'. The ratios/recipe can be found by searching online for 'DYI electrolyte replacement drink'. While a lot of 'snake oil salesman' sell high priced electrolyte supplements, the main ingredients (ie sodium/potassium) can actually be purchased in large quantities for very cheap.

Aside: Sports drinks may contain electrolyte supplements but usually contain more sugar than anything. The famous historical 'gatorade' mix that the sport drink was closer to a bitter tasting pure electrolyte mix than the sugar water that's sold in stores today. Food for thought if you're trying to reduce unnecessary carb intake.

Change the way you drink water

The way you drink water is as important as how much you drink. It takes some time (as well as sufficient electrolyte balance) for your body to absorb water. It may feel refreshing to chug large quantities when you're thirsty but your body will flush the water it can't absorb as well as additional electrolytes.

It takes a little time to train yourself to do it unconsciously but it has a noticeable benefit during exercise.

Aside: I learned this from one of my wilderness instructors on a month long backpacking trip across The Superstition Wilderness of AZ.

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What do you mean by "your body will flush the water"? As far as I know the only way for water to reach the bladder is through your blood, unless you have diarrhea and the colon doesn't absorb water reliably. –  Baarn Jan 1 '13 at 10:58
    
@Informaficker That's the problem. Too much water in the blood means the kidneys have to work much harder to maintain a healthy balance. Drinking more than the kidneys can effectively handle and may cause kidney damage or other problems (ex hyponatremia, cerebral edema). Food in the digestive tract will help slow absorption but for extended activities (hiking, endurance running) the impact of of that will be lessened over time. –  Evan Plaice Jan 2 '13 at 19:44
    
(cont) Think of it this way, consuming additional electrolytes stimulates absorption of water into the muscle mass. Whereas, preventing over-consumption by sipping smaller amounts of water over time reduces the amount your body has to overcompensate to maintain a healthy water balance. –  Evan Plaice Jan 2 '13 at 19:50

Saw a documentary on this and they went into a lot of science regarding this. Their conclusion -Ask the army. They've been training people for thousands of years.

Basically just drink when you're thirsty.

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I highly doubt that the solution to a lot of science is to ask the army and come up with an even simpler answer. –  Baarn Dec 28 '12 at 21:25
    
What I mean, there are a lot of bad documentaries out there. Your answer is basically just the last sentence - one line - far too short to address the question. –  Baarn Dec 28 '12 at 21:27

This is a pretty complex topic, but I'll share some of what I learned from long-distance (> 10 hour, > 150 mile) bike rides.

Though many people talk about electrolytes in general, the major concern is sodium. This is because the electrolyte that is most prevalent in sweat is sodium, and because the reserves of sodium in the body aren't very big.

Whether you become hyponatremic depends on two factors:

  1. How much sodium you are losing.
  2. How much sodium you are taking in.

How much you are losing depends upon your personal genetics and your training. Some people have sweat that is saltier that others. If you regularly train in hot weather and sweat a lot, your sweat will become less salty.

The amount of sodium you can lose is significant; some people lose in excess of 1000mg of sodium per liter of sweat.

How much you are taking in depends on what you are eating/drinking. If you eat restaurant or prepared food, you are likely getting a fair amount of salt in your diet, but if you are eating a better diet, you may not be getting a lot of salt.

Since everybody is different, it's important to determine whether this is an issue for your and whether you need supplementation. You can do this by weighing yourself before and after your exercise; if your weight has gone up, you are hyponatremic. Another symptom is swollen hands and not needing to use the bathroom even through you have drunk a lot of water. If you spend a lot of time in the bathroom later after you have eaten something with salt in it later, that's another good indication.

If you are not gaining weight and you are going to the bathroom, you probably aren't hyponatremic.

The mechanism for this is interesting; your body loses some sodium when you excrete excess water. When your blood sodium gets low, your body tries to conserve that by slowing down the kidneys, and it stashes the excess water between cells, swelling up the body and making you heavier.

If you need supplementation, there are a few option:

Sport drinks. Most sport drinks don't really have a lot of sodium in them; Gatorade has about 440mg/liter and it's on the higher side.

Electroyte drinks. A drink such as Nuun has about 320 mg per serving.

Electrolyte tablets. These are the big guns in sodium replacement; Succeed S-Caps have about 320mg per capsule.

Real food. I carry some salty real food; something like beef jerky has impressive amounts of salt in it.

If it's a long & hot day, I will have one bottle with sport drink, one with nuun, and I'll also take a couple of electrolyte capsules per hour. I also carry beef jerky and salty crackers.

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Hyponatremia is a deficiency in sodium. (hypo = low level/not enough; natrium = sodium; -emia = in the blood... not enough sodium in the blood).

Not enough is not an absolute value, but a concentration value. The more water you drink the more sodium you need.

Sweat mineral composition

As you can see in this paper, sodium is the main mineral that will require supplementation during exercise as far as sweat loss is concerned... Assuming that your diet is consistent with the RDA and that you sweat less than 4 liters.

The exact minerals lost through perspiration varies from person to person, and for the same person, from day to day. That makes for a lot of individual variations from the base model.

If you sweat more or if your diet is deficient to start with, other minerals can become an issue.

As far as losses through sweat are concerned, sodium is the key... BUT sodium and potassium (and magnesium) work together in opposite ways.

Sodium attracts water in the blood, potassium attracts water in the cells. When blood sodium levels drop compared to the potassium levels, free water is attracted in the cells. Inversely, when sodium levels are high and potassium levels low, free water flows from the cells into the blood stream and the cells are dehydrated (= headaches).

Since the loss of sodium through sweat is the most critical, you have to supplement in sodium, but if by doing so you create an imbalance with the potassium, you may develop headaches.

As with sodium, concentration is important. If you drink a lot, you need more potassium to keep the concentration to its previous level.

If you have headaches after exercise, most likely you need to up your potassium intake.

Amongst the natural "sport friendly" sources of potassium you have:

  • Banana
  • Coconut water
  • Dried apricots
  • Dried peaches/prunes

Given the extend of individual variations, diet, etc. the best is for you to experiment conservatively to find what works for you.

To avoid headaches, don't wait until you have one to start taking electrolytes. When you start getting tired, hot, your mouth feels a bit dry, your tongue swells up, your hands feel a bit clammy, etc. Or even before any symptom if you notice you are sweating a lot.

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How hyponutremia affects your body:

Your body likes to maintain homeostasis (remain in the same state). When you sweat profusely you are losing a lot of different minerals. If you enter a state of hyponatremia from having too low of sodium in your system your body tries to compensate. This can make you feel lethargic, cause cramps, and some other cause some other symptoms... Most of which (provided there are no other underlying issues) are extremely dangerous. In extreme cases you can enter convulsions, lose consciousness, or possibly fall into a coma.

Being treated for hyponatremia incorrectly can cause Central Pontine Myelinolysis. CPM (in this scenario) is caused when high levels of sodium (from a Saline-drip, for example) are introduced into the body causing a rapid increase in sodium levels. Think about "the bends" but instead of your blood vessels being affected, your central nervous system is affected.

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how does this answer the question? –  Baarn Dec 24 '12 at 8:22
    
"I want to find out what the body looses with excessive sweating..." Hyponutremia only pertains to sodium levels. I was explaining what the body was losing and the effects of over correcting. I can not, in confidence, answer what he should eat/drink to replace the nutrients. –  Grohlier Dec 24 '12 at 21:10

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