I'm enjoying many of the discussions we've been having at ScienceBlogs about the importance of diet and exercise in maintaining health and sustaining weight loss. However, this discussion has reminded me that, for most people, knowledge about diet and exercise has two sources -- 1) What people believe to be true and 2 )What the there is evidence to support.
After yesterday's class the instructor reminded us all to drink "plenty of water." The woman next to me asked, "how much should I drink?" and the instructor replied "as much as you can. You can never have too much water."
That's when I was reminded about some of the recent comments on my blog and knew I needed to post. You see, remaining hydrated is important and one of the biggest pieces of advice given to novice athletes and new dieters is to drink "plenty of water". Drinking water until we feel like our eyes are floating is one of those pieces of advice that has been repeated so frequently that it almost carries the weight of Gospel. Remaining hydrated during and after exercise, especially when the weather is warm, is important. However, it is possible to drink too much water, especially during the summer months, and the consequences of that can be dangerous.
Osmosis is the movement of water from an area of high solute concentration to an area of low solute concentration. If the extracellular fluid (ECF) around the cell is hypertonic (the solute concentration in the ECF is higher than in the cell), water will move out of the cell. If the ECF is hypotonic (the solute concentration in the ECF is lower than in the cell), water will move into the cell. When the ECF is isotonic (there is no difference in solute concentration between the ECF and the cell) there is no net movement of water.
Here's a cool picture to illustrate the point:
Figure 2: The cells on the left are bathed in a hypertonic solution. Water leaves the cells, causing them to shrivel. The cells on the right are bathed in a hypotonic solution. Water enters the cells, causing them to swell and lyse. Image from the Wikimedia Commons database.
Drinking enough water when we exercise is important to prevent dehydration, or to replace water loss due to sweating. However, when we sweat we lose both salt and water. Replacing sweat loss with only water dilutes the salt concentration of plasma and extracellular fluid, causing it to become hypotonic. The effect of this with light to moderate exercise and reasonable water consumption is mild, the kidneys are able to aid in the maintenance of plasma sodium, and the water consumption does not result in physical symptoms. The overall result is rehydration. With more severe exercise resulting in heavy sweat loss and pure water replacement, or just excessive water drinking, the plasma and ECF can become more severely hypotonic and the body's fluid management systems not able to compensate -- a condition known as hyponatremia (literally "low sodium"). Just like the red blood cells in the picture above, when cells are exposed to this hypotonic solution, they swell. One of the most important sites this happens is the brain. Someone with mild hyponatremia may experience nausea, headache, and general feelings of tiredness. More severe hyponatremia can result in profound cerebral edema, confusion, seizures, coma, and death.
Indeed, in a study performed in 2002 and published in the New England Journal of Medicine, investigators measured serum sodium in more than half of the finishers of the Boston Marathon. They found that 16% had hyponatremia. 0.6% had critical (potentially dangerous) hyponatremia. Risk factors for developing hyponatremia included considerable weight gain during the race (over drinking), longer than average race times, and an extreme body mass index. The conclusions of this study lead me to wonder whether individuals trying to lose weight or begin an exercise program are being appropriately counseled in the consumption of water. On one hand it is important to prevent dehydration and many report a sensation of fullness with water consumption that may aid weight loss. On the other hand, too much water without sufficient sodium replacement is clearly problematic.
Dr. W. Larry Kenney, past president of the American College of Sports Medicine and Professor of Kinesiology at the Pennsylvania State University had this to say on the issue of dehydration versus overhydration:
While hyponatremia has gotten more attention lately, far more athletes are affected by dehydration. However, there are dangers associated with both extremes of behavior -- severe under-drinking and severe over-drinking. Not drinking at all is not a safe option for preventing hyponatremia. The key is 'drinking intelligently, not drinking maximally.'
So how much water do we need when we exercise? Here are the evidence-based recommendations direct from the ACSM:
So, that's it. You can weigh yourself after an exercise bout to know how much water you've lost, but drink over time rather than in a single replacement, don't drink when you're not thirsty, and consider sodium-containing snacks or fluids when you've engaged in prolonged exercise.
Drink to Match Fluid Loss and On a Schedule. The experts concluded that appropriate fluid intake (before, during and after exercise) is important to help regulate body temperature and replace fluids lost in sweat. Since fluid and electrolyte needs are widely variable based on the athlete's genetics and environmental conditions, athletes should know their bodys' hourly sweat rate (weight lost during exercise per hour + fluid consumed during exercise per hour = hourly sweat rate) and aim to replace the total amount lost during that time.
According to the previously published ACSM Exercise and Fluid Replacement Position Stand, athletes are encouraged to drink early and at regular intervals rather than rapid fluid replacement. It is noted that perception of thirst, an imperfect index of the magnitude of fluid deficit, cannot be used to provide complete restoration of water lost by sweating. As such, individuals participating in prolonged intense exercise must rely on strategies such as monitoring body weight loss and ingesting volumes of fluid during exercise at a rate equal to that lost from sweating, to ensure complete fluid replacement. Drinking over a set period of time is more effective for complete rehydration as rapid replacement of fluid stimulates increased urine production, reducing body water retention. If athletes are not sweating heavily (such as slow runners) and are not thirsty then their fluid replacement needs are probably modest.
Consume Salty Foods and Beverages. According to the published roundtable report, research shows foods and beverages with sodium help promote fluid retention and stimulate fluid intake. The report also notes that athletes performing prolonged exercise should ingest snacks or fluids containing sodium to help offset the loss of salt in sweat, in an effort to prevent hyponatremia.
Medicine & Health
Life Science
Comments
This is a thoughtful, evidence-based post. Unfortunately, the message is too complex for the general public. How much do you sweat during exercise? Most people don't sweat enough to change their body weight, even though they soak their pits. I mean, not-too-little, not-too-much is the correct answer, but my patients want a more specific answer.
The nice thing is that most folks aren't running a marathon or other extreme event. If most sip some water during activity, have something salty, and drink to their thirst, they will be OK because their kidneys will do the fine-tuning. Outdoor activities in summer heat (like 2-a-day football practices) should follow the same sorts of rules, although the use of Gatorade or other electrolyte drinks should be considered for at least part of the fluid intake.
Back in the old days when I was growing up (1970's) athletes were routinely given salt tablets during outdoor summer training. This practice seems to have been supplanted by sports drinks. It's a pity, since a salt tab can give one more salt in less fluid, without all of the sugar (important for those exercising for weight loss).
Posted by: Pascale | August 12, 2009 1:06 PM
Check out this recent APS Podcast on the same topic: http://scienceblogs.com/isisthescientist/2009/08/how_much_water_do_i_really_nee.php
Posted by: Rebecca | August 12, 2009 1:24 PM
Pascale--I tend to mix up some lemon flavored Crystal Light Hydration packets with my water on my long runs, it has electrolytes in it. They also make a diet version of Gatorade without all the sugar. I prefer those anyway, since drinking something sweet after exercise seems nasty to me.
As for the amount of water to drink, my trainers have told me to check my urine. If it's dark, you need to drink more, and if it's clear, you are probably drinking too much. They say to aim for the color of lemonade.
Good post, Isis! I don't think many people know you can actually drink too much water.
Posted by: Minerva | August 12, 2009 1:30 PM
Oops! Here is the right link: http://lifelines.libsyn.com/index.php?post_id=500412
Posted by: Rebecca | August 12, 2009 1:32 PM
After my exercise yesterday (which was before dinner) I had a package of saltines on my desk and they tasted phenomenally good. Perhaps it was the delicious salt.
Minerva, I'm sure more people are familiar with hyperhydration from that "Hold Your Wee for a Wii" incident.
Posted by: Colin | August 12, 2009 1:34 PM
This was actually an issue for us at basic training (air force.) We were encouraged to drink a pretty fair amount of water, because we were losing water all day long from sweating, but they did warn us to avoid too much. Mostly they told us to drink so much per half day, and we had a certain amount at each meal, and to watch the color of our urine. You were pretty much shooting for almost clear, they had a little chart on the wall and everything. Obviously dehydration was a bigger issue (I actually messed that up one of my first days and got a bit light headed for a short while, even for someone who grew up in florida it was a lot of sweating) but they were aware of and watching for hyponatremia.
Posted by: Seldon | August 12, 2009 1:34 PM
As a career Soldier, I know this topic well.
When I was but a young troop-ling going through my paces as a cadet, I remember vividly being told to hydrate constantly, even if your stomach was so full of water that to drink more would induce vomiting. I knew a few other cadets who drank constantly who became sick, and I was thoroughly shocked that the instructors simply parroted that they were de-hydrated.
The Army is slow to change, however, and to this day I find Soldiers in my Command - both young and old - who simply do not believe that you can over-hydrate. I have had to order NCOs to educate themselves better on the topic to avoid spreading the wrong information to junior Soldiers.
Posted by: Mystyk | August 12, 2009 1:40 PM
Edit for the non-military: "NCO" = Non-Comissioned Officer (senior enlisted ranks; sergeants, etc.)
Posted by: Mystyk | August 12, 2009 1:42 PM
Great post, Isis! For once I do something right.
My uncle is a construction worker and tells the story of a colleague who worked in the hot sun all morning long, and at lunch was so hot that he drank a gallon of ice water to cool down, then promptly suffered a heart attack. In family lore, the heart attack was because of the "shock" to his system from all that cold water.
Is there any physiological reason to go for water of a certain temperature after exercising?
Posted by: ScienceWoman | August 12, 2009 1:57 PM
Here in the hot humid south we have a big problem with hyponatremia every year around marathon time. Everyone is so concerned about drinking enough, then they lose too much salt in their sweat. When the rescue wagon picks them up off the side of the road, their symptoms look like dehydration so the EMTs were pumping them full of *more fluids* rather than stabilizing electrolytes first. After a few incidences like that the race organizers seem to be doing a pretty good job about getting the word out about de- and over-hydration being a problem. You hear the aid crews talking about it too so hopefully the first aid is better informed - now if we could just get all the runners on board.
Posted by: ambivalent academic | August 12, 2009 2:02 PM
thanks for an excellent article!
as a competitive ultramarathon runner, paying close attention to electrolyte balance is absolutely critical. as a starting point, I take several swallows of water every 15 minutes, and a salt tab every 45-60 minutes. I vary this schedule based on heat and sun exposure, urine color, amount of sweat - especially sweat that leaves a salt residue on the skin, and thirst. (thirst is last on my list because once I feel thirsty, I'm already significantly dehydrated - and catching up is difficult from this stage.)
from personal experience, incorporating salt tabs was a huge help in combating dehydration and hyponatremia.
every person is different, and responses to similar conditions vary widely. the most important issue from my perspective is to pay close attention to all of the physiological signals from your body, not just thirst, and to your exercise environment.
in other words, what you said. =)
Posted by: Tim | August 12, 2009 2:03 PM
I don't think so, ScienceWoman. I've heard wackaloon-esque clains that drinking cold things will boost your metabolism, but I have not seen evidence in support of it. I think hyponatremia or cardiovascular disease is a far moe plausible explanation than any half-assed hypothesis I could come up with.
Posted by: Isis the Scientist | August 12, 2009 2:06 PM
Interesting post. I've always been quite self-conscious on hydration (and not afraid to remind others) as I've seen a couple of pretty scary dehydration related incidents out on dive boats but at the same time there is the obvious sense of good things in moderation and the agressiveness with which some people chug bottles of water after exercise/whilst out in the sun leaves me a little nauseous and queasy feeling just watching
Posted by: tai haku | August 12, 2009 2:13 PM
I'm not an elite athlete by any stretch; my average running rate is somewhere around 11 min/mile, but I do sweat a fair amount. I started feeling a lot better and being able to run a lot longer when I replaced my water with low-sugar (homemade) Gatorade for runs over 45 minutes or so. It might have just been a placebo effect, but it did seem to make a difference to me.
From the recommendation about drinking to match sweat rate, it sounds like the goal is to not lose or gain any weight during an exercise session. Am I interpreting that correctly? I've seen similar guidelines that you should weigh yourself before and after a workout. If you gain weight, you're drinking too much; if you lose more than about 2% of your body weight, you're not drinking enough. (Obviously you have to estimate weight lost as urine or feces if you "go" between the times you weigh yourself. I suppose if you were really hardcore you could actually weigh that too, but I think that might be a bit much...)
Posted by: Dr. Kate | August 12, 2009 2:22 PM
Well, there is the simple fact that cold water would incur warming in your body. If exercising then I could see it helping remove heat from your torso (such is the same goal of sweating).
Posted by: Colin | August 12, 2009 2:25 PM
Please check that. Many of the sources you quote, as well as others I'm familiar with, suggest that you drink on a schedule because thirst is a lagging indicator.
I'm particularly familiar with the phenomenon of winter dehydration, which is sneaky because in cool conditions we are less prone to feel thirst even when dehydrated. Standard advice (per the NSP Medical Director) is to monitor urine output and regulate intake accordingly; US Army rules are 1000-2000 ml/day depending on body size.
Trust your kidneys -- maintaining serum electrolyte balance is a big part of what they do.
Posted by: D. C. Sessions | August 12, 2009 2:52 PM
Thank you for this post! It applies even to people who aren't exercising or dieting.
I have long followed the habit of keeping a bottle of water on my desk at work. I sip from it all day long, and in this way I consume at least 20oz of water (and usually more) over the span of 8 hours--all while not sweating a drop. Water is my usual beverage at meals, either straight or as hot tea.
A few months ago my doctor mentioned that my sodium levels were "a little low." After a bit of discussion of my water-drinking habits, she made the exact recommendation you did: I should be sure to consume salt. (And it's very nice to have a reply when some busybody starts to lecture me for salting my potatoes.)
Posted by: --E | August 12, 2009 2:55 PM
When I worked for the Forest Service, I once had to drive a wildland firefighter to the hospital for hyponatremia. Working 16 hours days in hot weather and only drinking water. Looked painful. He didn't return to work for several days.
The Forest Service's recommendation was 1 bottle of Gatorade for every 2-3 bottles of water.
Posted by: Suzanne | August 12, 2009 3:19 PM
In regards to burning calories by drinking ice water, another Science Blogger did an excellent post on the issue. Check out Built on Facts, Miracle Diet Through Physics!
http://scienceblogs.com/builtonfacts/2009/06/miracle_diet_through_physics.php
Posted by: James | August 12, 2009 3:36 PM
Wow! Almost as much interest in science as shoes!
Yes, thirst is a lag indicator, but so is weight loss. Drink a little as you go along; if you get thirsty, drink more.
I like the Forest Service recommendation for Gatorade:water ratio; will recommend that to my patients. I see a fair number of athletes with renal issues here in Nebraska.
Posted by: Pascale | August 12, 2009 6:04 PM
Can the body absorb fluids through the skin? I ask because I spent some time near Phoenix when the temps were breaking records one summer.
I swear that when I got in the pool every evening, I could "feel" my body sucking up water. It's possible the water just felt so good I was hallucinating.
Posted by: Donna B. | August 12, 2009 6:31 PM
Check out Built on Facts, Miracle Diet Through Physics!
Leave it to a physicist to do it the hard way. 1 food calorie [i Kcal] raises the temperature of 1 liter of water 1 degree C. So 1 liter of water heated from 0 to 37 gives 37 Calories.
One thing to add about dehydration is that a decrease in performance becomes noticeable at around 2% of body weight lost. Serious problems may occur in the 5-7% loss range.
Posted by: natural cynic | August 12, 2009 7:16 PM
No, you really can't absorb enough to do any good. The skin, after all, is supposed to keep foreign matter out.
Having lived here (Phoenix) since the early 50s, I suspect that your relief at getting into water was simply the cessation of water loss -- which can be pretty fierce. Around here this time of year, natives can sweat out upwards of five gallons a day. The salt balance is something we learned real early.
And don't forget the potassium.
Posted by: D. C. Sessions | August 12, 2009 7:28 PM
Nice post.
One of the more frustrating things about the water-mythology often projected by the "natural health" lobby types is the insistence that "only water counts" (as part of daily recommended water intake), which of course is a crock.
Again, the physiology is not too complicated; when you are losing a lot of water by sweating (exercising in the heat) you are losing salt too, given that sweat is salty; if the loss isn't too much, you will probably replace it handily by putting a bit more salt on your food the next meal or two, and retaining a bit more salt physiologically (homeostasis). If you are exercising / sweating enough to lose a whole bundle of salt, you will need to take active steps to replace.
Put like that it is kind of common sense, which makes it the more frustrating that all the aqua-obssessionalism tends to confuse people so much.
The 2002 NEJM study on the Boston marathon finishers Isis refers to is a classic that a lot of us who teach body water / salt homeostasis tend to use with students. Of course, apart from being a good cue to some of the mechanisms it also tend to show handily the dangers of endlessly repeated and carefully memorised, but poorly understood, advice.
I don't think I quite agree about thirst being a "lag indicator" for the need to drink. The detection systems in the hypothalamus for body osmolarity are pretty sensitive and will probably "see" 1-2% change. So the lag is likely to be pretty minimal. On the other hand, there is no reason to make a big point of not drinking anything if you don't feel thirsty. Sensible moderation is the key, unless you are in an extreme environment or doing something pretty extreme. As DC Sessions notes, if you have functioning kidneys (and luckily most of us do) they will sort all this stuff out without you having to think too hard about it.
Posted by: Dr Aust | August 12, 2009 8:35 PM
PS For anyone interested, a classic and pretty funny story of a famous kidney physiologist doing heroic "self-experiments" on himself with "water loading" (many Litres / day) in the mid 1950s can be found here (sorry, large PDF - warning!).
Posted by: Dr Aust | August 12, 2009 8:40 PM
I remember seeing a program by Dr Alice Roberts on the BBC where she compared drinking plain water and something like gatorade. The athlete that drank plain water ended up urinating even more fluid than the athlete that drank the sports drink. The reasoning was that the plain water caused the electrolyte levels in the body to become more diluted, so the kidneys had to get rid of all that fluid again to rebalance the electrolyte levels..
And then there is the research that shows that beer is just as good as sports drinks for post exercise rehydration.
Posted by: mrcreosote | August 12, 2009 9:13 PM
As a former soldier in the Australian Army & operating during our summers, in temps of 35 degrees regularly doing hard physical exerecise, we were "told to drink plenty of water" - but to also to ensure we pee'd clear at least once per day. This balanced & basic approach worked well & is common sense enough to be applied easily.
Posted by: Simon | August 13, 2009 12:47 AM
Any thoughts on drinking chocolate milk post-exercise? I was at a symposium last year and one of the speakers (a kinesiologist, Stuart Phillips, at McMaster University) said he recommends chocolate milk post-exercise for its protein content (maintain muscle mass) and carbohydrate content (glycogen replenishing), not to mention it does contain electrolytes to help reduce the risk of hyponatremia.
Posted by: x_ine | August 13, 2009 8:01 AM
P.S. For those who want to read more about it:
http://www.milknewsroom.com/downloads/stager_chocmilk_study.pdf
Posted by: x_ine | August 13, 2009 8:06 AM
I am a nurse and worked in oncology for years. Our physicians would tell patients "check the color of your urine." If it is dark yellow, you need to drink more fluids. If it is pale, you are doing OK. Seems easy for lay people to follow this advice.
Posted by: Margaret | August 13, 2009 8:45 AM
interesting note from the neuropharmacologist in the room, since it hasn't been brought up yet:
mdma (ecstasy) users tend to understand that hyperthermia is a side effect of using the drug, and incorrectly try to compensate for it by drinking too much water. hyponatremia can result.
Posted by: leigh | August 13, 2009 11:42 AM
To reiterate the first commenter's thoughts: this is high-level training you're talking about, not your average couch potato trying to get back into last summer's jeans.
Re: half-a-gallon of lemonade all at once causing a "heart attack:" could well have been hyperkalemia, if it was made with real fruit juices and he was already dehydrated and/or hyponatremic.
Re: people who drink plain water urinating more than those who drink gatorade: but that's half the point of rehydration, to keep the kidneys happy. Gatorade is for marathon runners. The weekend warriors really need not worry about it.
And chocolate milk post-exercise: GAG! I love chocolate milk, but I can't even picture that.
My turn to go for a run.
Posted by: red rabbit | August 13, 2009 11:44 AM
JUST AS YOU HAVE TO REPLACE LOST LIQUIDS and excrete the remains
YOU MUST REPLACE SODIUM and excrete the remains
Only in this way can you ensure you covered the losses.
With the invention of refrigeration, salting perishable foods has been greatly reduced and modern man has been oblivious of a general reduction of salt intake. This has exposed the body to the marginal dangers of a minimal salt diet upsetting the critical salt water balance. The dangers of increases in blood pressure, may now be blamed on this minimal diet, making any sudden additional hidden salt intake, cause loss of control of the delicate balance of a low salt diet
WE ARE ALL UNDERSALTED There is now a case, for advocating an "excessive" salt intake which will protect the body from the salt level fluctuations of this low salt diet and hypertension, and the constant shock of "modern living" which constantly pounds our secretion systems .
Posted by: commonsalt | August 13, 2009 4:56 PM
Oh Noes! Not Undersalted!
Dear Doritos,
Please save Humanity.
-love, humans.
Posted by: becca | August 13, 2009 8:59 PM
Commonsalt: It just so happens that I feel terribly undersalted, but I can't find any really good sodium chloride anywhere. Could you help me out?
For those Gatorade buffs out there, an 8-oz. (240-ml) bottle of Gatorade G2 contains 110 mg Na+, which means that G2 contains just about 20 mM Na+. I believe that sweat is somewhat saltier than that.
One of my dearest medical pet peeves is hearing people swear that you'll crumble into dust if you don't drink eight glasses of water every day. Even Snopes has felt compelled to refute that one.
Posted by: Prof. Bleen | August 13, 2009 9:52 PM
Prof. Bleen : salt-is salt-is salt- even if your friend is sweating a salt lick is as good as any. Our Blood serum is that close to looking like seawater. My ONLY criteria for a chef is whether he/she knows the difference between too much or too little salt
Posted by: commonsalt | August 14, 2009 3:27 AM
I've had my own go at debunking the
- fallacy (note shameless plug for own blog...sorry). It has also been extensively debunked in the scientific literature, e.g.
- not hotlinked as I don't want to be spam filtered, but if you Google the doi number (cut 'n' paste) you should get to the papers without difficulties. Both were free full text access last time I looked.
The 8 x 8 thing has, of course, been mixed in with the great "Drink lots of bottled water! Tap is bad!" hype, one of the most successful pieces of marketing of the last 20 years.
Posted by: Dr Aust | August 14, 2009 8:52 AM
Dr Tim Noakes is the man who first pointed out the dangers of overdrinking/hyponatremia. The link gives an interesting history of the slow progress of truth..
Posted by: Doug K | August 14, 2009 3:33 PM
Fascinating read, DougK, thanks for posting the reference.
Posted by: Dr Aust | August 14, 2009 4:08 PM
Here's an esoteric story on a similar topic:
I have a family member with a chronic debilitating disease who has a baclofen pump to treat spasticity. For a while, his wife was giving him LOTS of fluids to prevent urinary tract infections. She finally figured out this had the unfortunate side effect of putting his kidneys into overdrive, which lowered the levels of fluid in his body which increased the concentration of baclofen. This would make him groggy and hard to wake up. I think I remember the doctor treated it with a drug that they give kids to prevent bed wetting.
Posted by: Female Engineering Professor | August 14, 2009 10:36 PM
That could explain why I always end up eating chips & ranch dip after exercising. LOL.
BTW, Dr. Isis, have you tried Zumba? It's totally your schtick and it's awesome!
Posted by: JLK | August 16, 2009 1:59 AM
You still make it far too complex.
Humans evolved as delayed drinkers. If we were not delayed drinkers we would never have evolved to what we are today. Especially early hominins hunting on the dry and hot African plains 0.5 - 2 million years ago would not have been able to capture fast running antelope by outlasting them, causing the antelope to become paralyzed by a too high body temperature and therefore more easy to dispatch (by strangulation) before implements like spears became available. If we had become overwhelmed by thirst and paralyzed by "dehydration", we would not have been able to capture the high protein/fat diet necessary to support our larger brains. We would have gone extinct as did all other hominins except Homo sapiens.
Humans have the most remarkable ability to match their sodium losses in sweat and urine EXACTLY to the level of intake. Since most of us eat far too much salt in our diets we do not need to add any more in the form of a sports drink. Already in the 1970s Dr David Costill showed that the only effect of ingesting a sports drink on sodium balance was to increase sodium losses in urine - just another way to increase the value of your urine. Since we all eat too much salt, adding more simply causes the body to have to excrete more. There is also no evidence that when studied in vivo (that is in real live humans) that the addition of salt to water increases the rate of water absorption. This is another mythology promoted by those selling sodium-containing sports drinks. Nor is there any evidence that muscle cramping and "heat illnesses" are due to sodium deficiency and can be prevented by increasing one's salt intake.
The best advice is simple: Drink to thirst. That is how evolution fashioned us. It may not sell much product but it is the way we are designed.
Posted by: Prof Tim Noakes | August 17, 2009 5:30 AM
Prof Tim Noakes: I agree regarding proof of over fluidisation however Of the non-electrolytes most are manufactured by the body and some can be stored, for example, fats. But electrolytes like sodium chloride cannot be stored nor can they be manufactured in the body. Some of them are needed in such small quantities that they are obtainable from almost any diet; sodium salts, however, are needed in much greater quantity.
The same control mechanism operates when taking in too little water, for he/she excretes more salt and less water. [and vice versa] Death from salt starvation or from thirst are both aspects of the same vital need for a stable saline environment inside the body.
Before the invention of refrigeration The increased consumption of salt to [eg Japan ca. 30 grams,].. over and above the minimum physiological requirement, had a striking result which might be of some importance. This additional salt intake changed the bromine ratio in the diet because crystallized salt used for food preservation has a chlorine-to-bromine ratio of over 2000:1, that is, it contains almost no bromine. As bromine has a sedative effect on the human nervous system one might speculate whether the new circumstances of bromine reduction stimulated greater activity.
Posted by: commonsalt | August 18, 2009 6:32 AM
I think it's a bit blase of Professor Tim Noakes to say that there's no need for people doing intensive exercise to consider salt intake as well as water, although I do completely agree with him that sports drinks are oversold for many people taking only light exercise.
This is an anecdote. I started running in 2002, and have run 4 marathons. I carry both water and isotonic sports drink on long (>~15mile) training runs, but probably not enough to rehydrate completely, so I tend to drink one or two pints of water when I get back. When I first started doing distance training I found myself feeling headachey and vomity shortly after running and I discovered accidentally that eating salt straight from the pot was an almost instant cure.
Of course, this may be a placebo effect, but it is also completely consistent with the contention that I am slightly hyponatremic after long runs and need salt. And worth a go, I would say, if anyone has similar post-exercise queasiness.
Posted by: mel | August 18, 2009 10:55 AM
hi everybody,
this site is very helpful for me,
Last week i got the routine blood test,report shows my sodium level is low due to the medication which i'm taking for epilepsy every day. so doctor suggested me to take more sodium.
but my proble is i have gained baby weight of almost of 25lbs so i'm working out to loose the weight,if i take more sodium, is that makes me to gain more weight or it makes difficult to loose weight?? please give me the solution for my worries.
Posted by: rekha | August 20, 2009 8:35 PM
The restoration of your sodium levels per your doctor's instructions should not result in significant weight gain. But, if you still have concerns I would consider talking to her about it.
Posted by: Isis the Scientist | August 20, 2009 9:50 PM
This is such an informative post and stream of comments!!!! Thanks everyone!
Posted by: AD | August 21, 2009 1:45 AM
Thank you for this very informative post Isis.
Posted by: Marc | August 24, 2009 1:53 PM
If hyponatremia, quote "literally means low sodium" - what is so criminal about restoring sodium levels according to [ Dr Isis ]doctor's instructions ??
No doctor has been taken to court for recommending [over] fluidisation. BUT On the other hand recommending NaCl tablet medication which may have resulted in deadly hypertension, has been prosecuted.
Could it be that today's super advanced medical profession is pussyfooting such a basic component of life - the intra-extra cellular salt-water ratio where sodium cannot be stored and water can?
Bolt's 100/200m parched mouth clearly showed he was temporarily drugged on salt. wow!
Posted by: commonsalt | August 25, 2009 10:12 AM
Humans evolved as delayed drinkers.
I agree with the prof. In my experience as a mountaineer, I have often become very dehydrated without noticing any ill effects, so long as I rehydrate by the end of the day. I feel much better if I have modern high energy snacks along the way, but this does not appear to be essential.
Posted by: Kea | September 2, 2009 9:26 AM