Don’t get me wrong. I’m a big fan of exercise, and a big fan of strength training in particular. I resent the stupid Planet Fitness commercials that make fun of the big, dumb, muscle-bound gym rat that promise you won’t be judged at their gym. Irony much?
But… it is certainly true that the 6-day-a-week barbell crew have some pretty weird ideas about human physiology. Worse, some of their weird ideas come from professional trainers or coaches of high school and college sports teams. Some of it comes from magazines and TV. And of course, the usual source is “I heard that…”
It seems like a lot of these guys have heard that you should drink tons of water when you are exercising. It’s not uncommon when I’m at the gym that I’ll see two or three guys – usually the ones in better shape, though not always – lugging around a gallon jug of pure water. For the record, a gallon is 3.8 L. It’s 128 oz.
That. Is. A. Lot. Of. Water.
This advice is usually supported with the myth that we should drink 8 tall glasses of pure water every day lest we become dehydrated. Now, mind you, even if that were true (which it isn’t), the guy here who is pictured guzzling a gallon of water during a one and a half hour workout is forcing his body to deal with twice the mythically-large daily recommendation over the course of 90 minutes! Another supporting bit of pseudo-wisdom is that if you’re thirsty, you are already dehydrated. This is a bit like saying if you’re hungry, you’re already starving, or if you’re breathing, you’re already asphyxiated. Given the central importance of hydromineral balance to survival, why would anyone believe that we have evolved such a poor water-monitoring physiological system that the drive to drink water is a sign of impending systems failure?
To people who believe in the many wonders of water, the fluid seems to take on amazing magical properties that defy the laws of physics. But it doesn’t. Take a look at that picture again. Look at the bottle. Look at his body. Where does that water go when it goes into his body? Does it turn into some mystical source of work out power? Unfortunately, something far more pedestrian occurs. It goes into his stomach, then his guts, and then his bloodstream. Now, unless he is working out so hard that he is losing a gallon of water in his breath and his sweat, this presents a problem for his bloodstream.
Before explaining the problem, though, let’s deal with the alternative hypothesis. He’s a serious athlete – might it be that over the course of 90 minutes he could lose that much fluid from strenuous exercise? Strength-training athletes typically do not lose the same amount of fluid as someone engaged in cardio exercise such as treadmill, bike, or running sports; during these more dehydrating exercises a fair estimate would be about 1 L of fluid loss each hour. Our strength trainer, by contrast, might lose about a half a liter – certainly not 3.8.
Importantly, though, this won’t be a half a liter of pure water. Sweat is salty as well, containing perhaps 40 mM concentration of sodium (the same ion as in table salt). Sweat is less salty than our blood, but an athlete who sweats out both water and sodium and only replaces the water (from his or her gallon jug) is exacerbating the problem. Water from the gallon jug will further dilute the lowered levels of sodium, a condition known as hyponatremia.
Which brings us back now to the problem. Where does that water go? It goes into the bloodstream, but does it stay there?
Our body is about 60% water, but this water is found in four distinctly different places. There is the water in our blood and the water in our cerebrospinal fluid. Then there is water in the interstitial space and the water inside our body’s cells (intracellular water). The interstitial space is just the fluid around and between our body cells.
The water that gets absorbed into the blood stream doesn’t stay there – it spills over into the interstitial fluid as well. It may stay there, but only if the interstitial fluid and intracellular fluid have the same osmolarity – the same amount of stuff floating in the fluid. An imbalance of osmolarity creates osmotic pressure, which is the tendency for water to move in a way that dilutes the higher osmole area. (The link in this sentence is to a wonderfully entertaining video that demonstrates this effect.)
Drinking a gallon of water is a good way (i.e., a bad way!) to create osmotic pressure. The water dilutes your vascular and interstitial fluid. This effect is even greater if you’ve been losing sodium in your sweat without replacement (for example, you might replace the salt by eating a snack while working out). Because of this osmotic pressure, the water leaves the interstitial fluid and enters the intracellular space.
Two problems occur as a result. First, your cells become bloated and full of water. (Under some conditions, they can even rupture.) Second, perhaps counter-intuitively, blood pressure drops (because of the movement of fluid into the body’s cells). At worst, the heart cannot pump the blood effectively, even leading to cardiac arrest. This blood pressure drop will also impair the ability of the kidneys to remove the excess water to restore the body to normality.
In the worst case scenario, this will kill you. A particularly ugly story of death by water intoxication involved the “hold your wee for a Wii” contest sponsored by a Sacramento radio station. Contestants sat around a table drinking water. The one who stayed at the table the longest without going to the bathroom won a Nintendo Wii. The unlucky winner of the contest went home with her prize to the delight of her children and died several hours later when her brain swelled up with water. Similarly, a healthy young college student also died of water intoxication during a fraternity hazing incident 2 years earlier.
A handful of U.S. military personnel died of water intoxication between 1989 and 1996 as a result of well-meaning, but completely misguided, hydration recommendations. At the time, military personnel were advised to consume 1.8 L every hour when working in hot temperatures. (Compare this recommendation to our gallon-drinker consuming potentially 3.8 L over a 90-minute work out in an air-conditioned gym.) Furthermore, athletes working much harder than our gym rat – marathoners, ultramarathoners, and triatheletes – not infrequently suffer from exercise-associated hyponatremia, a condition that can cause headaches, dizziness, nausea, and even brain swelling and death. The word hyponatremia literally refers to “abnormally low serum sodium,” but this condition is usually caused by only moderate sodium loss coupled with overhydration. Perversely, the symptoms of hyponatremia are very similar to the symptoms of dehydration, and so a sufferer may “self-medicate” by drinking water – which only exacerbates the problem. (Likewise, a misdiagnosis can lead to a mis-prescription of a saline IV which, despite the presence of salt, will make the patient worse. Instead, the recommendation is for a hypertonic saline IV, much more salty than the standard hospital IV.)
Am I saying that our body builder is going to die?
Death by hyponatremia, even during marathons, is quite rare. It is especially rare for healthy, regular runners. For the same reason that it is silly to think we are dehydrated already when we’re thirsty, it is also silly to think that the body doesn’t have evolved mechanisms to deal with the over-consumption of water. With a healthy set of kidneys and a reasonably slow drinking rate (i.e., the guy isn’t chugging half a gallon at a time), much of the extra water will be deposited quickly in the bladder. And, if the body builder isn’t holding his wee for a Wii, it will next be deposited in the sewer pipes. (On the other hand, just like draining water out of a bathtub, it can take time for our kidneys to get rid of excess water. It is estimated that the maximal rate of excretion is no more than 1.5 L per hour, and possibly half that value.)
But this makes it quite plain how ridiculous the habit is of bringing gallon jugs to the gym: we’re just going to pee all of that excess water out. The true athlete wouldn’t want to waste time drinking and peeing – time that could be used getting started on the next set.
Besides making for an inefficient workout, though, just because the body builder is unlikely to die doesn’t mean that the athlete won’t experience subclinical hyponatremia. Drinking all that water likely will lower blood pressure, tax the heart, and cause muscle cells to swell with water. It is difficult to believe that an athlete can get a quality workout with such self-induced physiological handicaps. (Indeed, I can’t help but wonder if our body builder goes home, feels dizzy and exhausted, and thinks he’s had a great workout when he really just might be a little hyponatremic!)
Indeed, no study has shown that athletic performance is improved by overhydration, whereas mild dehydration or drinking moderately when thirsty is associated with the highest levels of performance. Indeed, studies have shown that, among marathon or ultra-marathon competitors, the competitors with the best times lost the most amount of weight during the race. In other words, the ones who drank the least performed the best.
The stakes may not be quite as high for our body-builder friend, but if you want your body in peak condition during the workout so that you can lift your maximal weight, it seems reasonable based on what we know to presume that drinking only when thirsty is the way to go.
Do electrolyte drinks improve the situation? Unlikely. To make the drinks tasty, most sports drinks have levels of sodium lower than the levels lost in sweat, and far lower than the ideal of the interstitial fluid. A better idea would be to eat a granola bar or other dehydrated food source before or at the beginning of a work out (or during a distance race).
Water doesn’t have magical powers, and just because water is “good for you” doesn’t mean having more is always better. We operate best at a particular hydromineral balance, with a particular intracellular volume, and an optimal blood pressure. Exercising hard throws off that balance, but so does consuming several liters of water in a short period of time. Assuming you are reasonably healthy, your kidneys do a remarkable job of removing the excess water and/or excess sodium, potassium, urea, and glucose to maintain those balances.
Under normal conditions (i.e., no heavy exercise), we lose about 2.5 to 3 L of fluid every day, and so that’s how much we need to replace. 2.5 L is about 85 ounces, or about 2/3 of what our body-builder is drinking in the picture. Of that 85 ounces, we get about 45 ounces from our food. Vegetables and fruits in particular are mostly water, but meats and other foods also contain large quantities of water. Some of these 45 ounces come from the metabolism of sugar and fat; the byproducts of our metabolism are water and carbon dioxide.
This leaves 40 ounces to consume in liquid form. Contrary to popular belief, even this doesn’t have to be pure water – milk, juice, soda, coffee, tea, and other beverages are mostly water, and what little solutes they may contain can be eliminated in the urine if they are consumed in excess of need. Despite another popular myth, there isn’t strong evidence that caffeine is a diuretic – so the idea that coffee “makes you dehydrated” is essentially untrue. So, obviously, is the myth that we need 8 to 10 glasses of water a day to avoid dehydration.
Exercising athletes will lose more than 2.5 L of water in a day, often quite a bit more, but athletes who drink just when thirsty consume around a half a liter per hour or maybe a bit more in hot conditions. This appears to maximize performance.
None of this is to say you shouldn’t drink water! You do lose water, and you do need to replace it. What you shouldn’t do is force yourself to drink water when you aren’t thirsty, nor should you neglect eating foods (particularly salty ones) following excessive sweating or excessive water consumption. As the eminent physiologist Timothy Noakes once wrote, only half in jest:
Should athletes drink nothing, or should they drink to ‘stay ahead of thirst’? Or should they perhaps drink according to endogenous biological signals, in particular to the dictates of thirst as do all the rest of earth’s creatures?
In other words, I don’t care if you “heard that” you should drink like a fish from your trainer, or your coach, or the contemptible Dr. Oz. Drink when you are thirsty. And for the love of God, pee when you have to pee. And try to develop Ted Striker’s brand of drinking problem: