I finished Tim Noakes' recent book "Waterlogged: The Serious Problem of Overhydration in Endurance Sports," over the weekend, and thought I'd share a few thoughts on the matter. For a thorough break-down of the book's core ideas, see this excellent review by Joe Uhan of irunfar.com.
The basic premise of Dr. Noakes' book (and much of his other research) involves the capacity of healthy human beings to subconsciously self-regulate when under duress. In other words, the human body is not a "catastrophe" waiting to fall apart when its physiological limits are reached (a "brain-less" mode of exercise), but rather a regulated system which makes allowances based on a reading of its situation at any given moment.
In a running race, this model suggests that the subconscious brain (sometimes called the "Brain-based" or "Central Governor" model) devises a pacing strategy that allows you to finish the race quickly, but without killing yourself in the process. Everything, from your own physiology, the relative importance of the race, and the environmental conditions all factor in to the constantly adjusting calculation. That catastrophes do occasionally happen in sport suggests it is possible that humans can override the governor, but at a high cost.
With that said, the regulatory model discussed in "Waterlogged" is concerned not with physiological limits in exercise performance, but hydration. To my mind, Dr. Noakes makes a compelling case that the best way to take fluids during exercise is to trust your thirst and drink only when thirsty.
This is not a novel idea--it was typical advise once--but it is contrary to what many today seem to believe. Such dogmas include that we should drink ahead of thirst, because thirst is not an accurate gauge of our body's water needs. Furthermore, we should drink something with electrolytes (like Gatorade) to replenish those we lose through sweat. Athletes with "salty sweat," or those with salt stains on their skin at the end of a run are at particular risk, because they lose sodium at a faster rate than most. And if your urine is anything but clear, you're dangerously dehydrated and need to drink more immediately.
According to the research cited by Dr. Noakes, all of these claims are false:
The only symptom of dehydration is the sensation of thirst: if you don't feel thirsty, you're probably not dehydrated.
Drinking an electrolyte solution while exercising probably won't improve performance (interestingly, ingesting a carbohydrate beverage will), and it won't protect against low-sodium medical conditions like Exercise Associated Hyponatremia (EAH) or Exercise Associated Hyponatremic Encephalopathy (EAHE). The only way to reverse EAH or EAHE is an injection of a concentrated hypertonic solution of 3-5% saline. By comparison, Gatorade (and any tolerable drink) is hypotonic, which means it has a sodium concentration of less than 0.9%. In other words, when it comes to electrolyte balance, drinking water or Gatorade amount to the same thing. And according to the research, the primary way people reach such low blood sodium concentrations (135mmols or lower to be classified with EAH) isn't by losing sodium through sweat, respiration, or urine, but by drinking far more than one's body needs or can handle.
So-called "salty sweat" and "salt stains" do not indicate an abnormal sweat sodium concentration all the time, but rather that the person has more sodium at the time than their body needs; salt stains on the skin are just excess salt, nothing more. It seems that sodium is a highly regulated resource in the body, and sweat and urine loses are adjusted quickly based on the amount of sodium in one's diet.
Finally, the color and frequency of one's urine is not a clear indication of hydration. Athletes with "excessive anti-diuretic hormone" (a condition known as Syndrome of Inappropriate ADH secretion) can have highly concentrated (dark) urine yet be dangerously overhydrated.
These are just a few of the points raised in the book, but the message seems clear: despite what many say (including the sports drink industry), current science suggests that drinking to thirst not only yields excellent performance (the winners of most races are nearly always the most dehydrated by the end), but also protects athletes from actual and dangerous medical conditions like EAH and EAHE. It's okay to lose weight during exercise, because according to the research blood sodium osmolality--not body-weight--is the regulated variable in exercising humans. If this is indeed true, then weight-loss during exercise is a necessary step in maintaining homeostasis. Is it any surprise that people who drink to thirst not only lose weight during exercise, but also see their blood sodium concentrations rise?
"Waterlogged" is a highly stimulating book, and I encourage you all to give it a read and judge the evidence and argument for yourself. I feel very fortunate I didn't killed myself during my first marathon by trying to "stay ahead of thirst," and hope to use the knowledge acquired from this book in training for the next the race this October. I may not run faster, but hopefully my chances of ending up in a medical tent are greatly reduced. Something to think about anyway.
Happy Wednesday, friends :)
Gatorade IS a carbohydrate beverage. On a hot summer day with intense prolonged activity, drinking an excessive amount of water and nothing else might result in hyponatremia, however replacing the water with Gatorade will reduce that risk significantly. They certainly do not have the same effect in this case.
ReplyDeleteI suspect there is something to be said for the carbohydrate content in Gatorade. For those adjusted to highcarbohydrate diets, this does appear to improve performance.
ReplyDeleteHowever, the evidence cited in the book is compelling with regard to hyponatremia; that drinking Gatorade is essentially no different from drinking water. Overdrinking of either dilutes the blood-sodium concentration. Indeed, even the typical 0.9% saline solutions(isotonic) used in hopsitals--which is a higher concentration than Gatorade--does not have a sufficient sodium content to reverse hyponatremia (in fact, it exacerbates it further), and some patients have died because they were given 0.9% instead of 3% solutions.
Give the book a read if you have time and find the subject interesting. It's controversial but completely evidence-based. You'll have to judge for yourself, however.