More Conventional Wisdoms Bite the Dust (Part I)
As a physical therapy student some 20 years ago, my professors often referred to me by my first name and last initial, as in Gabe “Why.” I guess I earned this moniker as a result of my constant questioning of just about everything they taught. I was never one to quietly accept something as fact simply because some expert “said so.”
Some things never change; I still take a little pleasure in learning that some long-held “truth” has been debunked by researchers, especially when it’s a “fact” about which I have always held suspicions. Two such conventionally-held wisdoms have recently been examined in respected medical journals that should be of interest to runners.
The first “myth” addresses the popular notion – promoted for years by fashion magazines, diet gurus, and grandmothers – that it is advisable, perhaps even necessary, to drink at least eight eight-ounce glasses of water each day. Running magazines and books in particular like to encourage this practice, often stating as fact that the “8×8 rule” is mandatory for good health, good performance, and even injury prevention. But is this fact really true?
Dr. Heinz Valtin, a kidney specialist and professor emeritus of physiology at Dartmouth Medical School, recently published a literature review on the subject in the American Journal of Physiology. Dr. Valtin’s goal was to find the origin and validity of the “8×8” recommendation, but as a result of his investigation he concluded that there is in fact no scientific evidence to support what may be charitably termed a “medical urban legend.” Dr. Valtin does emphasize that these conclusions apply to healthy, sedentary individuals who live in a temperate climate, and that more active individuals (e.g., runners) probably need to consume more fluids, but the amount is dependent on the amount of exercise, intensity, body type, etc. In other words, there is no “standard” amount of water that must be drunk each day by everyone.
So, just how did this “fact” come about? No one knows for sure, but Dr. Valtin suspects it originated with guidelines posted some years ago by the Food and Nutrition Board of the National Research Council (NRC):
“An ordinary standard for diverse persons is 1 milliliter [of water] for each calorie of food. Most of this quantity is contained in prepared foods.” [Italics added]
It appears that the second sentence of this recommendation was either not heeded or ignored, leading people to believe that the equivalent of eight glasses of water must be drunk each day. In reality, most of the foods we eat contain a substantial amount of water, and generally more than enough to supply the daily requirement for most people. What’s more, like all good urban legends, the “facts” supporting this advice has grown over time, even to the point that some proponents have argued that we must force ourselves to drink those eight glasses because our natural thirst mechanism is somehow defective and cannot be trusted. Again, there is no valid scientific evidence to support this rather presumptuous assertion! In fact, it seems to me a bit arrogant to claim that we know better than Mother Nature. And, it turns out, it may actually be dangerous!
As reported recently in Runner’s World Online, the International Marathon Medical Directors Association (IMMDA) has broken with nearly two decades of conventional wisdom about a runner’s need for fluid replacement in a marathon. While acknowledging “the wise doctrine that athletes do need to drink generously during exercise,” the IMMDA Advisory Statement on Guidelines for Fluid Replacement During Marathon Running suggests that most marathoners need consume just 400 to 800 mL (13.5 to 27 fluid ounces) of fluids per hour, as opposed to the 24 to 48 fluid ounces per hour recommended by the American College of Sports Medicine and other major nutrition groups.
The IMMDA issued this statement to “…provide a caution against [earlier recommendations], due to the recent realization that athletes – particularly the slower ones – can drink so much during prolonged exercise that potentially fatal consequences can result,” referring to the small number of deaths from hyponatremia (excess fluid consumption) that have occurred in marathons and other endurance events in recent years.
The moral of the story: respect and trust your body. In most cases, it knows what it’s doing. Don’t try to override your natural instincts just because “someone says so.”