Closed systems that seem to work in a logical manner are comforting. For years it was thought that arteries were just like plumbing conduits and that dietary fat and cholesterol simply stuck to their walls and narrowed the vessel and then one day it became all clogged up and you had a heart attack. That was an attractive simple model - and it was wrong. Now that we are a wee bit smarter we’ve come to see that biological systems aren’t as basic and disconnected as they were once made out to be. Millennia of natural selection have provided us with bodies that are capable, adaptable, and complicated.
It seems the more that is written and advertised about sports drinks, the more confused we athletes become. Not only do we have to concern ourselves with how much to drink, but also what to choose as an energy supply and what minerals seem to be important as well. If one were to gather up all the research papers on this subject, one would likely find a study that supports nearly every possible position one could have. But, after one parsing out those studies that have conflicts of interest or that don’t really relate to our specific needs we can lay down a few generalizations.
First and foremost, don’t drink if you aren’t thirsty. Yes, this is contrary to advice that many of us have grown accustomed to hearing in recent years from the American College of Sports Medicine, but it’s true (see first paragraph). Overhydration can hurt performance and can be rapidly fatal in certain circumstances. We humans are quite good at handling dehydration but we’re less well adapted to it’s counterpart overhydration, particularly when it’s combined with exercise, which when one thinks about it, would be expected as the situation would be quite an odd one considering that our ancestors evolved on land. Our guts can absorb fluids faster than our kidneys and sweat glands can dispose of the excess. “Watering down” our innards wreaks havoc on our biochemistry.
Dehydration from exercise is much less deadly. The main effect of dehydration is that it simply slows one down. However, this is difficult to generalize across athletes as studies looking at weight loss and performance frequently show that the top finishers in endurance races tend to be the most dehydrated. This is not to say that more dehydration equals better performance but only that one cannot generalize and conclude that increasing dehydration leads to worsening performance. Most would agree that 2% drop in body weight during a 2-6 hour event is normal and that performance may not suffer at all. Some would argue that at 4% loss of body weight performance begins to suffer, while others say that even 6% might not necessarily affect performance or health provided the athlete feels alright. The athlete should therefore, in most all cases, expect to lose about 2-4% of body weight over a few hour event while not suffering any loss in performance.
Concerning volume, then, the vast majority of athletes fall within the range of needing about 400 ml to 800 ml of fluids per hour with the lower range for smaller athletes, slower pace, or colder temperatures and 800 ml per hour for larger athletes, a faster pace, or hotter, more humid conditions. How does one know how much to drink? The best advice comes from Tim Noakes MD - drink when you’re thirsty, not before.
What about sodium? Afterall, sweat is quite salty. One needs to replace that, right? I used to be convinced that we needed to replace every last white grain of salt that we lost through sweating so I routinely calculated and measured the volume of salt that I needed to add to my sports drinks to bring the osmolality up to about what I suspected I was losing. Again, that was probably wasted effort. For events lasting for up to 6, 8, 10? hours, some experts, including Noakes, say that it’s probably not important to worry about salt losses because the body has excess sodium that it can pull from tissues to replace that lost in sweat. One caveat to keep in mind, though, is that because it can take from several hours to a few days to adapt from a “salt losing” to a “salt sparing” physiology, it may be wise for endurance athletes to eat a low sodium diet in the week leading up to a longer race so as to place the body’s physiology into a sodium conservation mode before the race begins. Calcium? Potassium? Neither are likely to be important to replace during these shorter races, with “shorter” meaning anything up to a 8+ hours duration.
Okay, so not too much water, don’t fret about electrolytes. What about an energy supply? Carbohydrate is all you need and it comes in many forms including sucrose, glucose, fructose, dextran, waxy maize, maltodextrin. But, it shouldn’t be as complicated as advertisements make it out to be and it’s no surprise that companies patent certain sugar formulations, fund a bit of research, and ultimately hold up “scientific papers” decrying their products as better or best. So who do you believe?When one keeps in mind that there is a mountain of poor quality research, or poorly thought out and often wrong conclusions, and that much of any valid data may not even be applicable to your needs . . . you should then believe your gut and what your brain tells you to do.
The sugar concentration should be in the range of about what you’ll find palatable which is slightly more dilute than the commercial products such as Gatorade. While pure water exits from the stomach faster than a sugar solution does, the latter is absorbed more quickly in the small intestine, and while complex carbohydrates supply more energy and are lower in osmolality for the same energy content, they may have a slower rate of absorption and get metabolized no faster than simple sugars. If your solution is too concentrated the fluid may empty too slowly from your stomach - too dilute and it may be absorbed too slowly from your small intestine. Therefore, going too much in any one direction may make you feel uncomfortable and bloated - and you’ll definitely feel bloated if you drink too much.
In the end, learn to trust your thirst mechanism and your cravings for salt (or lack thereof) and sugar as your body will tell you what it needs. Save your money and don’t stress about not having the latest greatest sports drink or the one that some sponsored athlete is drinking because most everything, including de-fizzed diluted coke, may work just fine. To optimize your performance, start by optimizing your training. Acclimate to the conditions that you’ll race in next.
Finally, choose a sugar solution of your choice to improve your performance and to also provide a psychological boost in both shorter and longer events. And it goes without saying - try your drink in training at least a few times in similar conditions before you rely on it in races.