The human body is not designed to absorb food or drink while running. That’s because eating and drinking on the run are very new behaviors for our species—something we started doing in earnest a few decades ago and never did for about two million years prior to that time. Anthropologists believe that early humans did lots of long-distance running, but our ancient ancestors had no way of drinking as they ran—no squeeze bottles or CamelBaks to suck from—and because most of the running they did was in fight-or-flight situations, eating had to wait until after the task was completed. There was no survival advantage associated with being able to drink or eat while running, for the simple reason that nobody ever did it. Thus, although early humans underwent many evolutionary adaptations that made them better runners, they did not evolve in ways that made them better able to eat or drink on the run.
This evolutionary inheritance can be clearly observed today in the physiological effects of running on our digestive system. When we start to run our body shunts blood flow away from the digestive organs to the muscles, impeding the breakdown and absorption of food. Hormonal changes cause appetite to disappear and slow the digestion of anything that is consumed. The faster we run, the slower the stomach empties. And to cap it all off, the sloshing of the stomach contents that occurs during running causes feelings of discomfort similar to those experienced by a kid who rides a roller coaster after eating a Coney Island hot dog.
Together these factors add up to a simple message from our body to our conscious faculties: Do not eat or drink while running. We can disregard this message to some degree without suffering ill effects. But drinking or eating more than a modest amount while running is almost certain to cause debilitating gastrointestinal symptoms.
On the other hand, drinking (and perhaps also eating) a tolerable amount of the right stuff enhances performance in marathons and half marathons. To eat and drink nothing therefore is to needlessly limit one’s performance. Optimal race nutrition is a balancing act. The object is to consume enough of the right stuff to push back the wall of fatigue but not so much of anything that bloating, sloshing, nausea, or worse causes you to slow down.
One trick that helps with this balancing act is beginning the race-fueling process before the race itself starts, as I suggested at the conclusion of the previous chapter. To get a meaningful performance benefit from carbohydrate during a race you need to consume at least 30 g of carbohydrate per hour. Drinking roughly 4 ounces of a sports drink or swallowing one packet of energy gel a few minutes before the race starts will contribute 10 to 25 g of carbs toward this quota. Because these carbs will not enter your bloodstream until you’re already running, they count as race nutrition. But because this nutrition is ingested while you’re still at rest, it will be less likely to contribute toward later GI problems than will an equal amount of sports drink or gel consumed within the race.
This little “cheat” is something that almost every runner—even those with a sensitive stomach—can and should exploit at the beginning of every marathon and half marathon. From this point, however, the race plans of individual runners must necessarily diverge. There is no single race nutrition plan that works best for every runner in every race. Different plans work best for different bodies. There are five general marathon and half-marathon fueling strategies to choose from. The strategy that fits you best depends primarily on your tolerance for fluid and energy intake while racing.