Old Rule: Drink as much as you can during the marathon.
New Rule: Drink by thirst.
If you’ve been a runner longer than a week you’ve probably been advised at least once — perhaps dozens of times — to hydrate during your race with a sports drink at a rate sufficient to offset weight loss from sweating and to provide 60 grams of carbohydrate per hour. The rationale behind these recommendations is that full rehydration elevates performance by aiding thermoregulation and reducing cardiac strain, while absorbing carbs at the highest possible rate enhances performance by maintaining blood glucose levels and delaying muscle glycogen depletion.
Lately, however, these longstanding guidelines have been challenged by studies indicating that, during running, such high rates of fueling cause gastrointestinal discomfort and offer no performance benefit compared to simply drinking by thirst. A new study conducted by Ian Rollo and colleagues at England’s Loughborough University, published in the International Journal of Sport Nutrition and Exercise Metabolism, provides the strongest support yet for this new “obey your thirst” philosophy.
Nine experienced recreational runners participated in the experiment. Each completed a 10-mile road race on three separate occasions, drinking nothing during one race, drinking a carbohydrate-electrolyte sports drink by thirst during another race (which came to an average of 315 ml per hour), and drinking at a prescribed rate aimed to provide the recommended 60 grams of carbs per hour in the third race (which came to 1,055 ml per hour).
In addition to timing the three races, Dr. Rollo’s team took measurements of dehydration, core body temperature, and gastrointestinal distress. Performances in the no-drinking and prescribed-drinking trials were almost identical. But, when allowed to drink according to their thirst, the runners covered the 10-mile course almost a minute faster on average.
Rollo says that further research is needed to determine why the runners performed better with intuitive drinking, despite becoming significantly more dehydrated and taking in 70 percent less carbohydrates compared to the prescribed-drinking trial. One possible explanation is suggested by the runners’ subjective ratings of gastrointestinal discomfort, which were significantly higher throughout the second half of the 10-mile race in which they were required to drink more than desired.
Take-Away Tip: Drinking a calculated amount of sports drink during a marathon is difficult. Who knows how many ounces will be in that next Dixie cup? Fortunately, you don’t have to drink according to any mathematical formula. Listen to your body to take on only as much as you need.
This piece first appeared in the March 2013 issue of Competitor magazine.
About The Author:
Matt Fitzgerald is the author of numerous books, including Racing Weight: How To Get Lean For Peak Performance (VeloPress, 2012) and The New Rules of Marathon & Half-Marathon Nutrition (Lifelong Books, 2013). He is also a Training Intelligence Specialist for PEAR Sports. To learn more about Matt visit www.mattfitzgerald.org.