Not for Marathoners Only: What Are the Latest Recommendations for Fluid and Carbohydrate Consumption While Running?
Some running topics just never go away. We're always seeking the best and newest answers on these. How much should I drink in a race? How many carbs should I attempt to take in?
The new director of the Gatorade Sports Science Institute, Asker Jeukendrup, has been writing about these old chestnuts in several new journal papers. The information that follows comes from an article in the Journal of Sports Sciences, and summarizes expert opinion from a recent IOC Consensus group meeting on endurance sports nutrition.
How much should you drink in a marathon? Expert opinion now says it's commonplace and entirely okay to finish a marathon about two to three percent lighter than when you started. For the purposes of this blog, I'll use the middle ground–minus 2.5 percent–and assume that you are a 150-pound runner finishing the marathon in four hours.
Since 2.5 percent of 150 pounds is 3.75 lbs (60 ounces), this represents fluid that you don't have to replace during a marathon. Divide by four hours, and it means that you don't have to drink 15 ounces/hour (that you might once have aimed to drink if you were planning to finish the marathon with zero weight loss.)
You can use a similar 2.5 percent approach for your own body weight, be it 100 pounds or 250. The resulting computation will give you an amount that you don't have to drink, because you're no longer aiming to maintain body weight. You still have to figure out how much to drink, which is primarily dependent on your weight, the weather, and your pace.
For the roughly 150-pounder, there's an easier way to get to "the bottom line." The 2007 "Exercise and Fluid Replacement" Position Stand of the American College of Sports Medicine has a table for a 150-pound marathoner finishing in about four hours on a 64 degrees Fahrenheit day. If this runner drinks roughly 14 ounces of fluids an hour, he/she will likely finish about 2.3 percent dehydrated–that is, within the 2.5 percent guideline stated above.
Here are some other runners and drinking amounts from the same table that will result in an acceptable 2 to 3 percent dehydration at the finish. Obvious messages: The more you weigh, the more you have to drink. The faster you run, the more you have to drink. Important corollary: If you are small and slow, you should not drink very much per hour, or you increase risk of hyponatremia. (Remember, these all refer to a 64 F day. Temperature and humidity are huge factors in both directions, high and low.)
|Runner weight||Finish time||Drink rate||Finish % wt loss|
Next, how many carbs do you have to stuff down when you run? Jeukendrup produced a neat chart in his recent article. I've summarized it below. Note that, like others, he doesn't think you need to worry much about carbs if you're only exercising for 30 to 75 minutes. The "mouth rinse" approach is interesting, though, and hasn't been included in past charts of this type.
Jeukendrup is referring to experiments where runners have been told to "swish and spit" a sports drink, but not to actually swallow. A number of these trials have shown improved performance versus a no-drinking condition. Apparently, the mouth sends a message to the brain which says, "Three cheers, sugar is on the way." The brain is tricked, and the muscles too. As a result, you can run faster. These trials have not been extended for periods much beyond an hour. So Jeukendrup believes this is a good strategy if you're exercising for 30 to 75 minutes, but wouldn't work for a full marathon.
Jeukendrup is also a fan of pushing your carb-intake limits. He says his research supports this. (See my interview with him a few weeks ago.) That's why the final row in the below chart shows a carb-intake level up to 360 calories per hour. This exceeds the now typical recommendation of 30 to 60 grams (120 to 240 calories) per hour. I'm guessing (and this is pure speculation) that Gatorade will soon introduce new products to help you push the carb-intake barrier.
|30-75||0, mouth rinse|
|1-2 hrs||up to 120 cals/hr|
|2-3 hrs||up to 240 cals/hr|
|2.5+ hrs||up to 360 cals/hr|