Does Carb-Loading for a Marathon Really Work?

From the WebMD Archives

By Tom DiChiara

The Rumor: Carb-loading the night before a marathon will keep you from "hitting the wall."

There I was, at mile 22 of the 2008 New York City Marathon... and walking. Sure, I'd heard the woeful tales of runners "hitting the wall" or "bonking" at mile 20, but it never occurred to me that I might someday join their ranks. In anticipation of what was to have been my triumphant marathon debut, I'd logged 70-mile weeks, done the requisite 20-mile runs, tapered my training and eaten a gargantuan pasta dinner the night before -- everything I thought I was supposed to do.

So where had I gone wrong? As I stood at the mile 23 aid station pounding Gatorade, it hit me: Perhaps I hadn't properly carb-loaded -- which, for the uninitiated, is the process of building up glycogen stores in your muscles so that you can burn those sugars when you need them most (like, say, between miles 20 and 26 of a marathon).

What I've learned since, and what has enabled me to successfully finish half a dozen subsequent marathons, is that carb-loading is a far more scientific and complicated process than just shoveling a plate of spaghetti down your gullet 12 hours before a race. So how does it actually work? I did the research, so you'll be better prepared than I was for my first marathon.

The Verdict: Carb-loading for three days prior to a marathon will help keep the crash at bay

"The biggest mistake marathoners make is eating an extra-large dinner the night before the race," says Stuart Calderwood, a senior editor with New York Road Runners (the group that puts on the NYC Marathon) and the veteran of some 56 marathons. "What they should really be doing is eating a larger-than-usual percentage of carbohydrates for the whole last three days, and then eating a normal-sized and familiar dinner."

Going Gaga For Glycogen

Calderwood knows what he's talking about. According to research from the Mayo Clinic, athletes use up their normal stores of glycogen after the first 90 minutes of continuous exercise -- which, unless you're going to set a 33-minute world record for the marathon, is far shorter a time period than you'll be running.

In order to build up glycogen reserves plentiful enough to get you through the second 90 minutes and beyond, you should begin slowly increasing carbohydrate intake about a week before the marathon, making starches about 50 to 55 percent of your total caloric intake. Three days before the event, Mayo recommends that you up that number to 70 percent of your calories. The important thing to remember here is that while you're increasing the percentage of carbohydrate calories consumed, you should not be increasing overall calories -- which can lead to bloating and weight gain. The week before a marathon is when you should be tapering, or decreasing your mileage, to rest up for your 26.2-mile challenge, so you'll be naturally growing your glycogen cache without the need for overeating.


Drink To A Strong Finish

Now that we've established the percentage of carbs you should be consuming, the question remains: How should you get those carbs? While traditional thinking has been to scarf plenty of grains, that's far from the only -- or best -- option. A smart way to top off your glycogen stores without loading up on breads and pastas, which have a tendency to make you feel full and mess with your digestive tract (fun!), is to drink carbohydrate-rich beverages in the three-day run-up to the marathon.

U.S. Olympian Dathan Ritzenhein, who finished fourth at the 2012 U.S. Olympic marathon trials, is a big proponent of this approach. "I get in about 500 calories throughout the day [from high-carb beverages], so it's like another meal, but it doesn't make me feel full," he told Runner's World last year.

Consuming your carbs in this fashion delivers the tangential benefit of hydration, another key component of marathon preparedness. You just have to make sure you pick the right beverages to imbibe. (Hint: Soda isn’t the wisest choice) With double the calories of regular Gatorade, Gatorade Prime is an excellent option, while fruit smoothies like Jamba Juice are a solid source of liquid carbs for those looking to go the all-natural route.

Getting It Right On Race Day

Even if you've logged the miles, hydrated properly and aced your carb-load, there are no guarantees that you'll avoid smashing into that wall on race day. But there are steps you can take to prevent it. First, eat a small familiar breakfast (i.e., something that won't upset your stomach) a few hours before the run. Second, drink Gatorade and take carb gels whenever you feel you need them during the race (but don't overdo it). Third, run at an even pace -- you'll conserve more glycogen that way than if your mile splits are all over the place. Finally -- and this can't be stressed enough -- don't go out too fast! If you run the first 13.1 even 1 percent too fast, you could have a date with the wall a little farther down the road. And, as I believe I've made clear, that's not the least bit fun.

WebMD Feature from Turner Broadcasting System
© Turner Broadcasting System, Inc.


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