Boston Marathon

Is There Any Science Behind Carboloading?

Spaghetti noodles made in a pasta-making class at Dave's Fresh Pasta in Somerville, Massachusetts. Charlie Mahoney for The Boston Globe

A big pasta dinner is the classic pre-marathon tradition. Carboloading, as it’s known, means filling up on carbs right before a big race. The idea is that, if the body can store more carbohydrates as glycogen, a fuel source for muscles, then a runner will have more to burn, and thus more energy to perform.

But is there any truth to carboloading?

“The concept behind carboloading came from studies a long time ago,’’ says Krista Austin, Ph.D., who worked with 2014 Boston Marathon winner Meb Keflezighi.

The studies, for the most part, involved glycogen depletion and loading, she says. This means athletes would follow a low-carbohydrate diet, then load up on carbs and see their performance spike. The problem is that when training tapers off, the body is not burning as much glycogen, so the muscles store more, she says.

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“The word carboloading is defective,’’ adds Nancy Clark M.S., R.D., a sports nutrition counselor and team nutritionist for the Red Sox. “People think it means stuffing yourself with pasta the night before, but we should think about carbs in the sense that on a daily basis, you want to make sure your diet is supporting your running program—and that’s done with carb-based meals.’’

But why? Carbohydrates are stored in the muscles as muscle glycogen, says Clark, and depleted muscle glycogen is associated with fatigue. That’s why a steady food plan matters. Instead of drooling over a single pasta dinner, it’s more about balance for the long haul. Every meal should have carbs — oatmeal for breakfast or a sandwich for lunch, says Clark.

“What we encourage is a regular mixed diet that’s 45 percent carbs, with the proportions of carbs, protein, and fat similar to that of your day-to-day basis,’’ Austin says.

In fact, the key is staying consistent with small, frequent meals throughout training.

“What people have to realize is the nutrition during training shouldn’t be that much of a change — it’s usually more about maintaining patterns,’’ she says.

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The one time during training that it makes sense to change your diet? The last three days before a race. Here’s why: High-fiber carbs like brown rice and whole-wheat pasta can lead to gastrointestinal discomfort, which isn’t something any runner wants to deal with on race day. A few days before the race, swap out fiber-rich foods (like brown rice) for low-fiber options (like white rice), says Austin.

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She advises runners to aim for 10 grams of fiber a day in the days leading up to a race — and to have fiber earlier in day so that, at night, you can eat white pasta and it will go through the body easily.

“That way, we don’t have things sitting in gut that might cause GI distress’’ Austin says.

The night before the race, focus more on the amount of water and electrolytes you’re taking in than on how much ziti is on your plate.

Read more coverage of the 2015 Boston Marathon.

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