In a scene from season four of The Office that struck fear in the guts of runners everywhere, Michael Scott demonstrated one way not to carbo load: Downing a takeout tin full of fettuccine alfredo in the parking lot immediately before a Dunder Mifflin 5K.
It’s an egregious example, but far from the only way runners get this scientifically valid principle wrong. When properly applied, two to three days of carbo or carb loading can shave two to three percent off your marathon time, says Kate Davis, a sports dietitian and owner of RDKate Sports Nutrition—that translates to a not insignificant seven minutes off a four-hour race. But all too often, even well-intentioned athletes go wrong. These are the most common mistakes.
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You carb load for short distances.
All the bread, sugar, and cereal you consume turns into glycogen—fuel that’s stored in your muscles and liver to power each contraction of your glutes, hamstrings, and quads, Davis says. Your body can store enough glycogen to sustain you through 90 minutes of moderate running, possibly longer if you’re running a slower pace (say, one you can sustain for all 26.2 miles of a marathon).
Training runs, daily life, and even sleeping deplete your glycogen reservoirs. Making a conscious effort to take in more carbs in the final two to three days pre-race triggers what’s called a supercompensation, allowing you to max out your storage potential, Davis says. As a result, you’ll postpone what’s known in running circles as “bonking” or “hitting the wall”—that sudden, slamming sensation of severe fatigue as your body converts from using glucose for fuel to burning fat.
If your race time will fall under that 90-minute mark, topping off your glycogen stores does you no good—you’d never burn through all your fuel in a 5K or 10K anyway, Davis says. In fact, the strategy may be counterproductive. Because carbs hold water, you’ll gain a little weight and feel a bit stiff, sensations that fade quickly during a marathon but can really slow you down at shorter, speedier distances.
You save all your carbs for the pasta dinner.
There’s a reason nearly every race entry comes with a ticket to a spaghetti feast. Noodles do, indeed, provide ample amounts of carbohydrates—about 40 grams per cup. But that’s still a small percentage of what you need to pack in to trigger carb loading’s desired effects.
Guidelines from the International Olympic Committee recommend nine to 12 grams of carbs per kilogram (that’s 2.2 pounds) of body weight each day for the 24 to 48 hours before your event. If you do the math, a 125-pound runner would need up to 680 grams daily, while a 145-pound athlete would have to reach up to almost 800 grams, Davis points out.
That’s a heck of a lot of pasta if you haven’t prioritized carbs throughout the day. “You don’t want to get to the end of the day and suddenly realize, ‘Oh my gosh, I have to get 400 grams of carbohydrates,’” Davis says. “That’s not really good for your body; it’s not going to feel good to try to cram all that in.”
Avoid the last-minute panic by planning your days ahead of time, and begin them with a large, carb-rich breakfast (think pancakes, fruit, toast, and flavored yogurt). Snack every couple of hours on foods like dried fruit, pretzels, and even hard candy in moderation. “That way you kind of chip away at it over the course of the day,” Davis says.
Don’t forget what goes in your cup, says Laura Moretti, a sports dietitian at Boston Children’s Hospital. Swapping water for more caloric drinks like juice, smoothies, or lemonade can help you add carbs without feeling too stuffed.
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You fill up on processed, high-fat foods.
In many ways, the advice dietitians give for what to eat during carb loading runs contrary to what they recommend for a healthy diet overall. “You’re trying to avoid protein, fat, and fiber; they take a little bit longer to digest,” says Anne Rollins, a sports dietitian for The Core Diet and at Embody Fitness in Burlington, Massachusetts. “Instead, we want to be including foods that break down really quickly.”
That means—just for these few days—eating all the refined-grain foods like white bread, pasta, and rice you’re normally supposed to avoid (since whole grains have more fiber). Also, lay off fiber-rich whole fruits like apples and go for broken-down versions like applesauce or apple juice. And swap green, leafy veggies for starchier choices like potatoes, peas, and sweet potatoes.
But carb loading is not a ticket to stuff your face with junky breakfast foods and desserts, like donuts, scones, and cookies, Davis says. Because they’re high in fat in addition to carbs, they essentially tip you over the edge into just plain overeating, leaving you stuffed and sluggish (another reason fettuccine alfredo is sub-optimal, even the night before).
You skip breakfast on race morning.
Yeah, we know most half and full marathons start early. But if you roll directly out of bed to the starting line, you’re missing out on one last big chance to top off your energy stores, Rollins says. Set your alarm an hour or two earlier—you’ll want some time to digest—and eat a high-carb pre-race meal (Rollins likes applesauce, a Clif bar, and plenty of sports drinks; other runners go for things like bagels, oatmeal, or dry cereal with honey and bananas).
You try it all for the first time on race weekend.
All this comes with a great big caveat, especially if you’re racing right now. While exercise science research has provided general guidelines for carb loading, every body responds a little bit differently. Doing something dramatically different immediately before a big race is always risky, Rollins says.
Instead, choose a few long runs or lower-priority races and test the whole two- to three-day protocol (including carb loading, your pre-race breakfast, and any gels, sports drinks, or other fuel you’ll take in during the race). Keep notes about what you ate the days before—and morning of—and how you felt.
It’s normal—and actually helpful, for an endurance event—to gain a little water weight while carb loading. Any feelings of heaviness from this extra weight usually disappears once you start moving, Davis says. Practicing your routine in training will give the confidence that that’s the case.
If you normally eat a pretty healthy diet, carb loading can cause some digestive distress the first time, since it’s a bit of a shock to the system. But don’t automatically write the whole thing off if you want the extra advantage, Rollins advises. Instead, experiment with different foods, going higher or lower in the recommended range of carbs, or eating at different times until you find a method that works for you.
Plus, once you bump up your carb intake a few times, your body learns to produce the enzymes and transporters needed to break down the sugar infusion more efficiently. “Just like your heart and your lungs, the digestive system responds to training, but it does need to practice,” Rollins says.
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