The Case for Carbs

Not only are they not all bad—some are surprisingly good for cyclists. Follow along as we demystify this unfairly maligned fuel source

June 18, 2012
cyclists riding on healthy foods
Serge Bloch

For the last 40 years, carbohydrates have been accused of a laundry list of crimes against humanity, including multiple counts of conspiracy to make us fat. This is partly because too many of us fill our bellies with the wrong kinds—breads, chips, crackers, and pastas made from refined flour that's been processed to within an inch of its nutritional life. Cyclists in particular have also gotten confusing messages about carbs thanks to trends like the protein-centric, grain-shunning Paleo diet (Search: What is the Paleo diet?), and from pro riders who have gone public about going gluten-free. All this has many of us pedaling scared from an essential fuel source that makes us faster, fitter, and smarter on the bike. But harnessing the power of the carbohydrate is not as simple as stocking a pantry full of bagels and filling your bottles with sports drinks. To understand why, you first need to consider five irrefutable facts.

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Fact: Carbs make you a speedier, savvier rider—and may even help you get leaner.

Carbs are so powerful, just a hint of them makes you go faster. British researchers discovered that endurance cyclists who swished and spit a carbohydrate beverage without swallowing a drop were able to shave off a full minute in a time trial, while those who swished a similar noncarb beverage saw no performance gains. 

How's that possible? When the researchers did MRI scans of the riders' sweaty ­noggins, they found that when carbohydrates passed over receptors in the mouth—even without sugary sweetness (the solution was flavorless)—reward centers­ lit up in the brain, which in turn provided the impetus to push harder. In other words, the brain was tricked into believing that fuel was on the way, so it gave the okay to the legs to keep cranking away without conserving energy. All this from a swish.

So what happens when you ingest the stuff? Your body uses it to make glucose, or blood sugar, the fuel that drives athletic performance. Within limits, "the more carbohydrates you consume during endurance exercise, the better you perform," says sports-nutrition researcher Asker Jeukendrup, PhD, global senior director of the Gatorade Sports Science Institute. In a study of endurance cyclists completing a 238-mile race, those who took in the most carbs (the mean was 52 grams an hour for the 16-hour event) posted the fastest times. 

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And the benefits go well beyond performance. "All systems and tissues in your body use carbohydrates in some capacity," says Stacy T. Sims, PhD, a Stanford research exercise physiologist and nutrition scientist who has consulted for pro cycling teams. Carbs fuel your immune system, enhance fluid absorption so you stay hydrated, and are even critical for muscle recovery. In fact, if you fail to feed your body the carbs it needs, it will generate them by breaking down muscle tissue. You also need carbs just to think: The brain gobbles glucose exclusively, says Michigan-based sports dietitian Donna Marlor, BSN, RD, CSSD. It needs a lot, even when you ride, because it's busy picking good lines and strategizing your next move in the pack. And maybe most surprising, carbs prime the furnace for fat burning—the process of digesting them stimulates the hormones your body needs to fully break down and use fat. 

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Fact: Not all carbs are created equal, but there's a time and place for most of them.

Carbohydrates fall into two categories, simple and complex. Simple carbs are made from one or two sugars, like fructose or glucose. They're found in such sweeteners as cane sugar, corn syrup, maple syrup, brown sugar, and honey. Because your body digests them quickly, they trigger a quick surge in insulin, the hormone that ushers glucose from your bloodstream into your cells to fuel activity. Refined and processed foods like white bread, white pasta, cakes, and pastries also fall into this category because they're stripped of fiber and other compounds that slow digestion and the insulin response. Simple carbs get a bad rap because sudden spikes and falls in blood sugar have been linked to overeating and, subsequently, to increased fat storage. 

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Complex carbohydrates are made from more than two sugar molecules and take longer to break down in your body, so you have a more measured blood sugar and insulin response. Complex carbs tend to contain fiber, which also slows digestion. About 50 percent of your total calorie intake should come from carbs, primarily the complex variety, says Marlor. Carbs like fruits, vegetables, legumes, and whole grains are lower in calories, digest more slowly, and contain vitamins, minerals, and immunity-­boosting phytonutrients. 

But simple carbs have a place, especially before and during rides when you need quick energy. The good news is that because you're a cyclist, your body is primed to digest and use these carbs while exercising. Muscle contraction stimulates a special protein that transports glucose directly into your cells without insulin's help, says Marlor.  

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Fact: If you feed your brain, you will avoid the bonk.

Your body stores carbs for fuel (in the form of glycogen), but only in a limited supply. How many carbohydrates you churn through during exercise depends on how hard you're going. "You need to start adding carbs after about 60 minutes of activity to maintain intensity," says Sims. Remember that greedy carb consumer, your brain? It monitors your speed and fuel levels much like your car's gas gauge. If it perceives that you're getting low, it will start shutting you down before you hit empty. Studies show that even when you bonk, you've still got glycogen to spare. The brain simply won't let the tank run dry. 

Even more remarkable: Research suggests that your brain may not let you go full throttle off the line if it senses your stores are low. Researchers in South Africa had cyclists perform hour-long time trials, once while carb-loaded and a second time while following their typical diet. Though the cyclists started at the same pace out of the gate on each trial, when they weren't carb-loaded, their wattage dropped after just 60 seconds, long before they could have made a dent in, let alone drained, their stores. Researchers believe that this is because the cyclists' brains sensed that they didn't have maximum glycogen on board and paced them accordingly. The takeaway: Keeping your tank topped allows you to start strong and stay strong.

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Fact: When you're riding, your digestive system can handle more than you think.

Scientists used to say the body can absorb a maximum of 30 to 60 grams of carbs an hour, or one gram a minute, during exercise. Jeukendrup's lab found that athletes can digest more if they take in more than one kind of carb. Remember the different types of simple sugars? Turns out you have individual transporters in your gut that break down each type and shuttle it to your bloodstream. But they can absorb only a fixed amount in a given time period. So if your glucose transporters are maxed out at 60 grams, others, like those for fructose, are still available. In tests, "we were able to increase carbohydrate absorption up to 1.75 grams a minute with a drink blend that included fructose," says Jeukendrup. That's more than 400 calories an hour. 

You need to train your system to handle that amount of fuel, however. "If you only eat 200 or 250 calories an hour in training, your gut won't suddenly accept twice that much during a race," says Jeukendrup. You need to gradually increase your carb intake during training to get in the range of 400. 

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The trick is to meter it out instead of dumping it all in at once. If you're riding longer than an hour and a half, eat every 20 minutes and drink every 15 minutes. Thirty to 60 grams an hour is fine for easy jaunts. For longer, harder efforts, aim for about 80, says Marlor. Sims recommends getting most of those carbs from food, with just 20 grams (about 80 calories' worth) in your bottles to improve hydration without bogging down your belly. And look for drinks that contain a mixture of two or more carbohydrates, like glucose, fructose, or sucrose.

Fact: Gluten-free does not equal grain-free.

Ever since sports physiologist Allen Lim, PhD, announced that his 2008 Garmin-Slipstream riders were going wheat-free (good-bye pasta and bread) because gluten, a protein in wheat grain, might interfere with digestion, performance-minded cyclists of all levels started ditching the stuff.

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While Lim's squad swapped their wheat-based noodles and starches for healthy gluten-free grains like rice, oats, and quinoa, many everyday riders simply stocked up on commercially altered gluten-free foods such as scones, cookies, and breads. "These are highly processed foods filled with gums, additives, and processed grains, which aren't any better for you," says Sims.  

There certainly are legitimate reasons to give up gluten. Some people have celiac disease, an inability to digest the protein, which leads to gastrointestinal distress; others may have wheat allergies. A doctor can test you for both conditions. Some experts say you can simply have a gluten sensitivity, which may hamper digestion without causing more overt symptoms. The only way to test for that is to stop eating gluten and see how you feel. "Be sure to substitute in unprocessed grains like amaranth and quinoa, not just 'gluten-free' processed foods," says Sims.  

The bottom line is that athletes who have no discernible symptoms likely won't see performance gains from giving up gluten and will miss out on the slow-burning carbs and nutrients in wheat, especially the whole-grain variety. As Marlor says, "It's an important part of an athlete's diet." 

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Better Fuel Efficiency
It's possible to train your body to burn fat during exercise—and preserve your stored glycogen. Here's how:

Your body burns carbs during exercise. It also burns fat, which is preferable because you always have plenty of that hanging around, even when your stored glycogen is dwindling. And as you become fitter, you become a better fat burner because your body has adapted to let you use more oxygen—and stay in an aerobic fat-burning zone—at higher exercise intensities.

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Beyond that, some experts say you can teach your body to choose fat as its primary fuel source, allowing you to spare your precious glycogen stores. Research suggests that training in a glycogen-depleted state (several hours after your last meal) can trigger cellular changes and increase the production of key enzymes that make you a better fat burner. Those same studies haven't shown much in the way of performance improvement, however. In other words, the adaptations don't seem to make cyclists any faster. 

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Still, under the right circumstances, this approach might be useful. "I use this training method in the off-season to cut body fat," says Marlor. "I'll do two high-intensity morning workouts a week in a glycogen-depleted state. But I keep those sessions to about an hour in length. Afterward, I'll have some carbs for recovery." Jeukendrup also believes in occasional glycogen-depleted training sessions. "This way," he says, "you're training both your fat-burning and carbohydrate-burning systems." 

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But Cavemen Didn't Eat Grains

Let's say you want to take your everyday diet back to the Stone Age and subsist on lean meats, fruits, and vegetables (no grains, legumes, or dairy) for most meals, as advocated by the popular Paleo diet. The fact is, you cannot perform at a high level without the fast-acting carbohydrates that high-carb foods provide. Even the diet's creators recognize this.

In their book The Paleo Diet for Athletes, authors Loren Cordain and Joe Friel concede that endurance athletes need to "bend the rules" and eat "nonoptimal foods" such as bread, pasta, bagels, rice, corn, and other items rich in glucose to fuel their efforts and promote full recovery, before, during, and after exercise. As with most of these diets, you'll still wind up eating less processed crap. "If you eat 'clean' and low on the food chain," says Sims, "your body is going to respond well."

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Your Daily Carbs 

Just as you wouldn't buy a bunch of perishable food before leaving on a vacation, you don't need to consume hundreds of grams of carbs if you're doing nothing more strenuous than tapping a keyboard. Sims recommends these guidelines for matching your overall daily carb intake to how much activity you do. Each gram of carbohydrate provides four calories of energy.

Exercise level: Low/easy
Recommended daily carbohydrate*: 205 to 275 grams (less than 1 hour a day) 

Exercise level: Moderate
Recommended daily carbohydrate: 275 to 340 grams (about 1 hour a day)

Exercise level: Very active
Recommended daily carbohydrate: 410 to 475 grams (1 to 3 hours a day)

Exercise level: Extremely active
Recommended daily carbohydrate: 545 to 580 grams (4 to 5 hours a day or more)

*For a 150-pound cyclist

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