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Does Carb-Loading Really Work?

June 11, 2014
Laura Skladzinski

We’ve heard about distance runners loading up at pasta parties — and it’s not just because they want to fall into a food coma to get a good night’s sleep. Carbohydrate-loading — aka “carb-loading” — before an event can give us more energy during an intense workout by increasing the amount of glycogen, or stored glucose, in muscles. But there’s more to maximizing performance than just scarfing spaghetti the night before the race.

Pasta and Performance — The Need-to-Know

During exercise, our muscles and liver use glycogen, or stored glucose, for energy. While the body gets glucose from most food groups, it converts carbs to glucose more easily than it converts fat or protein, so loading up on carbs can mean a big energy boost. Carb loading is all about upping the amount of glycogen in the body and helps us go longer before hitting “the wall,” or the point when carbohydrate reserves are so depleted that a person can’t reach their highest level of performance.

Carb loading is only necessary for exercise that lasts 90 minutes or more, since that’s when the body starts running low on glycogen. And while we usually hear about carb loading in reference to endurance events like marathons, going carb-wild can also be useful for other types of prolonged high-intensity exercise, like hiking, swimming, or one of those crazy 90-minute spin classes. Carb-ing up may even be useful before weightlifting sessions: One study found that carb loading before lifting increased the amount athletes were able to lift and gave them more time before they felt exhausted. On the other hand, another study didn’t find any difference in lifters’ power output after carb loading, possibly because the participants weren’t lifting long enough to reach exhaustion. But for weightlifters and endurance athletes alike, careful planning is key to carb-loading.

Load Up — Your Action Plan

It’s rarely a good idea to carb-load for the first time the week before a race, so start a carb-loading regimen during training or try carb-loading before a smaller-scale athletic event. (For example, if training for a marathon, test out carb-loading before a half-marathon.) Endurance athletes often start their carb-loading session by keeping carbs to a minimum. During training, a lower-carb, higher-fat diet can help train the body to use fat for energy and reduce its dependence on carbohydrates. Even for athletes who don’t use a low carb diet in training, the carb-loading process should kick off with the depletion of glycogen stores via a low-carb diet for two days (sayonara, sushi rolls!) plus some intense exercise to wipe out the glycogen that’s already in the tanks.

Within 24 hours of the depeletion of glycogen reserves, the muscles begin to rebuild their stores, and over the next few days can actually store glycogen at above-normal capacity. To take advantage of muscles’ increased glycogen-storage capacity, about three days before the athletic event, begin a loading period (see details below) of increased carbohydrate intake. (Bring on the bagels!) And once race day hits it still might not be time to stop — eating carbs during exercise can also help replenish glycogen stores even while we’re simultaneously burning that glycogen for energy. That said, it’s important to remember that carb-loading doesn’t mean overeating.

For a successful carb-loading plan, follow these Greatist tips.

Chowing Down: How to Carb-Load

  • When to eat: When approaching a peak endurance performance day (like a race), do a high-intensity workout three to four days before the race to clear out glycogen stores. Then it’s time to hit the cereal aisle in the supermarket and immediately increase carbohydrate intake. 
  • What to eat: Just before game day, the goal of carb-loading is to increase carbohydrate intake relative to the intake of proteins and fats — carbs should comprise between 63 and 81 percent of total calories. As for mid-workout fuel, It may be tempting to stock up on expensive “performance gels,” but multiple studies have found no difference in performance from loading up on natural carb sources (like sun-dried raisins) compared to the manufactured stuff. Sports drinks can also help fill up muscles and don’t require cutlery or chewing — look for those that contain a mix of carbohydrates (e.g., dextrose, fructose, and maltodextrin) in the ingredients list.
  • How much to eat: Nutritional requirements during carb loading depend on the individual person and the type of training. In general, endurance athletes should consume about four grams of carbohydrates per day for each pound of body weight. (For a 150-pound person, that means two cups of cereal, one banana, four pieces of bread, and four cups of pasta, or any combination of foods that comes out to 600 grams of carbs.) It’s important to keep calories consistent with normal eating habits in order to avoid weight gain. The key is to increase the ratio of carbs to proteins and fats, and not to increase total caloric intake. (Increasing body weight can hinder performance even more than skimping on carbs!) 

Caution: Carb Crossing

Before embarking on a carb-loading bonanza, keep in mind a few notes of caution:

  • Take hormones into account. Changes in women’s menstrual cycles can affect not just overall performance but also the effectiveness of carb loading. During the follicular phase, which begins the day after your period stops and lasts for two weeks, researchers found carb-loading didn’t actually improve performance. If possible, try to time races to fall in the luteal phase, or days 14 through 28.
  • Manage fiber intake. Some high-carbohydrate foods may get their carbs from fiber, which can contribute to bathroom issues and causes fullness by absorbing fluid that your body needs to perform. Try to keep fiber levels consistent with what you’ve eaten during training to avoid any mid-race pit-stops or uncomfortable tummy aches and bloating. (The miles only seem to go by slower when you’re desperate for a porta potty!)
  • Watch out for weight gain. No matter how you try to justify it as “a race necessity” (we’ve been there!), excess eating is just that, and can quickly lead to weight gain. While athletes like Michael Phelps can supposedly eat 12,000 calories a day, someone with a lower-intensity training schedule or someone who’s trying to lose weight will need to eat a lot less. There are complicated calculations to help figure out the right amount of carbs for each person; for the mathematically challenged, simply experiment to see what’s right for you and your body. However, note that glycogen gains come with water retention of three to four times normal levels — so don’t be afraid of a bit of extra water weight on race day.
  • Balance blood sugar levels. A spike in blood sugar can result from eating high-glycemic, sugary carbs (like white potatoes, un-enriched pasta, and white bread). To avoid the spike and slump, combine carbs with fat and protein and eat carbs that vary on the GI scale — those combinations will give you a nice kick at the start but also provide a slow burn of energy to get you through the race. Sweet potatoes are one option for carbs that provide lasting energy. And one favorite pre-race breakfast: wheat toast (low GI) with peanut butter and a sliced banana (high GI).

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