Before becoming a dietitian, I was always skeptical of the pre-race spaghetti dinner. You know how they say Valentine’s Day was created by the greeting card industry to boost sales? I suspected that the pre-race pasta dinner was contrived by Big Noodle to increase spaghetti revenues.
A few years of dietetics school (plus a few endurance races) have shown me the error of my ways. The pasta dinner is not only a delicious way to blow off steam before a race, but it can also boost performance when used as part of a strategic carb load.
Why Carb Load?
Carbohydrates are the body’s preferred fuel source during aerobic activities, like running or cycling.
Dietary carbs are broken down in the body to glucose. Glucose molecules travel through the bloodstream to the body’s cells, which use them for energy. Any glucose that’s not used quickly for energy is converted to glycogen and stored in the liver and the muscles. Blood glucose and glycogen are used for fuel during exercise.
But glycogen is limited. The average person stores 1,600 to 2,500 calories of energy from glycogen. Blood glucose is even more scarce, with only 20 to 100 calories from glucose on average.
Once glycogen stores are used up, the body shifts to stored fats for energy. Fats require much more oxygen to be broken down into fuel. The increased oxygen demands cause the athlete to “hit the wall” or “bonk.”
This takes time, but not as much as you’d think. Workouts longer than 90 minutes increase bonk risk. If you’ve never hit the wall, consider yourself lucky. It’s been known to cause extreme fatigue, brain fog, decreased motivation, dizziness, hallucinations, anxiety and other symptoms.
A solid nutrition plan can help athletes fend off the bonk. One common strategy is glycogen supercompensation (a fancy term for carbohydrate loading). Carb loading is the practice of eating large amounts of carbohydrates in the days leading up to an event in order to increase muscle glycogen stores.
Muscle studies have found carb loading to nearly double muscle glycogen, and to improve performance by about 3 percent — or about 7 minutes for a four-hour marathoner.
So, how does it work? Here are some common myths and facts about carb loading.
Myth: Thou Must Deplete
The classic carb loading protocol began with a glycogen depletion phase beginning six days before an endurance event. Athletes trained hard for three days while consuming a low carb diet. After three days, athletes tapered workouts while increasing carbohydrate intake to 10 grams per carbohydrate per kilogram of body weight per day (that’s about 4.55 grams per pound of body weight, if your metric math is rusty).
Studies have since found it possible to reach comparable muscle glycogen levels without the depletion phase. Newer recommendations involve resting for 36 to 48 hours before an event to prevent muscle glycogen losses. Experts recommend 10 to 12 grams of carbohydrate per kilogram of body weight per day. This would equal about 680 to 816 grams of carbohydrate for an athlete weighing 150 pounds (see graphic).
Myth: All Carbs Are Created Equal
A two-day carb fest sounds pretty fun, right? It’s not always as awesome as it sounds.
For one, some find it difficult to eat the volume of food necessary to properly carb load. Choosing low-fat options may help, as fat delays stomach emptying and promotes fullness. Many athletes find it easier to get sports drink or liquid carb sources down the hatch.
Athletes prone to gastrointestinal distress should choose low-fiber carb sources. Too much fiber may result in diarrhea or cramping on competition day. White bread, white rice, pasta, sports bars and sports drinks are recommended.
It may also be useful to keep a food diary during your carb load, with data about how you performed and how you felt on race day. Doing so can provide insights about what works well for future events.
Myth: Carb Loading is Enough
When done properly, carb loading has been shown to prolong steady-state exercise by roughly 20 percent. But if you bonk around 90 minutes into an event, that only buys you 18 minutes.
Athletes should aim for 1 to 4 grams of carbohydrate per kilogram of body weight, one to four hours before endurance exercise. This helps promote steady blood sugar levels early in the competition.
Additionally, the Academy of Nutrition and Dietetics recommends 30 to 60 grams of carbohydrate per hour for events lasting 1 to 2.5 hours, and up to 90 grams of carb per hour for events 2.5 hours or longer.
Fact: Carb Loading Isn’t Always Right
Carb loading can increase your stamina during endurance sports, but it’s not the right approach for every athlete.
For one, it may not be safe or comfortable for people with certain health conditions. Those with diabetes should always speak with a doctor before adjusting carb intake. And as discussed above, those prone to GI distress may perform better without carb loading (you know, fewer dashes to the Porta John).
Experienced athletes may find carb loading more helpful for certain events than others. Carbs are metabolized more rapidly in hot weather and at altitude, for example. Ken Roberts, a multisport athlete and dietetic intern, carb loads selectively based on training level, weather and other conditions.
“I carb load depending on the event. During very hot weather events such as an Ironman 70.3 or marathon, yes. A cold weather Spartan Beast, no. An Olympic triathlon where the weather is very hot, I will a little bit, but not all the way to 10 grams of carb per kilogram,” Roberts said.
So, how do you know if it’s right for you? As always, test it out before an important competition. Pick a moderate to high-intensity workout lasting 90 minutes or more and carb load for two days prior as described above.
And if you decide it’s not for you, be sure to adequately replenish your carb stores during events, as described above. This will help keep you from hitting the dreaded wall.
Author: Kimberly Yawitz is a registered dietitian and a freelance writer in St. Louis, Mo.
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