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Carbohydrate-loading diet
By Mayo Clinic staffDefinition
A carbohydrate-loading diet (or carb-loading diet) involves increasing the amount of carbohydrates you eat and decreasing your activity several days before a high-intensity-endurance athletic event. Carbohydrate loading helps maximize energy (glycogen) storage and boost your athletic performance.
Purpose
Carbohydrate loading is primarily beneficial if you're an endurance athlete — such as marathon runner, swimmer or cyclist — preparing for a high-intensity competition that will last 90 minutes or more. Carbohydrate loading may help you maximize energy storage for better endurance and delayed fatigue.
Carbohydrate loading isn't necessary for shorter activities such as recreational biking or swimming, weightlifting, and five- or 10-kilometer runs.
Diet details
The role of carbohydrates
Carbohydrates are found in grains, dairy products, fruits, vegetables and legumes (beans and peas). They're also found in sugar and sweets.
Carbohydrates are your body's primary source of energy. During digestion, your body converts carbohydrates into sugar. The sugar enters your bloodstream, where it's transferred to individual cells to provide energy. Some of the extra sugar is stored in your liver and muscles as glycogen.
Increase your energy storage
Your muscles normally store only small amounts of glycogen — enough to support you during recreational exercise activities. But depending on your level of fitness, your muscles may run out of glycogen if you exercise intensely for more than 90 minutes. In turn, your stamina and performance may suffer. This can be an issue during activities such as long-distance running, swimming and cycling, soccer, and triathlons.
Enter carbohydrate loading, a performance-enhancing strategy. Traditionally, carbohydrate loading is done in two steps the week before a high-endurance activity:
- Step 1. About a week before the event, reduce or maintain your carbohydrate intake at about 50 to 55 percent of your total calories. Increase protein and fat intake to compensate for any decrease in carbohydrates. Continue training at your normal level. This helps deplete your carbohydrate stores and make room for the loading that comes next.
- Step 2. Three to four days before the event, increase your carbohydrate intake to 70 percent of your daily calories — or about 4.5 grams of carbohydrates per pound of body weight. Cut back on foods higher in fat to compensate for the extra carbohydrate-rich foods. Also scale back your training to avoid depleting your glycogen stores. Rest completely for a day before the event.
Stephen DeBoer, a marathon runner and registered dietitian at Mayo Clinic, Rochester, Minn., suggests this sample carbohydrate-loading meal plan for an athlete who weighs 170 pounds (77 kilograms). Based on 4 grams of carbohydrates per pound (kilogram) of body weight, it consists of about 70 percent carbohydrates.
| Item (amount) | Carbohydrates (grams) | Calories |
|---|---|---|
| Breakfast | ||
| Milk, fat-free (12 ounces) | 18 | 129 |
| Nutty barley cereal (1 cup) | 92 | 413 |
| 1 cinnamon raisin bagel (3 1/2-inch diameter) | 39 | 194 |
| Reduced-calorie margarine (1 tablespoon) | 0 | 51 |
| Morning snack | ||
| 1 granola bar with oats, sugar, raisins and coconut (1 1/2 ounces total) | 29 | 200 |
| Grape juice, unsweetened (12 ounces) | 56 | 228 |
| Carrots, baby (12) | 10 | 48 |
| Lunch | ||
| Milk, fat-free (8 ounces) | 12 | 86 |
| 4 slices whole-wheat bread (1 1/2 ounces per slice) | 81 | 450 |
| Chicken breast, roasted without skin (3 ounces) | 0 | 142 |
| Romaine lettuce, shredded (1/4 cup) | 1 | 2 |
| Mayonnaise-type salad dressing (2 tablespoons) | 7 | 76 |
| Tortilla chips, low-fat, baked (1 ounce) | 23 | 118 |
| Afternoon snack | ||
| Low-fat fruit yogurt (8 ounces) | 47 | 250 |
| Wheat crackers (10) | 13 | 90 |
| Apple, small (1) | 21 | 77 |
| Cranberry juice (12 ounces) | 46 | 174 |
| Dinner | ||
| Salmon, baked (3 ounces) | 0 | 175 |
| Brown rice (1 1/2 cups) | 67 | 324 |
| Broccoli, steamed (1 cup) | 11 | 54 |
| Milk, fat-free (8 ounces) | 12 | 86 |
| Lettuce salad with tomatoes and carrots (1 1/4 cups) | 3 | 16 |
| Fat-free Italian salad dressing (2 tablespoons) | 2 | 14 |
| Walnuts (1/4 cup) | 4 | 191 |
| Evening snack | ||
| Banana, medium (1) | 27 | 105 |
| Fig bars (2) | 23 | 112 |
| Frozen yogurt, fat-free — chocolate (1 1/2 cups) | 55 | 299 |
| Total | 699 | 4,104 |
Results
If you're a man, a carbohydrate-loading diet can increase the levels of glycogen stored in your muscles by up to two times your normal amount. However, carbohydrate loading may not be as effective if you're a woman. Fewer studies of carbohydrate loading in women exist, and they've yielded unclear results. Women may need to consume a greater percentage of calories from carbohydrates during carbohydrate loading to get the same benefits, and the menstrual cycle also may play a role, but more research is needed.
Even if you've loaded up on carbohydrates ahead of time, you still need to replenish them during the event to maintain your blood sugar levels — especially if you've been going for more than 60 minutes. Try a piece of fruit or a sports drink.
Risks
Carbohydrate loading isn't right for every endurance athlete. Side effects may include:
- Weight gain. Much of this weight is extra water — but if it hampers your performance, you're probably better off skipping the extra carbs.
- Digestive discomfort. You may need to avoid or limit some high-fiber foods one or two days before your event. Beans, bran and broccoli can cause gassy cramps, bloating and loose stools when you're loading up on carbohydrates.
- Blood sugar changes. Carbohydrate loading can affect your blood sugar levels. It's a good idea to consult your doctor or a registered dietitian before you start carbohydrate loading, especially if you have diabetes.
- Body composition and nutrition for sport. In: Wilmore JH, et al. Physiology of Sport and Exercise. 4th ed. Champaign, Ill.: Human Kinetics; 2008:316-353.
- Sedlock DA. The latest on carbohydrate loading: A practical approach. Current Sports Medicine Reports. 2008;7(4):209-213.
- Questions most frequently asked about sports nutrition. President's Council on Physical Fitness and Sports. http://www.fitness.gov/faq.html. Accessed Aug. 23, 2008.
- Carbohydrates. Centers for Disease Control and Prevention. http://www.cdc.gov/nccdphp/dnpa/nutrition/nutrition_for_everyone/basics/carbohydrates.htm. Accessed Aug. 23, 2008.
- USDA National Nutrient Database for Standard Reference, Release 20. U.S. Department of Agriculture. http://www.nal.usda.gov/fnic/foodcomp/search/. Accessed Oct. 24, 2008.
- DeBoer S (expert opinion). Mayo Clinic, Rochester, Minn. Oct. 27, 2008.
