Medically reviewed on February 24, 2018.
A carbohydrate-loading diet, also called a carb-loading diet, is a strategy to increase the amount of fuel stored in your muscles to improve your athletic performance for endurance events.
Carbohydrate loading is a result of continuing to eat a high-carbohydrate "training diet" while scaling back your activity level during carbohydrate loading.
Any physical activity requires carbohydrates for fuel. For most recreational activity, your body uses its existing energy stores for fuel. But when you engage in long, intense athletic events, your body needs extra energy to keep going. The purpose of carbohydrate loading is to give you the energy to complete an endurance event with less fatigue, improving your athletic performance.
Carbohydrate loading is most beneficial if you're an endurance athlete — such as a marathon runner, swimmer or cyclist — preparing for an event that will last 90 minutes or more. Other athletes generally don't need carbohydrate loading. It's enough to get half or more of your calories from carbohydrates.
The role of carbohydrates
Carbohydrates, also known as starches and sugars, are your body's main energy source. Complex carbohydrates include legumes, grains and starchy vegetables, such as potatoes, peas and corn. Simple carbohydrates are found mainly in fruits and milk, as well as in foods made with sugar, such as candy and other sweets.
During digestion, your body breaks down carbohydrates into sugar. The sugar enters your bloodstream, where it's then transferred to individual cells to provide energy. Sugar is stored in your liver and muscles as glycogen — your energy source.
Increase your energy storage
Your muscles normally store only small amounts of glycogen — enough to support you during recreational exercise activities. If you exercise intensely for more than 90 minutes, your muscles may run out of glycogen. At that point, fatigue might set in, and your performance may suffer.
But with carbohydrate loading, you may be able to store up more energy in your muscles to give you the stamina to make it through longer endurance events. You still will need to consume some energy sources during your event.
Carbohydrate loading is done the week before a high-endurance activity:
Three to four days before the event, increase your carbohydrate intake to about 10 to 12 grams of carbohydrate per kilogram of body weight (70 percent of your daily calories). Cut back on foods higher in fat to compensate for the extra carbohydrate-rich foods.
Also scale back your training. Rest completely the day before your big event. The combination of eating more carbohydrates and tapering activity appear to improve muscle glycogen stores.
How many carbs you need depends on your total calorie goal as well as your sport. For most athletes, 5 to 7 grams of carbohydrate per kilogram of weight daily is right for general training. However, endurance athletes may need up to 12 grams per kilogram (1 kilogram equals 2.2 pounds).
Sample carbohydrate-loading meal plan
Here's a sample carbohydrate-loading meal plan for an athlete who weighs 170 pounds (77 kilograms). Based on 4.5 grams of carbohydrates for each pound (10 grams per kilogram) of body weight, the meal plan consists of about 70 percent carbohydrates. You can tweak this sample carbohydrate-loading meal plan to suit your own tastes and nutritional needs. Keep in mind that 1 gram of carbohydrates has 4 calories.
|Sample carbohydrate-loading meal plan|
|Item (amount)||Carbohydrates (grams)||Total calories|
|Milk, fat-free (12 ounces)||18||125|
|1 plain bagel||52||260|
|Peanut butter, smooth (2 tablespoons)||7||191|
|Honey (2 tablespoons)||35||128|
|Crunchy raisin and almond cereal (1 cup)||74||360|
|Grape juice (12 ounces)||55||225|
|Milk, chocolate, reduced fat (12 ounces)||45||285|
|4 slices white bread (1 ounce per slice)||49||266|
|Chicken breast, roasted without skin (4 ounces or 1/2 breast)||0||187|
|Romaine lettuce, shredded (1/4 cup)||1||2|
|Red tomato slices (1/2)||2||11|
|Mayonnaise, light (2 tablespoons)||3||71|
|Tortilla chips, low-fat, baked (1 ounce)||23||118|
|Baby carrots (12)||10||42|
|Low-fat fruit yogurt (8 ounces)||47||249|
|Low-fat fruit granola (1/2 cup)||33||157|
|Blueberries (1 cup)||21||83|
|Cranberry juice, unsweetened (12 ounces)||42||157|
|Wild Atlantic salmon, baked (3 ounces)||0||155|
|Dinner roll, whole wheat (2)||29||151|
|Milk, fat-free (12 ounces)||18||125|
-Romaine lettuce, shredded (2 cups)
|-Bell or sweet green pepper (1/4 cup)||2||7|
|-Green apple, chopped (1 medium)||25||95|
|-Dried cranberries (1/3 cup)||33||130|
|-English walnuts, chopped (1/4 cup)||4||191|
|-Asiago cheese, shredded (1 ounce)||1||134|
|-Reduced-fat Ranch salad dressing (2 tablespoons)||6||55|
|Strawberry slices (1 cup)||11||46|
|Sherbet, any flavor (1 1/2 cups)||88||417|
Source: Nutritionist Pro, 2015
Carbohydrate loading may give you more energy during an endurance event. You may feel less fatigued and see an improvement in your performance after carbohydrate loading. But carbohydrate loading isn't effective for everyone.
Other factors can influence your athletic performance or interfere with the effectiveness of your carbohydrate-loading strategy, including how fit you are, how well you hydrate and how intensely you exercise. Even with carbohydrate loading, you still may feel muscle fatigue.
If you're a man, a carbohydrate-loading diet can increase the levels of glycogen stored in your muscles from 25 to 100 percent of your normal amount. Fewer research studies exist about carbohydrate loading in women, and they've yielded mixed results. A woman may need to consume more calories than usual during carbohydrate loading to get the same benefits as a man does.
Despite carbohydrate loading, you still need to replenish your body's energy during endurance events to maintain your blood sugar levels. You can do this by periodically consuming sports drinks, gels, or bars, fruit, or hard or chewy candies during your event at the rate of 30 to 60 grams an hour. And don't forget to eat carbohydrate-rich foods after your endurance event, too, to replenish your glycogen stores.
Carbohydrate loading isn't right for every endurance athlete. It's a good idea to consult your doctor or a registered dietitian before you start carbohydrate loading, especially if you have diabetes. You may also need to experiment with different amounts of carbohydrates to find what works best for you.
A carbohydrate-loading diet can cause some discomfort or side effects, such as:
- Weight gain. Much of this weight is extra water, but if it hampers your performance, stick to your training diet rather than carbohydrate loading.
- 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.
- Blood sugar changes. Carbohydrate loading can affect your blood sugar levels. If you have diabetes, monitor your blood sugar during training or practices to see what works best for you. And talk to your dietitian or doctor to make sure your meal plan is safe for you.