Mayo Clinic Health Library

Carbohydrate-loading diet

Updated: 11-07-2018

Definition

A carbohydrate-loading diet, also called a carb-loading diet, is a strategy to improve your athletic performance for endurance events by increasing the amount of fuel stored in your muscles.

Carbohydrate loading occurs when you eat a high-carbohydrate "training diet" at the same time that you scale back your activity level in the days before an event.

Purpose

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 you need to complete an endurance event with less fatigue, improving your athletic performance.

Carbohydrate loading may be most beneficial if you're an endurance athlete — such as a marathon runner, swimmer, cyclist or all three — preparing for an event that will last 90 minutes or more. Other athletes generally don't need carbohydrate loading. It's usually enough to get about half of your calories from carbohydrates.

Diet details

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 more energy in your muscles. This may give you the stamina to make it through longer endurance events. But, you'll still need to consume some energy sources during your event.

Carbohydrate loading

Carbohydrate loading is done the week before a high-endurance activity. One to three days before the event, increase your carbohydrate intake to about 8 to 12 grams of carbohydrate per kilogram of body weight. Cut back on foods higher in fat to compensate for the extra carbohydrate-rich foods.

Also scale back your training for three to four days before the event. The combination of eating more carbohydrates and tapering activity appear to boost 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 body weight daily is right for general training. (Note that 1 kilogram equals 2.2 pounds.) Endurance athletes may need up to 12 grams per kilogram.

Sample carbohydrate-loading meal plan

Here's a sample carbohydrate-loading meal plan for an athlete who weighs 170 pounds (77 kilograms). It's based on 4.5 grams of carbohydrates for each pound (10 grams per kilogram) of body weight.

You can tweak this sample carbohydrate-loading meal plan to suit your own tastes and nutritional needs.

Sample carbohydrate-loading meal plan
Item (amount) Carbohydrates (grams) Total calories
Breakfast
Milk, fat-free (12 ounces) 18 125
1 plain bagel (4.2 ounces) 52 260
Peanut butter, smooth (2 tablespoons) 7 191
Honey (2 tablespoons) 35 128
Banana (1 medium) 27 105
Morning snack
Crunchy raisin and almond cereal (1 cup) 74 360
Grape juice (12 ounces) 55 225
Lunch
Milk, chocolate, reduced fat (12 ounces) 46 285
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) 0.5 2
Red tomato slices (1/2 cup) 2 11
Mayonnaise, light (2 tablespoons) 3 71
Tortilla chips, low-fat, baked (1 ounce) 23 118
Baby carrots (12) 10 42
Afternoon snack
Low-fat fruit yogurt (8 ounces) 47 250
Low-fat fruit granola (1/2 cup) 33 157
Blueberries (1 cup) 21 83
Cranberry juice, unsweetened (12 ounces) 42 156
Dinner
Wild Atlantic salmon, baked (3 ounces) 0 155
Dinner roll, whole wheat (2 rolls, 1 ounce each) 29 151
Milk, fat-free (12 ounces) 18 125
Salad, combine:
-Romaine lettuce, shredded (2 cups)
3 16
-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
Evening snack
Strawberries (1 cup) 11 46
Sherbet, any flavor (1 1/2 cups) 78 416
Total 754.5 4,543

Source: Nutritionist Pro, 2018

Results

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.

For men, a carbohydrate-loading diet can increase the levels of glycogen stored in the muscles as much as 100 percent of your normal amount. Women may need to consume more calories than usual during carbohydrate loading to get the same benefits as men do.

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 every hour or two. And don't forget to eat carbohydrate-rich foods after your endurance event, too, to replenish your glycogen stores.

Risks

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:

  • 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.