Carbohydrate-loading diet

Definition

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.