Carbohydrate loading, commonly referred to as carb-loading, or carbo-loading, is a strategy used by endurance athletes, such as

marathon The marathon is a long-distance foot race with a distance of , usually run as a road race, but the distance can be covered on trail routes. The marathon can be completed by running or with a run/walk strategy. There are also wheelchair div ...

ers and triathletes, to maximize the storage of

glycogen Glycogen is a multibranched polysaccharide of glucose that serves as a form of energy storage in animals, fungi, and bacteria. The polysaccharide structure represents the main storage form of glucose in the body. Glycogen functions as one o ...

(or energy) in the muscles and liver. Carbohydrate loading is generally recommended for endurance events lasting longer than 90 minutes. Foods with low glycemic indices are generally preferred for carbo-loading due to their minimal effect on serum glucose levels. Low glycemic foods commonly include vegetables, whole wheat pasta, and grains. Many endurance athletes have large pasta dinners the night before an event. Since muscles also use amino acids extensively when functioning within aerobic limits, meals should also include adequate protein. Large portions before a race can, however, decrease race-day performance if the digestive system has not had the time to process the food regimen.

Without depletion

Research in the 1980s led to a modified carbo-loading regimen that eliminates the depletion phase, instead calling for increased carbohydrate intake (to about 70% of total calories) and decreased training for three days before the event.

Short workout

A new carbo-loading regimen developed by scientists at the

University of Western Australia The University of Western Australia (UWA) is a public research university in the Australian state of Western Australia. The university's main campus is in Perth, the state capital, with a secondary campus in Albany, Western Australia, Albany an ...

calls for a normal diet with light training until the day before the race. On the day before the race, the athlete performs a very short, extremely high-intensity workout (such as a few minutes of sprinting) then consumes of carbohydrate per kilogram of lean mass over the next 24 hours. The regimen resulted in a 90% increase in glycogen storage when compared to before the carbo-load, which is comparable to or higher than the results achieved with other 2 day – 6 day carbo-loading regimes.

Transient hypoglycemia

Carbohydrate ingestion within 2 hours before aerobic exercise triggers elevated levels of insulin in the blood which may dramatically decrease serum glucose levels. This can limit aerobic performance, especially in events lasting longer than 60 minutes. This is known as transient or

reactive hypoglycemia Reactive hypoglycemia, postprandial hypoglycemia, or sugar crash is a term describing recurrent episodes of symptomatic hypoglycemia occurring within four hours"Hypoglycemia." It can also be referred to as "sugar crash" or "glucose crash." Nati ...

, and can be a limiting factor in elite athletes. Individuals susceptible to hypoglycemia are especially at risk for elevated insulin responses and thus will likely suffer from performance-limiting transient hypoglycemia if they do not follow the correct regimen.

Diet composition

The composition of carbohydrates in the athlete's diet during carbohydrate loading is as important as their share of the overall caloric regimen . Most dietary carbohydrates consist of varying proportions of two simple sugars,

glucose Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, using ...

and

fructose Fructose, or fruit sugar, is a Ketose, ketonic monosaccharide, simple sugar found in many plants, where it is often bonded to glucose to form the disaccharide sucrose. It is one of the three dietary monosaccharides, along with glucose and galacto ...

. Fructose may be metabolized into

liver The liver is a major Organ (anatomy), organ only found in vertebrates which performs many essential biological functions such as detoxification of the organism, and the Protein biosynthesis, synthesis of proteins and biochemicals necessary for ...

, but it is ineffective at raising muscle glycogen levels (which is the objective of carbohydrate loading). Consequently, sources of high-fructose carbohydrates, such as fruit and sugar-based foods, are less than optimal for the task. The classic carb-loading meal is

pasta Pasta (, ; ) is a type of food typically made from an unleavened dough of wheat flour mixed with water or eggs, and formed into sheets or other shapes, then cooked by boiling or baking. Rice flour, or legumes such as beans or lentils, are som ...

, whose caloric content is primarily due to

starch Starch or amylum is a polymeric carbohydrate consisting of numerous glucose units joined by glycosidic bonds. This polysaccharide is produced by most green plants for energy storage. Worldwide, it is the most common carbohydrate in human diets ...

, a polymer of glucose. Other high-starch meals which include

bread Bread is a staple food prepared from a dough of flour (usually wheat) and water, usually by baking. Throughout recorded history and around the world, it has been an important part of many cultures' diet. It is one of the oldest human-made f ...

rice Rice is the seed of the grass species ''Oryza sativa'' (Asian rice) or less commonly ''Oryza glaberrima ''Oryza glaberrima'', commonly known as African rice, is one of the two domesticated rice species. It was first domesticated and grown i ...

, and

potatoes The potato is a starchy food, a tuber of the plant ''Solanum tuberosum'' and is a root vegetable native to the Americas. The plant is a perennial in the nightshade family Solanaceae. Wild potato species can be found from the southern United ...

are also part of the correct regimen.

Without depletion

Short workout

Transient hypoglycemia

Diet composition

References

Further reading