Carbohydrate loading
Encyclopedia
Carbohydrate loading, commonly referred to as carbo-loading or carb-loading, is a strategy used by endurance athletes, such as marathon runners, to maximize the storage of glycogen
(or energy) in the muscles.
Carbohydrate loading is also used in healthcare to optimise the condition of patients prior to surgery.
Carbohydrate loading is generally recommended for endurance events lasting longer than 90 minutes. For many endurance athletes the foods of choice for carbo-loading are those of low glycemic indices
due to their minimal effect on serum glucose levels. Low glycemic foods commonly include fruits, vegetables, whole wheat pasta and grains. Because of this, many marathoners and triathlon
participants have large pasta dinners the night before the race. Since muscles also extensively utilize amino acids when functioning within aerobic limits, meals should include adequate protein on top of carbohydrates. Large portions before a race can, however, be detrimental to race-day performance if the digestive system has not had the time to adequately process the food.
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 reportedly resulted in a 90% increase in glycogen storage.
Most dietary carbohydrates consist of varying proportions of two simple sugars, glucose
and fructose
. Fructose may be metabolized into liver
glycogen
, 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 sweets, are less than optimal for the task. The classic carb-loading meal is pasta
, whose caloric content is primarily due to starch
, a glucose polymer. Other high-glucose meals include bread
, rice
, and potatoes.
Glycogen
Glycogen is a molecule that serves as the secondary long-term energy storage in animal and fungal cells, with the primary energy stores being held in adipose tissue...
(or energy) in the muscles.
Carbohydrate loading is also used in healthcare to optimise the condition of patients prior to surgery.
Carbohydrate loading is generally recommended for endurance events lasting longer than 90 minutes. For many endurance athletes the foods of choice for carbo-loading are those of low glycemic indices
Glycemic index
The glycemic index, glycaemic index, or GI is a measure of the effects of carbohydrates on blood sugar levels. Carbohydrates that break down quickly during digestion and release glucose rapidly into the bloodstream have a high GI; carbohydrates that break down more slowly, releasing glucose more...
due to their minimal effect on serum glucose levels. Low glycemic foods commonly include fruits, vegetables, whole wheat pasta and grains. Because of this, many marathoners and triathlon
Triathlon
A triathlon is a multi-sport event involving the completion of three continuous and sequential endurance events. While many variations of the sport exist, triathlon, in its most popular form, involves swimming, cycling, and running in immediate succession over various distances...
participants have large pasta dinners the night before the race. Since muscles also extensively utilize amino acids when functioning within aerobic limits, meals should include adequate protein on top of carbohydrates. Large portions before a race can, however, be detrimental to race-day performance if the digestive system has not had the time to adequately process the food.
Without depletion
In the 1980s, research 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 prior to the event. Most athletes now follow this modified regimen; it is recommended by many coaches, although there are some athletes who still follow the original carbo-loading regimen.Short workout
A new carbo-loading regimen developed by scientists at the University of Western AustraliaUniversity of Western Australia
The University of Western Australia was established by an Act of the Western Australian Parliament in February 1911, and began teaching students for the first time in 1913. It is the oldest university in the state of Western Australia and the only university in the state to be a member of the...
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 reportedly resulted in a 90% increase in glycogen storage.
Transient hypoglycemia
Carbohydrate ingestion less than 2 hours prior to 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, 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.Diet composition
The composition of carbohydrates in the athlete's diet during carbohydrate loading is as important as their share of the overall caloric intake.Most dietary carbohydrates consist of varying proportions of two simple sugars, glucose
Glucose
Glucose is a simple sugar and an important carbohydrate in biology. Cells use it as the primary source of energy and a metabolic intermediate...
and fructose
Fructose
Fructose, or fruit sugar, is a simple monosaccharide found in many plants. It is one of the three dietary monosaccharides, along with glucose and galactose, that are absorbed directly into the bloodstream during digestion. Fructose was discovered by French chemist Augustin-Pierre Dubrunfaut in 1847...
. Fructose may be metabolized into liver
Liver
The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...
glycogen
Glycogen
Glycogen is a molecule that serves as the secondary long-term energy storage in animal and fungal cells, with the primary energy stores being held in adipose tissue...
, 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 sweets, are less than optimal for the task. The classic carb-loading meal is pasta
Pasta
Pasta is a staple food of traditional Italian cuisine, now of worldwide renown. It takes the form of unleavened dough, made in Italy, mostly of durum wheat , water and sometimes eggs. Pasta comes in a variety of different shapes that serve for both decoration and to act as a carrier for the...
, whose caloric content is primarily due to starch
Starch
Starch or amylum is a carbohydrate consisting of a large number of glucose units joined together by glycosidic bonds. This polysaccharide is produced by all green plants as an energy store...
, a glucose polymer. Other high-glucose meals include bread
Bread
Bread is a staple food prepared by cooking a dough of flour and water and often additional ingredients. Doughs are usually baked, but in some cuisines breads are steamed , fried , or baked on an unoiled frying pan . It may be leavened or unleavened...
, rice
Rice
Rice is the seed of the monocot plants Oryza sativa or Oryza glaberrima . As a cereal grain, it is the most important staple food for a large part of the world's human population, especially in East Asia, Southeast Asia, South Asia, the Middle East, and the West Indies...
, and potatoes.