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 colorectal 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.
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 Australia 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 12 g 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 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.
- Noblett, S. E.; Watson, D. S.; Huong, H.; Davison, B.; Hainsworth, P. J.; Horgan, A. F. (2006). "Pre-operative oral carbohydrate loading in colorectal surgery: A randomized controlled trial". Colorectal Disease 8 (7): 563–9. doi:10.1111/j.1463-1318.2006.00965.x. PMID 16919107.
- Jensen, Christopher D. "Carbohydrate Loading".[unreliable medical source?]
- Martini, Frederic H.; Timmons, Michael J.; Tallitsch, Robert B. (2008). Human Anatomy (6th ed.). Benjamin Cummings. p. 292. ISBN 978-0-321-50042-7.
- Fitzgerald, Matt. "The Evolving Art of Carbo-Loading".[unreliable medical source?]
- Peterson, David. "The Science of Carbohydrate Loading".[unreliable medical source?]
Further reading 
- Wax, Benjamin; Brown, Stanley P; Webb, Heather E; Kavazis, Andreas N; Kinzey, Steve (2011). "Effects of Carbohydrate Supplementation on Force Output and Time to Exhaustion during Static Leg Contractions Superimposed with Electromyostimulation". Journal of Strength and Conditioning Research: 1. doi:10.1519/JSC.0b013e318234ec0e. PMID 21912287.
- Hawley, John A.; Schabort, Elske J.; Noakes, Timothy D.; Dennis, Steven C. (1997). "Carbohydrate-Loading and Exercise Performance". Sports Medicine 24 (2): 73–81. doi:10.2165/00007256-199724020-00001. PMID 9291549.
- Sedlock, Darlene A. (2008). "The Latest on Carbohydrate Loading: A Practical Approach". Current Sports Medicine Reports 7 (4): 209–13. doi:10.1249/JSR.0b013e31817ef9cb. PMID 18607222.
- Burke, Louise M.; Millet, Gregoire; Tarnopolsky, Mark A.; International Association of Athletics Federations (2007). "Nutrition for distance events". Journal of Sports Sciences 25: S29–38. doi:10.1080/02640410701607239. PMID 18049981.
- Bentley, David J.; Cox, Gregory R.; Green, Daniel; Laursen, Paul B. (2008). "Maximising performance in triathlon: Applied physiological and nutritional aspects of elite and non-elite competitions". Journal of Science and Medicine in Sport 11 (4): 407–16. doi:10.1016/j.jsams.2007.07.010. PMID 17869183.
- Hatfield, Disa L.; Kraemer, William J.; Volek, Jeff S.; Rubin, Martyn R.; Grebien, Bianca; Gómez, Ana L.; French, Duncan N.; Scheett, Timothy P. et al. (2006). "The Effects of Carbohydrate Loading on Repetitive Jump Squat Power Performance". The Journal of Strength and Conditioning Research 20 (1): 167–71. doi:10.1519/R-18300.1. PMID 16503677.
- Havemann, L.; West, SJ; Goedecke, JH; MacDonald, IA; St Clair Gibson, A; Noakes, TD; Lambert, EV (2006). "Fat adaptation followed by carbohydrate loading compromises high-intensity sprint performance". Journal of Applied Physiology 100 (1): 194–202. doi:10.1152/japplphysiol.00813.2005. PMID 16141377.
- Andrews, Jessica L.; Sedlock, Darlene A.; Flynn, Michael G.; Navalta, James W.; Ji, Hongguang (2003). "Carbohydrate loading and supplementation in endurance-trained women runners". Journal of Applied Physiology 95 (2): 584–90. doi:10.1152/japplphysiol.00855.2002. PMID 12716874.
- Bussau, Vanessa; Fairchild, Timothy; Rao, Arjun; Steele, Peter; Fournier, Paul (2002). "Carbohydrate loading in human muscle: An improved 1 day protocol". European Journal of Applied Physiology 87 (3): 290–5. doi:10.1007/s00421-002-0621-5. PMID 12111292.