Editing Glycogen (section)

==Clinical relevance==

===Disorders of glycogen metabolism===
The most common disease in which glycogen [[metabolism]] becomes abnormal is [[diabetes]], in which, because of abnormal amounts of insulin, liver glycogen can be abnormally accumulated or depleted. Restoration of normal glucose metabolism usually normalizes glycogen metabolism, as well.

In [[hypoglycemia]] caused by excessive insulin, liver glycogen levels are high, but the high insulin levels prevent the [[glycogenolysis]] necessary to maintain normal blood sugar levels. [[Glucagon]] is a common treatment for this type of hypoglycemia.

Various [[inborn errors of carbohydrate metabolism]] are caused by deficiencies of enzymes or transport proteins necessary for glycogen synthesis or breakdown. These are collectively referred to as [[glycogen storage disease]]s.

===Glycogen depletion and endurance exercise===

Long-distance athletes, such as [[Marathon (sport)|marathon]] runners, [[Cross-country skiing|cross-country skiers]], and [[cyclist]]s, often experience glycogen depletion, where almost all of the athlete's glycogen stores are depleted after long periods of exertion without sufficient carbohydrate consumption. This phenomenon is referred to as "[[hitting the wall]]" in running and "bonking" in cycling.

Glycogen depletion can be forestalled in three possible ways:
* First, during exercise, carbohydrates with the highest possible rate of conversion to blood glucose (high [[glycemic index]]) are ingested continuously. The best possible outcome of this strategy replaces about 35% of glucose consumed at heart rates above about 80% of maximum.
* Second, through endurance training adaptations and specialized regimens (e.g. fasting, low-intensity endurance training), the body can condition [[Myocyte#type I anchor|type&nbsp;I muscle]] fibers to improve both fuel use efficiency and workload capacity to increase the percentage of fatty acids used as fuel,<ref>{{cite web |title=Methods of endurance training, Part&nbsp;1 |date=2009-10-30 |url=http://www.bodyrecomposition.com/training/methods-of-endurance-training-part-1.html |access-date=1 August 2013 |archive-date=22 July 2018 |archive-url=https://web.archive.org/web/20180722203112/https://bodyrecomposition.com/training/methods-of-endurance-training-part-1.html/ |url-status=dead}}</ref><ref>{{cite web |title=Steady state vs. tempo training and fat loss |date=2008-06-02 |url=http://www.bodyrecomposition.com/fat-loss/qa-steady-state-vs-tempo-training-and-fat-loss.html |access-date=1 August 2013 |archive-date=5 September 2017 |archive-url=https://web.archive.org/web/20170905054006/https://www.bodyrecomposition.com/fat-loss/qa-steady-state-vs-tempo-training-and-fat-loss.html/ |url-status=dead }}</ref> sparing carbohydrate use from all sources.
* Third, by consuming large quantities of carbohydrates after depleting glycogen stores as a result of exercise or diet, the body can increase storage capacity of intramuscular glycogen stores.<ref name="Jensen 2020"/><ref>{{cite web |last=McDonald |first=Lyle |date=2012-07-25 |title=Research review: An in-depth look into carbing up on the cyclical ketogenic diet |url=http://www.directlyfitness.com/store/carbing-cyclical-ketogenic-diet/ |access-date=19 February 2017 |archive-date=11 November 2020 |archive-url=https://web.archive.org/web/20201111194513/http://www.directlyfitness.com/store/carbing-cyclical-ketogenic-diet/ |url-status=dead }}</ref><ref>{{cite book |last=McDonald |first=Lyle |year=1998 |title=The Ketogenic Diet: A complete guide for the dieter and the practitioner |publisher=Lyle McDonald}}</ref><ref name="pmid5123660">{{cite journal |vauthors=Costill DL, Bowers R, Branam G, Sparks K |date=December 1971 |title=Muscle glycogen utilization during prolonged exercise on successive days |journal=J Appl Physiol |volume=31 |issue=6 |pages=834–838 |pmid=5123660 |doi=10.1152/jappl.1971.31.6.834}}</ref> This process is known as [[carbohydrate loading]]. In general, glycemic index of carbohydrate source does not matter since muscular insulin sensitivity is increased as a result of temporary glycogen depletion.<ref name="pmid3538900">{{cite journal |vauthors=Zorzano A, Balon TW, Goodman MN, Ruderman NB |date=December 1986 |title=Glycogen depletion and increased insulin sensitivity and responsiveness in muscle after exercise |journal=Am. J. Physiol. |volume=251 |issue=6, Part&nbsp;1 |pages=E664–E669 |pmid=3538900 |doi=10.1152/ajpendo.1986.251.6.E664}}</ref><ref>{{cite book |last=McDonald |first=Lyle |year=2003 |title=The Ultimate Diet&nbsp;2.0 |publisher=Lyle McDonald}}</ref>

When athletes ingest both carbohydrate and [[caffeine]] following exhaustive exercise, their glycogen stores tend to be replenished more rapidly;<ref>{{cite journal |last1=Pedersen |first1=D.J. |last2=Lessard |first2=S.J. |last3=Coffey |first3=V.G. |display-authors=etal |date=July 2008 |title=High rates of muscle glycogen resynthesis after exhaustive exercise when carbohydrate is coingested with caffeine |journal=Journal of Applied Physiology |volume=105 |issue=1 |pages=7–13 |pmid=18467543 |doi=10.1152/japplphysiol.01121.2007}}</ref><ref name="Recovery nutrition review">{{cite journal |last1=Beelen |first1=M. |last2=Burke |first2=L.M. |last3=Gibala |first3=M.J. |last4=van&nbsp;Loon |first4=L.J.C. |date=December 2010 |title=Nutritional strategies to promote post-exercise recovery |journal=International Journal of Sport Nutrition and Exercise Metabolism |volume=20 |issue=6 |pages=515–532 |pmid=21116024 |s2cid=13748227 |doi=10.1123/ijsnem.20.6.515}}</ref> however, the minimum dose of caffeine at which there is a [[clinically significant]] effect on glycogen repletion has not been established.<ref name="Recovery nutrition review" />

===Nanomedicine===
Glycogen [[nanoparticle]]s have been investigated as potential [[drug delivery systems]].<ref>{{cite journal |title=Glycogen as a Building Block for Advanced Biological Materials |author1=Quinn A. Besford |author2=Francesca Cavalieri |author3=Frank Caruso |date=7 May 2020 |orig-year=16 October 2019 |journal=Advanced Materials |volume=32 |issue=18 |at=1904625 |doi=10.1002/adma.201904625|pmid=31617264 |bibcode=2020AdM....3204625B |hdl=11343/230737 |s2cid=204738366 |hdl-access=free }}</ref>