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[[File:Gels.JPG|right|thumb|300px|My supply of gels]]Understanding some of the science behind energy gels can help in [[Comparison of Energy Gels| evaluating and choosing the right gel]].=Carbohydrate Absorption =Maltodextrin There are three main components to the ease of absorption of a carbohydrate; how much water needs to be used to dilute it, how fast it gets into the blood and Sugarthe digestive path in the gut.==Required Dilution – Isotonic Drinks==A sport fuel is most easily absorbed when it is isotonicIsotonic drinks have a similar concentration (osmolality) of carbohydrate and electrolytes to the human blood and are easier to absorb<ref> http://jap.physiology.org/cgi/content/full/85name="isotonic"/5/1941 Hypertonic solutions are less easily absorbed</ref>. The word isotonic means that there concentration is based on the same concentration number of molecules in rather than the fuel as in the bloodweight, so an isotonic drink with bigger molecules has more carbohydrate by weight. Most Gels are made from [[Maltodextrin]] (sometime called maltodextrose), which is a long molecule made up that is a chain of linked glucose. Because [[Maltodextrin]] has larger molecules, so you can have a lot of it in an isotonic solution. Most Gels are close to isotonic without any significant dilution. [[Maltodextrin]] is isotonic at 150g /500ml, where fructose, glucose and sucrose (600 Caloriestable sugar)are isotonic at 26g/16 oz or 9g/oz<ref name="malto"/>500ml. Gels are typically 25g/1oz, requiring only an equal quantity of liquid This means that you need to dilute. This can be achieved using by mixing the gel simple sugars with saliva six times as much water as it is consumedMaltodextrin. This makes gels very easily digested==Absorption Rate - Glycemic Index=={{Main|Glycemic Index}}Glycemic index reflects how high a carbohydrate raises the blood sugar level. A metric for how easily carbohydrates are digested * Glucose is the [[standard against which everything else is measured, so it has a Glycemic Index]], which of 100. Glucose is how much used because it raises the blood sugar rises when a food is digested compared with glucosefaster than almost anything else. * [[Maltodextrin| Maltodextrin]] actually has a glycemic index >of over 100, with values between 105 and 136. Note that there are some Gels that are not * [[MaltodextrinFructose| Fructose]] basedhas a low glycemic index of 19, such as it has to go via the old formula Clif Shots use brown rice syrupliver to be converted to glucose. ==Caffeine in GelsDigestive Path==While fructose has a low isotonic concentration and a low glycemic index, it can be absorbed via a different path ([http://en.wikipedia.org/wiki/GLUT5 GLUT5]) to glucose and Maltodextrin ([Caffeinehttp://en.wikipedia.org/wiki/GLUT2 GLUT2]] not only improves performance). This means that if you have enough glucose or Maltodextrin to saturate that absorption path, it also increases adding fructose will improve the overall usage of the absorption carbohydrate intake<ref name="Rowlands-2008"/>. =Ingredient Analysis=Here is an analysis of sugar from the gutmost common ingredients * '''Maltodextrin''' is the best form of carbohydrate, so it will make Gels quicker actingand provides the majority of carbohydrate in many gels. It has little or no flavor. * '''Glucose''' is easily digested, though not quite as easy as Maltodextrin. Glucose is about 74% as sweet as sugar (sucrose)<ref name="Sweetness"/>.* '''Fructose''' is useful as an adjunct to Maltodextrin, but too much Fructose will cause digestive problems in many people. Fructose is 1.7x as sweet as table sugar<ref name=Blood "Sweetness"/>. * '''Sucrose '''(Sugar) is half glucose and half fructose joined together, but these components are split as part of digestion. The word 'sugar' can be used to mean any type of sugar, but in general use it refers to Sucrose. Sometimes manufacturers try to conceal sugar in the ingredients by referring to it as 'evaporated cane juice'. * '''Brown Rice Syrup''' is made by cooking rice with an enzyme to break down the starch. Brown ryce syrup is a mixture of 45% [http://en.wikipedia.org/wiki/Maltose maltose] (2 glucose molecules) and Insulin=52% [http://en.wikipedia.org/wiki/Maltotriose maltotriose] (3 glucose molecules) with 3% as simple glucose. For practical purposes it can be considered the same as glucose, with an estimated Glycemic Index of around 85. However, there are concerns that organic brown rice syrup may be contaminated with arsenic<ref name="JacksonTaylor2012"/>. If you take * '''Fat''' can make a gel or other fast acting carbohydrate more palatable and is a useful fuel source at restultramarathon distances.* '''Protein''' can provide an additional fuel source and help limit the tendency of your body to cannibalize muscle for fuel. * '''Amino acids''' may help performance, your but the evidence is unclear at the levels provided in most gels. * '''[[Caffeine]] '''is great for improving performance and speeding the absorption of carbohydrate. =Reactive Hypoglycemia =In some people their blood sugar will rise drop to lower than normal levels after a high carbohydrate meal, a condition known as Reactive Hypoglycemia<ref name="Brun"/>. This condition effects some athletes who take carbohydrate before exercise<ref name="Kuipers-1999"/>, but not if the carbohydrate is taken during the warm up<ref name="Brouns-1989"/> or immediately before exercise<ref name="Jeukendrup-2010"/>. It appears this hypoglycemia is specific to some individuals<ref name="Moseley-2003"/>. However, there appears to be no performance impact from this hypoglycemia<ref name="Jeukendrup-2010"/> and your pancreas will release insulinI found no reports of hypoglycemia in response to carbohydrate taken during exercise. Immediately after exercise=Isotonic Calculations=For those interested, there is the insulin will cause math behind the isotonic calculations I use on my [[Comparison of Energy Gels| Comparison of Energy Gels]].* Blood has an osmolality of 280-330mOsm/kg, so drinks with a similar osmolality are considered Isotonic.* [[Maltodextrin]] is isotonic at 150g/500ml<ref name="malto"/>.** Therefore Maltodextrin requires ~3.3ml/g of water to be isotonic.* Fructose and glucose ** Fructose and glucose are both 180.16 g/mol.** 300 mmol of Fructose or glucose is therefore 54g (180.16 * 300 / 1000). ** 300 mOsm/kg is 54g/Kg or 26g per 500ml.** Therefore Fructose and Glucose require ~19ml/g of water to be isotonic.* Sucrose (table sugar to refuel )** Sucrose is the musclescombination of one molecule of fructose with one of glucose.** Sucrose is 342.30 g/mol.** However, sucrose is decomposed into glucose and at other times fructose before absorption<ref name="Gray1971"/>, so it will form fathas a similar isotonic concentration as fructose or glucose.** Therefore Sucrose requires ~19ml/g of water to be isotonic.* Salt** Salt is sodium chloride (NaCl), which is 58.44 g/mol (Na:22.99 + Cl:35.45). ** However, during exercise the fast acting carbohydrate will sodium and chloride ions disassociate in water, so 1 mole of NaCl you have 1 mole of Na and 1 mole of Cl, doubling the osmotic pressure.** 300 mmol of salt is 8.7g ((58.44/2) * 300 / 1000)*** 300 mOsm/kg is 8.7g/Kg or 4.4g per 500ml.** 1 gram of sodium implies 2.54g (1/22.99 * 58.44) of salt.** Therefore salt would require ~114 ml/g (500/4.4) of water to be isotonic** If you have just the sodium value, either multiply by 2.54 to get the weight of salt, or use 290 ml/g of sodium.* Potassium** Potassium chloride (KCl), which is 74.55 g/mol (K:39.10 + Cl:35.45).** Like salt, potassium chloride disassociates in water. ** 300 mmol of salt is 11.2g ((74.55/2) * 300 / 1000)*** 300 mOsm/kg is 11.2g/Kg or 5.6g per 500ml.** 1 gram of potassium implies 1.9g (1/39.10 * 74.55) of potassium chloride.** Therefore potassium chloride would require ~89 ml/g (500/5.6) of water to be directly absorbed isotonic** If you have just the potassium value, either multiply by your muscles and not trigger insulin1.9 to get the weight of potassium chloride, or use 169 ml/g of potassium. ==References==
<references>
<ref name="Moseley-2003">{{Cite journal | last1 = Moseley | first1 = L. | last2 = Lancaster | first2 = GI. | last3 = Jeukendrup | first3 = AE. | title = Effects of timing of pre-exercise ingestion of carbohydrate on subsequent metabolism and cycling performance. | journal = Eur J Appl Physiol | volume = 88 | issue = 4-5 | pages = 453-8 | month = Jan | year = 2003 | doi = 10.1007/s00421-002-0728-8 | PMID = 12527977 }}</ref>
<ref name="Jeukendrup-2010">{{Cite journal | last1 = Jeukendrup | first1 = AE. | last2 = Killer | first2 = SC. | title = The myths surrounding pre-exercise carbohydrate feeding. | journal = Ann Nutr Metab | volume = 57 Suppl 2 | issue = | pages = 18-25 | month = | year = 2010 | doi = 10.1159/000322698 | PMID = 21346333 }}</ref>
<ref name="Brun">[http://www.alfediam.org/media/pdf/RevueBrunD&M5-2000.pdf J.F. Brun, C. Fedou, J. Mercier, "Postprandial Reactive Hypoglycemia," ''Diabetes & Metabolism'' (Paris) 2000, 26, 337-351]</ref>
<ref name="Brouns-1989">{{Cite journal | last1 = Brouns | first1 = F. | last2 = Rehrer | first2 = NJ. | last3 = Saris | first3 = WH. | last4 = Beckers | first4 = E. | last5 = Menheere | first5 = P. | last6 = ten Hoor | first6 = F. | title = Effect of carbohydrate intake during warming-up on the regulation of blood glucose during exercise. | journal = Int J Sports Med | volume = 10 Suppl 1 | issue = | pages = S68-75 | month = May | year = 1989 | doi = 10.1055/s-2007-1024956 | PMID = 2663744 }}</ref>
<ref name="Kuipers-1999">{{Cite journal | last1 = Kuipers | first1 = H. | last2 = Fransen | first2 = EJ. | last3 = Keizer | first3 = HA. | title = Pre-exercise ingestion of carbohydrate and transient hypoglycemia during exercise. | journal = Int J Sports Med | volume = 20 | issue = 4 | pages = 227-31 | month = May | year = 1999 | doi = 10.1055/s-2007-971122 | PMID = 10376478 }}</ref>
<ref name="malto">http://www.arniebakercycling.com/pubs/Free/Nutrition%20Maltodextrin%20SS.pdf </ref>
<ref name="Gray1971">{{cite journal|last1=Gray|first1=G M|title=Intestinal Digestion and Maldigestion of Dietary Carbohydrates|journal=Annual Review of Medicine|volume=22|issue=1|year=1971|pages=391–404|issn=0066-4219|doi=10.1146/annurev.me.22.020171.002135}}</ref>
<ref name="Rowlands-2008">{{Cite journal | last1 = Rowlands | first1 = DS. | last2 = Thorburn | first2 = MS. | last3 = Thorp | first3 = RM. | last4 = Broadbent | first4 = S. | last5 = Shi | first5 = X. | title = Effect of graded fructose coingestion with maltodextrin on exogenous 14C-fructose and 13C-glucose oxidation efficiency and high-intensity cycling performance. | journal = J Appl Physiol | volume = 104 | issue = 6 | pages = 1709-19 | month = Jun | year = 2008 | doi = 10.1152/japplphysiol.00878.2007 | PMID = 18369092 }}</ref>
<ref name="isotonic"> http://jap.physiology.org/cgi/content/full/85/5/1941 Hypertonic solutions are less easily absorbed</ref>
<ref name="JacksonTaylor2012">{{cite journal|last1=Jackson|first1=Brian P.|last2=Taylor|first2=Vivien F.|last3=Karagas|first3=Margaret R.|last4=Punshon|first4=Tracy|last5=Cottingham|first5=Kathryn L.|title=Arsenic, Organic Foods, and Brown Rice Syrup|journal=Environmental Health Perspectives|volume=120|issue=5|year=2012|pages=623–626|issn=0091-6765|doi=10.1289/ehp.1104619}}</ref>
<ref name="Sweetness">Sweetness http://biology.clc.uc.edu/courses/bio104/carbohydrates.htm</ref>
</references>