View source for The Science of Energy Gels

[[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 =
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 the digestive path in the gut.
==Required Dilution – Isotonic Drinks==
Isotonic drinks have a similar concentration (osmolality) of carbohydrate and electrolytes to the human blood and are easier to absorb<ref name="isotonic"/>.  The concentration is based on the number of molecules rather than the weight, so an isotonic drink with bigger molecules has more carbohydrate by weight. [[Maltodextrin]] is a long molecule that is a chain of glucose, so you can have a lot of it in an isotonic solution. Maltodextrin is isotonic at 150g/500ml, where fructose, glucose and sucrose (table sugar) are isotonic at 26g/500ml. This means that you need to dilute the simple sugars with six times as much water as Maltodextrin. 
==Absorption Rate - Glycemic Index==
{{Main|Glycemic Index}}
Glycemic index reflects how high a carbohydrate raises the blood sugar level. 
* Glucose is the standard against which everything else is measured, so it has a Glycemic Index of 100. Glucose is used because it raises the blood sugar faster than almost anything else. 
* [[Maltodextrin| Maltodextrin]] actually has a glycemic index of over 100, with values between 105 and 136. 
* [[Fructose| Fructose]] has a low glycemic index of 19, as it has to go via the liver to be converted to glucose. 
==Digestive 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 ([http://en.wikipedia.org/wiki/GLUT2 GLUT2]). This means that if you have enough glucose or Maltodextrin to saturate that absorption path, adding fructose will improve the overall usage of the carbohydrate intake<ref name="Rowlands-2008"/>. 
==Optimal Carbohydrate Intake==
Most studies have shown that glucose and Maltodextrin can be absorbed and metabolized at up to 1.0 grams/minute, while Fructose is absorbed and metabolized at up to 0.6 grams/minute<ref name="Jeukendrup2004"/>. Combining Fructose with glucose/Maltodextrin can result in the metabolism of up to 1.75 grams/minute<ref name="Jeukendrup2010"/>. 
=Ingredient Analysis=
Here is an analysis of the most common ingredients 
* '''Maltodextrin''' is the best form of carbohydrate, and 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="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 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"/>. 
* '''Fat''' can make a gel more palatable and is a useful fuel source at ultramarathon 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, but the evidence is unclear at the levels provided in most gels. 
* '''[[Caffeine]] '''is great for improving performance and speeding the absorption of carbohydrate. 
* '''beta-Alanine''' is an amino acid contained in Chia Surge. Most studies have shown that beta-Alanine will improve sprint performance<ref name="Hoffman-2008"/><ref name="Artioli-2010"/><ref name="Baguet-2010"/><ref name="Van Thienen-2009"/><ref name="Derave-2007"/>, with only one showing no benefit<ref name="Sweeney-2010"/>. Note that most studies used 2-6g/day of beta-Alanine, which is 4-12 packets of Chia Surge per day. Beta-Alanine may cause a harmless tingling of the skin<ref name="Artioli-2010"/>.
=Reactive Hypoglycemia =
In some people their blood sugar will 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 I found no reports of hypoglycemia in response to carbohydrate taken during exercise. 
=Viscosity=
[[File:Gel Viscosity.JPG|right|thumb|200px|The funnel and measure used to test the viscosity of gels.]]
For the [[Comparison of Energy Gels]] the viscosity of gels was simplistically measured by measuring the time it takes for 5ml to flow through a funnel. The temperature for all tests was approximately 68f/20c. 
=Isotonic Calculations=
For those interested, there is the 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)
** Sucrose is the combination of one molecule of fructose with one of glucose.
** Sucrose is 342.30 g/mol.
** However, sucrose is decomposed into glucose and fructose before absorption<ref name="Gray1971"/>, so it has 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, the 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 isotonic
** If you have just the potassium value, either multiply by 1.9 to get the weight of potassium chloride, or use 169 ml/g of potassium.
=References=
<references>
<ref name="Moseley-2003">L. Moseley, GI. Lancaster, AE. Jeukendrup, Effects of timing of pre-exercise ingestion of carbohydrate on subsequent metabolism and cycling performance., Eur J Appl Physiol, volume 88, issue 4-5, pages 453-8, Jan 2003, doi [http://dx.doi.org/10.1007/s00421-002-0728-8 10.1007/s00421-002-0728-8], PMID [http://www.ncbi.nlm.nih.gov/pubmed/12527977 12527977]</ref>
<ref name="Jeukendrup-2010">AE. Jeukendrup, SC. Killer, The myths surrounding pre-exercise carbohydrate feeding., Ann Nutr Metab, volume 57 Suppl 2, pages 18-25,  2010, doi [http://dx.doi.org/10.1159/000322698 10.1159/000322698], PMID [http://www.ncbi.nlm.nih.gov/pubmed/21346333 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">F. Brouns, NJ. Rehrer, WH. Saris, E. Beckers, P. Menheere, F. ten Hoor, Effect of carbohydrate intake during warming-up on the regulation of blood glucose during exercise., Int J Sports Med, volume 10 Suppl 1, pages S68-75, May 1989, doi [http://dx.doi.org/10.1055/s-2007-1024956 10.1055/s-2007-1024956], PMID [http://www.ncbi.nlm.nih.gov/pubmed/2663744 2663744]</ref>
<ref name="Kuipers-1999">H. Kuipers, EJ. Fransen, HA. Keizer, Pre-exercise ingestion of carbohydrate and transient hypoglycemia during exercise., Int J Sports Med, volume 20, issue 4, pages 227-31, May 1999, doi [http://dx.doi.org/10.1055/s-2007-971122 10.1055/s-2007-971122], PMID [http://www.ncbi.nlm.nih.gov/pubmed/10376478 10376478]</ref>
<ref name="malto">http://www.arniebakercycling.com/pubs/Free/Nutrition%20Maltodextrin%20SS.pdf </ref>
<ref name="Gray1971">G M Gray, Intestinal Digestion and Maldigestion of Dietary Carbohydrates, Annual Review of Medicine, volume 22, issue 1, 1971, pages 391–404, ISSN [http://www.worldcat.org/issn/0066-4219 0066-4219], doi [http://dx.doi.org/10.1146/annurev.me.22.020171.002135 10.1146/annurev.me.22.020171.002135]</ref>
<ref name="Rowlands-2008">DS. Rowlands, MS. Thorburn, RM. Thorp, S. Broadbent, X. Shi, Effect of graded fructose coingestion with maltodextrin on exogenous 14C-fructose and 13C-glucose oxidation efficiency and high-intensity cycling performance., J Appl Physiol, volume 104, issue 6, pages 1709-19, Jun 2008, doi [http://dx.doi.org/10.1152/japplphysiol.00878.2007 10.1152/japplphysiol.00878.2007], PMID [http://www.ncbi.nlm.nih.gov/pubmed/18369092 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">Brian P. Jackson, Vivien F. Taylor, Margaret R. Karagas, Tracy Punshon, Kathryn L. Cottingham, Arsenic, Organic Foods, and Brown Rice Syrup, Environmental Health Perspectives, volume 120, issue 5, 2012, pages 623–626, ISSN [http://www.worldcat.org/issn/0091-6765 0091-6765], doi [http://dx.doi.org/10.1289/ehp.1104619 10.1289/ehp.1104619]</ref>
<ref name="Sweetness">Sweetness http://biology.clc.uc.edu/courses/bio104/carbohydrates.htm</ref>
<ref name="Jeukendrup2004">Asker E Jeukendrup, Carbohydrate intake during exercise and performance, Nutrition, volume 20, issue 7-8, 2004, pages 669–677, ISSN [http://www.worldcat.org/issn/08999007 08999007], doi [http://dx.doi.org/10.1016/j.nut.2004.04.017 10.1016/j.nut.2004.04.017]</ref>
<ref name="Jeukendrup2010">Asker E Jeukendrup, Carbohydrate and exercise performance: the role of multiple transportable carbohydrates, Current Opinion in Clinical Nutrition and Metabolic Care, volume 13, issue 4, 2010, pages 452–457, ISSN [http://www.worldcat.org/issn/1363-1950 1363-1950], doi [http://dx.doi.org/10.1097/MCO.0b013e328339de9f 10.1097/MCO.0b013e328339de9f]</ref>
<ref name="Van Thienen-2009"> R. Van Thienen, K. Van Proeyen, B. Vanden Eynde, J. Puype, T. Lefere, P. Hespel, Beta-alanine improves sprint performance in endurance cycling., Med Sci Sports Exerc, volume 41, issue 4, pages 898-903, Apr 2009, doi [http://dx.doi.org/10.1249/MSS.0b013e31818db708 10.1249/MSS.0b013e31818db708], PMID [http://www.ncbi.nlm.nih.gov/pubmed/19276843 19276843]</ref>
<ref name="Hoffman-2008"> JR. Hoffman, NA. Ratamess, AD. Faigenbaum, R. Ross, J. Kang, JR. Stout, JA. Wise, Short-duration beta-alanine supplementation increases training volume and reduces subjective feelings of fatigue in college football players., Nutr Res, volume 28, issue 1, pages 31-5, Jan 2008, doi [http://dx.doi.org/10.1016/j.nutres.2007.11.004 10.1016/j.nutres.2007.11.004], PMID [http://www.ncbi.nlm.nih.gov/pubmed/19083385 19083385]</ref>
<ref name="Artioli-2010"> GG. Artioli, B. Gualano, A. Smith, J. Stout, AH. Lancha, Role of beta-alanine supplementation on muscle carnosine and exercise performance., Med Sci Sports Exerc, volume 42, issue 6, pages 1162-73, Jun 2010, doi [http://dx.doi.org/10.1249/MSS.0b013e3181c74e38 10.1249/MSS.0b013e3181c74e38], PMID [http://www.ncbi.nlm.nih.gov/pubmed/20479615 20479615]</ref>
<ref name="Baguet-2010"> A. Baguet, K. Koppo, A. Pottier, W. Derave, Beta-alanine supplementation reduces acidosis but not oxygen uptake response during high-intensity cycling exercise., Eur J Appl Physiol, volume 108, issue 3, pages 495-503, Feb 2010, doi [http://dx.doi.org/10.1007/s00421-009-1225-0 10.1007/s00421-009-1225-0], PMID [http://www.ncbi.nlm.nih.gov/pubmed/19841932 19841932]</ref>
<ref name="Sweeney-2010"> KM. Sweeney, GA. Wright, A. Glenn Brice, ST. Doberstein, The effect of beta-alanine supplementation on power performance during repeated sprint activity., J Strength Cond Res, volume 24, issue 1, pages 79-87, Jan 2010, doi [http://dx.doi.org/10.1519/JSC.0b013e3181c63bd5 10.1519/JSC.0b013e3181c63bd5], PMID [http://www.ncbi.nlm.nih.gov/pubmed/19935102 19935102]</ref>
<ref name="Derave-2007"> W. Derave, MS. Ozdemir, RC. Harris, A. Pottier, H. Reyngoudt, K. Koppo, JA. Wise, E. Achten, beta-Alanine supplementation augments muscle carnosine content and attenuates fatigue during repeated isokinetic contraction bouts in trained sprinters., J Appl Physiol, volume 103, issue 5, pages 1736-43, Nov 2007, doi [http://dx.doi.org/10.1152/japplphysiol.00397.2007 10.1152/japplphysiol.00397.2007], PMID [http://www.ncbi.nlm.nih.gov/pubmed/17690198 17690198]</ref>
</references>