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From Fellrnr.com, Running tips
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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
=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]].
** 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>
