The Science of Energy Gels
Contents
1 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.
1.1 Required Dilution – Isotonic Drinks
Isotonic drinks have a similar concentration (osmolality) of carbohydrate and electrolytes to the human blood and are easier to absorb[1]. 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.
1.2 Absorption Rate - Glycemic Index
Main article: 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 actually has a glycemic index of over 100, with values between 105 and 136.
- Fructose has a low glycemic index of 19, as it has to go via the liver to be converted to glucose.
1.3 Digestive Path
While fructose has a low isotonic concentration and a low glycemic index, it can be absorbed via a different path (GLUT5) to glucose and Maltodextrin (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[2].
2 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)[3].
- 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[3].
- 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% maltose (2 glucose molecules) and 52% 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[4].
- 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.
3 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[5]. This condition effects some athletes who take carbohydrate before exercise[6], but not if the carbohydrate is taken during the warm up[7] or immediately before exercise[8]. It appears this hypoglycemia is specific to some individuals[9]. However, there appears to be no performance impact from this hypoglycemia[8] and I found no reports of hypoglycemia in response to carbohydrate taken during exercise.
4 Isotonic Calculations
For those interested, there is the math behind the isotonic calculations I use on my 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[10].
- 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[11], 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.
5 References
- ↑ http://jap.physiology.org/cgi/content/full/85/5/1941 Hypertonic solutions are less easily absorbed
- ↑ Rowlands, DS.; Thorburn, MS.; Thorp, RM.; Broadbent, S.; Shi, X. (Jun 2008). "Effect of graded fructose coingestion with maltodextrin on exogenous 14C-fructose and 13C-glucose oxidation efficiency and high-intensity cycling performance.". J Appl Physiol 104 (6): 1709-19. Template:citation/identifier. Template:citation/identifier.
- ↑ 3.0 3.1 Sweetness http://biology.clc.uc.edu/courses/bio104/carbohydrates.htm
- ↑ Template:cite journal
- ↑ J.F. Brun, C. Fedou, J. Mercier, "Postprandial Reactive Hypoglycemia," Diabetes & Metabolism (Paris) 2000, 26, 337-351
- ↑ Kuipers, H.; Fransen, EJ.; Keizer, HA. (May 1999). "Pre-exercise ingestion of carbohydrate and transient hypoglycemia during exercise.". Int J Sports Med 20 (4): 227-31. Template:citation/identifier. Template:citation/identifier.
- ↑ Brouns, F.; Rehrer, NJ.; Saris, WH.; Beckers, E.; Menheere, P.; ten Hoor, F. (May 1989). "Effect of carbohydrate intake during warming-up on the regulation of blood glucose during exercise.". Int J Sports Med 10 Suppl 1: S68-75. Template:citation/identifier. Template:citation/identifier.
- ↑ 8.0 8.1 Jeukendrup, AE.; Killer, SC. (2010). "The myths surrounding pre-exercise carbohydrate feeding.". Ann Nutr Metab 57 Suppl 2: 18-25. Template:citation/identifier. Template:citation/identifier.
- ↑ Moseley, L.; Lancaster, GI.; Jeukendrup, AE. (Jan 2003). "Effects of timing of pre-exercise ingestion of carbohydrate on subsequent metabolism and cycling performance.". Eur J Appl Physiol 88 (4-5): 453-8. Template:citation/identifier. Template:citation/identifier.
- ↑ http://www.arniebakercycling.com/pubs/Free/Nutrition%20Maltodextrin%20SS.pdf
- ↑ Template:cite journal
