Carbohydrates are an important source of energy for our body. Even if we do not consume carbohydrates, the body produces carbohydrates itself from other substances such as amino acids or lactate in order to maintain a constant blood sugar level. The intake of carbohydrates is essential when exercising at high intensity. However, there is a wide variety of different carbohydrates, some of which have different effects on energy supply. Carbohydrates occur in different forms. They can join together to form large molecular chains or appear in their simplest form as monosaccharides.
Not all carbohydrates are the same
The different types of carbohydrates in our diet make a difference to our health. Carbohydrates vary in length, and this length refers to the number of molecules and atoms of each carbohydrate. In order to digest carbohydrates, they have to be cut or broken down by our gastrointestinal tract. Long-chain carbohydrates, such as starch, are broken down into short-chain carbohydrates. This takes some time, which is why long-chain carbohydrates provide energy less quickly than short-chain carbohydrates. Short-chain carbohydrates are sugar. However, not all sugars are the same. There are also differences between sugars. Sugars occur as monosaccharides and disaccharides. The best-known representatives of simple sugars are fructose and glucose. Fruit sugar is also known as fructose. Dextrose is also called dextrose or glucose, although glucose is the most common name. Our common household sugar is a disaccharide and is also called cane sugar, beet sugar or sucrose. As the name “disaccharide” suggests, it consists of two monosaccharides. One part is fructose and the second part is glucose. Diabetics are particularly familiar with the latter term, glucose, in connection with their blood sugar measurement. The type of sugar in our blood is glucose, the blood sugar. If we eat fructose, our blood sugar does not increase immediately, as fructose must first be converted into glucose in order to increase blood sugar. The term glucose could suggest that this sugar is found particularly in grapes. In fact, fruit always contains a proportion of dextrose (glucose), but also a proportion of fructose and a small proportion of the disaccharide sucrose. In most types of fruit, glucose and fructose are roughly half and half. In grapes, the proportion of fructose is even slightly higher than the proportion of glucose, depending on the variety. Glucose was first isolated as a molecule in grapes in the 18th century and was thus given the name grape sugar. Fructose tastes sweeter than glucose, which means that less of it is needed for the same sweet taste when used in sweets, which saves money in production. In addition, fructose is now the cheapest sugar for the industry to produce. The individual types of sugar therefore have an influence on the sweet taste and sweetening power of sports drinks. Based on the respective composition, an athlete can estimate this and choose the right sweetness for themselves. The sweetening power or sweet taste is an important factor in sports drinks, especially during prolonged exercise. Another simple sugar is galactose, which together with glucose forms the disaccharide lactose. Both galactose and lactose hardly play a role in sports nutrition as a source of energy. Some of the dietary fibres contained in food are also carbohydrates, but cannot be broken down by our body’s enzymes to produce energy, so they are excreted undigested. However, some of the dietary fibers can be converted into alternative energy sources such as fatty acids by bacteria in our intestinal flora and are later available to us as energy.
Maltodextrin in sports drinks
Long-chain carbohydrates are used less frequently in sport. Complex carbohydrates in particular, which are additionally bound to dietary fiber, are not found during high exertion, such as in competition (exceptions include ultra-distance competitions, which are not covered here). The longer digestion process can lead to additional strain on the gastrointestinal tract, which is particularly undesirable in competition. As digestion takes longer, energy arrives in the body with a delay, which can lead to “energy gaps” with a loss of performance and also makes it more difficult to control nutrition during competitions. Maltodextrin represents a compromise here. Maltodextrin consists of a longer chain of the simple sugar glucose. A distinction is made between the shorter chain of maltodextrin 19, the medium chain length of maltodextrin 12 and the longest carbohydrate chain of maltodextrin 6. In general, the body can break down maltodextrin into the individual sugars quickly and easily. The breakdown is fast and the energy supply, especially with maltodextrin 19, is almost as fast as with pure glucose. If dosed correctly, maltodextrin rarely causes digestive problems. Many manufacturers of sports drinks and energy powders use maltodextrin, although the chain length is usually not explicitly stated and it is often a mixture of different types of maltodextrin. Maltodextrin dissolves well in water. This maltodextrin solution is less viscous than a pure glucose solution and therefore has a lower viscosity, which makes it easier to drink and swallow. A major advantage of maltodextrin is that the concentration of dissolved particles in water (osmolarity) is low, which means that the maltodextrin solution quickly provides hydration and energy. Maltodextrin is often combined with fructose in gels and sports drinks, which, in addition to the energy aspect, also has to do with the fact that maltodextrin has hardly any sweetness, whereas the sweetening power of fructose is correspondingly higher (see above).
Which and how many carbohydrates in sports drinks
The following applies to the majority of carbohydrates eaten and drunk: if carbohydrates or simple sugars are used to generate energy, this is done via glycolysis, the breakdown of simple sugars. Ultimately, it is the two simple sugars glucose and fructose that provide our body with energy during sport.
Three factors are decisive in sports nutrition:
- the absolute dosage of carbohydrates
- the ratio of the two sugars glucose and fructose in sports drinks (bars etc.)
- the (chemical) form of sugar intake
The simple sugars glucose and fructose can initially have a different chemical form than the pure form of the simple sugars when ingested orally. As described above, the simple sugar glucose often occurs as maltodextrin in the form of a longer molecular chain. Glucose and fructose can also be found in sports drinks as disaccharides, although this is usually the form of the disaccharide sucrose. Other disaccharides such as isomaltulose, which also consists of glucose and fructose, are becoming increasingly common. Isomaltulose has the advantage over classic sucrose that it is broken down and absorbed more slowly. As a result, the blood sugar level rises much more slowly. As the bacteria in the oral flora can hardly utilize isomaltulose, potential damage to the teeth is reduced, which can be a negative side effect of normal household sugar, especially when consumed in high-sugar drinks. However, isomaltulose can lead to digestive problems if consumed in large quantities and can have a laxative effect if consumed in excess.
For easy training rides, an intake of 40 grams of carbohydrates per hour (g/h) is sufficient. While a maximum intake of 60 g/h used to be specified for higher levels of exertion, it is now advisable to consume twice as much under enormous exertion. However, the amount of carbohydrate must be linked to the intake of sugars. This has to do with the absorption of simple sugars in the small intestine. If the concentration of the respective sugars exceeds the absorption capacity, this can lead to severe digestive problems. A fructose:glucose ratio of 0.5 (1:2) is often recommended. In many studies, this ratio has made it possible to consume higher doses of carbohydrates without digestive problems, while at the same time improving performance. Furthermore, the intake of larger quantities of 90 to 100 g/h is recommended, especially for an exercise duration of more than 2 to 3 hours. The aim is not only to provide sufficient energy for the exertion, but also to conserve the carbohydrate stores (glycogen) in the muscles and liver.
However, not every athlete can tolerate large amounts of carbohydrates and/or fructose. An overdose of carbohydrates can impair performance in competition. The intake of fructose in particular is highly individual. Some people tolerate virtually no fructose. In this case, the maximum intake of glucose of around 60 grams per hour is the measure of all things. Otherwise, it is important to find your personal optimum. To avoid or mitigate the problem of fructose intolerance, the tolerance of fructose and carbohydrate mixtures can be trained through regular consumption (train the gut).
For a few years now, the standard mixing ratio (fructose:glucose ratio 1:2) has been increasingly abandoned. There are now several studies on a fructose:glucose ratio of 0.8 (4:5), which show an associated increase in performance and relatively low digestive complaints, even with higher absolute carbohydrate levels. The absolute carbohydrate oxidation rate as well as the oxidation efficiency were highest with this mixing ratio compared to other mixing ratios. Interestingly, the oxidation rate and efficiency of glucose was also the highest, even though a (2:1) mixture contains more absolute glucose. The oxidation efficiency of fructose was also highest at (4:5) and there was a moderate increase in endurance performance. Thus, the fructose: glucose ratio of 0.8 (4:5) compared to the 0.5 (1:2) ratio appears to be beneficial for athletic performance, as it prevents the decrease in liver glycogen content, but without affecting muscle glycogen breakdown. However, this ratio requires a good tolerance of fructose. This should be extensively tested and confirmed before competitions.
Conclusion:
Carbohydrates should be consumed in as high a concentration as possible during heavy exercise. Quickly digestible carbohydrates or sugars are the first choice here. The tolerance of high doses and different types of sugar must be tested and practiced individually. In studies, a 2:1 ratio of glucose to fructose with 90 grams of carbohydrates per hour shows the best results for most athletes in terms of tolerance and performance.
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Literature:
Leiper JB, Intestinal water absorption–implications for the formulation of rehydration solutions. Int J Sports Med. 1998 Jun;19 Suppl 2:S129-32. doi: 10.1055/s-2007-971977. PMID: 9694418.
Evans GH, Watson P, Shirreffs SM, Maughan RJ. Effect of Exercise Intensity on Subsequent Gastric Emptying Rate in Humans. Int J Sport Nutr Exerc Metab. 2016 Apr;26(2):128-34. doi: 10.1123/ijsnem.2015-0110. Epub 2015 Aug 31. PMID: 26322651.
Pouderoux P, Friedman N, Shirazi P, Ringelstein JG, Keshavarzian A. Effect of carbonated water on gastric emptying and intragastric meal distribution. Dig Dis Sci. 1997 Jan;42(1):34-9. doi: 10.1023/a:1018820718313. PMID: 9009113.
Lau ERL, Henry CJ. No influence of carbonation on glycemic response, gastric emptying, and satiety of sweetened drinks. Nutrition. 2017 Jul-Aug;39-40:1-7. doi: 10.1016/j.nut.2017.02.001. Epub 2017 Mar 1. PMID: 28606564.
O’Brien WJ, Stannard SR, Clarke JA, Rowlands DS. Fructose-maltodextrin ratio governs exogenous and other CHO oxidation and performance. Med Sci Sports Exerc. 2013 Sep;45(9):1814-24. doi: 10.1249/MSS.0b013e31828e12d4. PMID: 23949097.
Bally L, Kempf P, Zueger T, Speck C, Pasi N, Ciller C, Feller K, Loher H, Rosset R, Wilhelm M, Boesch C, Buehler T, Dokumaci AS, Tappy L, Stettler C. Metabolic Effects of Glucose-Fructose Co-Ingestion Compared to Glucose Alone during Exercise in Type 1 Diabetes. Nutrients. 2017 Feb 21;9(2):164. doi: 10.3390/nu9020164. PMID: 28230765; PMCID: PMC5331595.
Rosset R, Egli L, Lecoultre V. Glucose-fructose ingestion and exercise performance: The gastrointestinal tract and beyond. Eur J Sport Sci. 2017 Aug;17(7):874-884. doi: 10.1080/17461391.2017.1317035. Epub 2017 Apr 25. PMID: 28441908.
Jeukendrup AE. Training the Gut for Athletes. Sports Med. 2017 Mar;47(Suppl 1):101-110. doi: 10.1007/s40279-017-0690-6. PMID: 28332114; PMCID: PMC5371619.
Rowlands DS, Thorburn MS, Thorp RM, Broadbent S, Shi X. Effect of graded fructose coingestion with maltodextrin on exogenous 14C-fructose and 13C-glucose oxidation efficiency and high-intensity cycling performance. J Appl Physiol (1985). 2008 Jun;104(6):1709-19. doi: 10.1152/japplphysiol.00878.2007. Epub 2008 Mar 27. PMID: 18369092.
Jang C, Hui S, Lu W, Cowan AJ, Morscher RJ, Lee G, Liu W, Tesz GJ, Birnbaum MJ, Rabinowitz JD. The Small Intestine Converts Dietary Fructose into Glucose and Organic Acids. Cell Metab. 2018 Feb 6;27(2):351-361.e3. doi: 10.1016/j.cmet.2017.12.016. PMID: 29414685; PMCID: PMC6032988.
Jeukendrup AE. Carbohydrate and exercise performance: the role of multiple transportable carbohydrates. Curr Opin Clin Nutr Metab Care. 2010 Jul;13(4):452-7. doi: 10.1097/MCO.0b013e328339de9f. PMID: 20574242.
Hearris MA, Pugh JN, Langan-Evans C, Mann SJ, Burke L, Stellingwerff T, Gonzalez JT, Morton JP. 13C-glucose-fructose labeling reveals comparable exogenous CHO oxidation during exercise when consuming 120 g/h in fluid, gel, jelly chew, or coingestion. J Appl Physiol (1985). 2022 Jun 1;132(6):1394-1406. doi: 10.1152/japplphysiol.00091.2022. Epub 2022 Apr 21. PMID: 35446596.
Holloszy JO. Exercise-induced increase in muscle insulin sensitivity. J Appl Physiol (1985). 2005 Jul;99(1):338-43. doi: 10.1152/japplphysiol.00123.2005. PMID: 16036907.
Hundal HS, Darakhshan F, Kristiansen S, Blakemore SJ, Richter EA. GLUT5 expression and fructose transport in human skeletal muscle. Adv Exp Med Biol. 1998;441:35-45. doi: 10.1007/978-1-4899-1928-1_4. PMID: 9781312.
Zierath JR, Nolte LA, Wahlström E, Galuska D, Shepherd PR, Kahn BB, Wallberg-Henriksson H. Carrier-mediated fructose uptake significantly contributes to carbohydrate metabolism in human skeletal muscle. Biochem J. 1995 Oct 15;311 ( Pt 2)(Pt 2):517-21. doi: 10.1042/bj3110517. PMID: 7487889; PMCID: PMC1136029.
Dholariya SJ, Orrick JA. Biochemistry, Fructose Metabolism. 2022 Oct 17. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan–. PMID: 35015453.
Maughan RJ, Noakes TD. Fluid replacement and exercise stress. A brief review of studies on fluid replacement and some guidelines for the athlete. Sports Med. 1991 Jul;12(1):16-31. doi: 10.2165/00007256-199112010-00003. PMID: 1925187.
Jeukendrup AE, Wagenmakers AJ, Stegen JH, Gijsen AP, Brouns F, Saris WH. Carbohydrate ingestion can completely suppress endogenous glucose production during exercise. Am J Physiol Endocrinol Metab 276: E672–E683, 1999.
Rowlands DS, Kopetschny BH, Badenhorst CE. The Hydrating Effects of Hypertonic, Isotonic and Hypotonic Sports Drinks and Waters on Central Hydration During Continuous Exercise: A Systematic Meta-Analysis and Perspective. Sports Med. 2022 Feb;52(2):349-375. doi: 10.1007/s40279-021-01558-y. Epub 2021 Oct 30. PMID: 34716905; PMCID: PMC8803723.
King AJ, O’Hara JP, Arjomandkhah NC, Rowe J, Morrison DJ, Preston T, King RFGJ. Liver and muscle glycogen oxidation and performance with dose variation of glucose-fructose ingestion during prolonged (3 h) exercise. Eur J Appl Physiol. 2019 May;119(5):1157-1169. doi: 10.1007/s00421-019-04106-9. Epub 2019 Mar 6. PMID: 30840136; PMCID: PMC6469629.
O’Brien WJ, Rowlands DS. Fructose-maltodextrin ratio in a carbohydrate-electrolyte solution differentially affects exogenous carbohydrate oxidation rate, gut comfort, and performance. Am J Physiol Gastrointest Liver Physiol. 2011 Jan;300(1):G181-9. doi: 10.1152/ajpgi.00419.2010. Epub 2010 Nov 11. PMID: 21071509.
