This blog explores which carbohydrates are used more quickly than others. The ideal carbohydrate during exercise is rapidly emptied from the stomach, does not need digestion or is digested very rapidly, is absorbed quickly and can immediately be used by the muscle.
Since the 1980s it has been known that carbohydrate intake during exercise can improve exercise performance lasting two hours or longer. Soon after this discovery, it was established that not all carbohydrates are equal and carbohydrates ingested during exercise may be utilised at different rates. Recently it was also demonstrated that there is a dose response relationship between the amount of carbohydrate ingested and oxidized and performance during prolonged exercise. Therefore it is important to identify carbohydrate sources that are oxidised rapidly.
The ideal carbohydrate during exercise is rapidly emptied from the stomach, does not need digestion or is digested very rapidly, is absorbed quickly and can immediately be used by the muscle. This blog is based on a large number of studies and references and the reader interested in more detail is referred to the review articles listed at the bottom of this blog, that are downloadable in their entirety free of charge.
Carbohydrate use from a drink is limited to 60 g/h
Carbohydrates ingested during exercise can be oxidised at a rate no higher than 1g/min (60g/h), independent of the type of carbohydrate. So even when you would ingest large amounts of glucose for example, say 100 g/h, no more than 60 g/h would be utilised. This is reflected in guidelines published by the American College of Sports Medicine (ACSM) from 2007–2009 which recommended that, during exercise lasting more than one hour, athletes should consume carbohydrate at hourly rates of between 30 and 60g. In one study, carbohydrate was ingested at rates up to 3g/min (180g/h) (A “don’t try this at home” intake), the oxidation of the ingested carbohydrate did not exceed 1g/min (60g/h).
Carbohydrates ingested during exercise can be oxidised at a rate no higher than 1g/min (60g/h)
Differences between carbohydrates
Some carbohydrate are faster than others but no carbohydrates can be oxidized at rates of approximately 60 g/h. The faster carbohydrates include glucose (grape sugar), sucrose (table sugar), maltose (milk sugar), maltodextrins and some starches. Also some starches can be oxidized at very high rates. Some carbohydrates that are slower include fructose (fruitsugar), galactose, trehalose and some starches (those that are not very well soluble in water).
Apparently the digestion of maltodextrins (a chain of 10-20 glucose molecules) is not limiting and neither is the breakdown of the very large chain of glucose molecules in some starches. Fructose and galactose, however, are absorbed slower and need to be converted in the liver first before they can be used by the muscle. Fructose, for example, is converted to glucose or lactate, both of which are very good sources of energy for the muscle, but the conversions slows down the process.
Some carbohydrate are faster than others but no single carbohydrate can be oxidized at rates higher than approximately 60 g/h
If fructose is ingested at high rates (and it is not ingested with another carbohydrate), it is known to result in gastro-intestinal discomfort. The same has been observed for galactose. During exercise, it is recommended to choose a carbohydrate that is rapidly oxidized, so it does not accumulate in the intestine.
Most carbohydrate drinks on the market aimed at the endurance