Fructose as an energy source for exercise
Fructose as an energy source for exercise
During exercise the rapid demand for energy means that carbohydrates with a high glycaemic index (GI) are preferred. These get into the bloodstream much faster and help you to keep up with the demands of your activity.
Fructose is the sugar in fruit. It is sometimes included in sports nutrition products because it is absorbed via a different pathway to glucose, potentially increasing your maximum carbohydrate intake from 60g per hour to 90g per hour.
The issue is that fructose is a low GI sugar, meaning it takes much longer to get into the bloodstream. Even then, once fructose is in the bloodstream it has to be processed by the liver before it can be turned into a fuel source that your muscles can use. This process can take up to 90 minutes.
You also need to be aware that fructose is a simple sugar, which can create an increased risk of gastric distress if you don’t take enough water on board with it to dilute the concentration
Simple sugars also feed the bacteria in the gut, which can result in more gas being produced – and, in turn, this can cause bloating and cramps.
This all means that fructose can be useful as an energy source if you are doing an activity for longer than three or four hours and have taken in your full hourly quota of 60g of carbohydrate from other sources, such as maltodextrin, glucose or dextrose. However, it’s advisable to practise using fructose in training and be confident that it doesn’t cause you any additional gut issues before relying on it in a race or long sportive.
Maltodextrin is a better energy choice for a sports drink. It still has a high glycaemic index, meaning that the energy is available quickly, but does not carry the same gastric distress risk that simple sugars do.