The fuels for endurance sports
When exercising, your body will burn both fat and carbohydrate; the more intense the exercise, the greater the demand for carbohydrate will be. Typically, a body has 400-500g (1600-2000kcal) of carbohydrate stored as muscle and liver glycogen. When these carbohydrate reserves are depleted through exercise, your body must rely primarily on fat burning and intense efforts cannot be maintained; this is known as “hitting the wall’ and is common at 2-3 hours if no carbs have been ingested. Your body can adapt and become better at burning fat at low and moderate intensities but will always have to rely on carbohydrate at the high end.
Does carbohydrate really improve performance?
There is extensive research that shows that carbohydrate intake during exercise improves performance. Most of the research shows effects during prolonged exercise (more than 2 hours), but shorter exercise durations can also benefit in some cases. The reasons for the improvements during shorter (around an hour) and longer exercise (more than 2 hours) are completely different. Carbohydrate fueling recommendations are based partly on the duration of the exercise. In general, for longer durations you will need more carbohydrate to optimize performance.
If the exercise is less than 30 min there is no need to take in any carbohydrate. There is little or no evidence that carbohydrate intake or a mouth rinse does anything. It may not harm, but there does not seem to be a need.
Exercise 30-75 min
When the exercise is a little longer, say 30-75 min and it is “all-out” for that duration, performance will benefit from either carbohydrate intake or a carbohydrate mouth rinse. What is best depends on the practicalities of ingesting carbohydrate. Sometimes it is easier to simply rinse and sometimes it will be just as easy to swallow the carbohydrate solution. The type of carbohydrate does not seem to matter much here.
For exercise lasting 1-2 hours, some carbohydrate has been shown to improve performance and 30 grams per hour is probably sufficient. With increasing duration, it is recommended to increase the intake up to 60 g/h and beyond 2.5h even up to 90 g/h. Especially as the exercise duration goes beyond 2h there appears to be a “dose response relationship” and higher intakes are recommended as long as this does not cause stomach problems (or other gastro-intestinal distress).
If the intake is not higher than 60 g/h, any rapidly oxidized carbohydrate will work (glucose, sucrose, maltodextrins and some forms of starch). When the intake is higher than that, it is recommended to use carbohydrate mixes that rely on different transporters; see Carb mixes and benefits for more on this topic.
The recommendation chart
To use the figure above, first establish the duration of your event. That will largely determine the amount of carbohydrate you need. The type of carbohydrate (i.e. multiple-transportable or not) is then dictated by the recommended amount.
The advice in all cases is to practice whatever you are planning to use in a race. Practice - practice - practice. Your gut will adapt and chances of gastro-intestinal discomfort will be reduced; in addition, you will become accustomed to the mechanics of literally “eating on the run”. This practicing is even more crucial at higher carbohydrate intakes. For guidance on nutritional training, please see the CORE Nutrition training guide.
Mix and match
It is important to know that you can mix and match your carbohydrate sources and use drinks, gels, chews and bars depending on your personal preferences. For any solid foods, make sure fat, fiber and protein intake are low so that these ingredients don’t slow down the delivery of carbohydrate and fluids.
Carb sources in products: good news / bad news
The good news about sports nutrition products (gels, chews, sports drinks…) is that they are almost universally formulated with carb sources that are rapidly processed by the body. When fueling at 60g/h or less, product choice is really a matter of preference. The bad news, if you’re looking to fuel at rates over 60g/h, is that many products do not have the appropriate blend of carbohydrate (i.e. they have only / predominantly glucose sources), and it is often not easy to find out which products have the right types / amounts of carbohydrates. Some products contain a small amount of fructose just for taste reasons but this amount is too small to really deliver energy.
CORE will help you to determine how much carbohydrate you need for your event and combines it with hydration advice before turning this into a plan with recommended intake of products you selected.
Jeukendrup, A. E. Nutrition for endurance sports: marathon, triathlon, and road cycling." J Sports Sci 29 Suppl 1: S91-99, 2011.
Jeukendrup, A. (2014). A step towards personalized sports nutrition: carbohydrate intake during exercise." Sports Med 44 Suppl 1: 25-33, 2014.