Fueling is an essential nutritional strategy used by endurance athletes to fuel their athletic performance during intense exercise.
In combination with carb-loading and muscle recovery, fueling represents the wholesome nutritional strategy every endurance athlete should be familiar with.
In this blog you'll learn all you need to know about fueling.
What is fueling?
Fueling is the intake of carbohydrates during exercise. It is primarily used by cyclists, runners, and triathletes, who because of the intensity of their exercise have elevated energetic needs.
The main purpose of fueling is to slow down glycogen consumption or, in simple terms, give you energy during exercise. Learn more about glycogen and how it affects your athletic performance!
During intense exercise, your body uses the glycogen stored in your muscles and liver to get energy. To prevent glycogen depletion, you need to provide your body with an alternative source of energy.

As you approach your VO2 max, your ability to digest food decreases. For this reason, you need to intake fast acting carbohydrates, such as glucose and fructose, which your body is able to absorb quickly and use instead of glycogen.
Fueling is of vital importance because running out of glycogen is a bad idea. Not only you won't be able to continue with your physical activity, you will also drastically increase stress levels in your body.
Since stress is very detrimental to your health and athletic performance, you should try to avoid stress at all costs. Some athletes use adaptogens such as ashwagandha, while others, if the cause of stress is their expectations, make good use of our tips from a sports psychologist.
Fueling is a nutritional strategy that aims to slow down glycogen consumption by consuming carbohydrates during exercise.
Carbohydrate intake during exercise
The recommended carbohydrate intake for endurance athletes during intense exercise is 60 to 90 grams of carbohydrates per hour.
You should avoid complex carbohydrates, as they will get stuck in your digestive tract. Instead, you should consume simple sugars, such as glucose and fructose.
Glucose is your body's main source of energy (even glycogen is transformed into glucose before being used) with a high glycemic index, which makes it the ideal source of energy during exercise.

The purpose of fructose is to combine it with glucose. A combination of glucose and fructose allows you to use both carbohydrate transporters in your body and increase carbohydrate absorption to 90 grams per hour. For reference, the maximum absorption rate of glucose is 60 grams per hour.
Since proper fueling requires a very high intake of carbohydrates, you need to choose the right tools for the job.
The best strategy for fueling is to absorb 60 to 90 grams of carbohydrates per hour in a combination of glucose and fructose.
Best sources of carbohydrates for fueling
The most efficient way to fuel during intense exercise is by using dietary supplements, such as energy gels and isotonic drinks.
While athletes do try to fuel with regular food, such as bananas, white bread, or even gummy bears, this can often lead to poor performance and digestive issues. It might also be impractical, as chewing while running or cycling doesn't seem to be the best idea ever.
The main advantage of dietary supplements is that:
- they are easy to consume,
- they contain all the necessary nutrients,
- they don't contain unnecessary ingredients.
The things is, during intense exercise, your body only needs three things.
- Carbohydrates
- Water
- Electrolytes
To optimally fuel your body, you need a combination of glucose and fructose (research shows that their optimal ratio is 1:0.8 in favor of glucose).
Since most food is comprised of many nutrients, it is extremely difficult, if not impossible, to hit this target with food. The closest are gummy bears, which are increasingly popular among cyclists, including the renowned nutritionist Dr. Tim Podlogar.
But then there's also this thing about hydration ...
The most efficient way to fuel during intense exercise is by using energy gels or isotonic drinks.
Hydration during intense exercise
During intense exercise, you lose a lot of sweat. This means you lose a lot of body fluid and electrolytes, which you need to replace. This is called hydration.
While fueling and hydration are quite distinct, they usually go hand in hand.
The reason is that when you intake carbohydrates, you also take care of hydration. That is, if you do the right things.
Hydration is extremely important and without proper hydration, even optimal fueling won't be enough.
In order to properly hydrate, you need to intake a sufficient quantity of water and the correct combination of minerals.
Learn more about proper hydration during exercise!
The point of hydration is to provide your body with the fluids and electrolytes lost in sweat during exercise.
Conclusion
Fueling is the nutritional strategy used during exercise by endurance athletes. It is performed by intaking carbohydrates and its goal is to slow down glycogen consumption during exercise.
The best fuel during intense exercise is a combination of two simple sugars, glucose and fructose. Research confirms that the best ratio is 1:0.8 in favor of glucose.
A combination of glucose and fructose allows you to absorb 90 grams of carbohydrates per hour, which seems to be the reasonable upper limit of absorption, although there's plenty of ongoing research in terms of higher intakes.
The most efficient way to fuel is with dietary supplements, such as energy gels and isotonic sports drinks.
Fueling, carb-loading, and recovery comprise the wholesome nutritional strategy of endurance athletes.