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Carbs during endurance training: why, when and from what source?

Carbs during endurance training: why, when and from what source?

Studies have shown that ingesting carbohydrates during exercise boosts performance. But not all carbohydrates are created equal, and the source and absorption of carbs can make or break your race. What are the best sources of carbohydrates for endurance training and why can high-FODMAP sources such as honey and dates cause stomach issues?

Athletes need carbohydrates, both during exercise and to aid recovery. Many studies have shown that it is beneficial to ingest carbohydrates during medium or high-intensity endurance exercise that lasts over 45 minutes.

Ingesting carbohydrates has also an effect on your recovery. This is especially important if you do multiple events back to back, for example during an intense training period, a stage race or a tournament.

The form and source of carbohydrates make a difference. The right carbohydrate choices help to optimise energy absorption and can help avoid stomach issues.


During exercise, your body runs out of sugar fast

The carbohydrates in our food are called mono-, di-, oligo- and polysaccharides depending on their length. The body uses the long-chain carbohydrates as energy by transforming them into simple sugars in the intestine.

Glucose is the most important energy source for the body, as the majority of the more complex carbohydrates are absorbed as glucose. Some of the glucose is stored in the liver and muscles as glycogen and the rest is transported to the circulation to feed the cells.

During exercise, the amount of glucose used in the muscles multiplies. The fastest way the body can get glucose is from the glycogen stored in the tissues. However, the body’s ability to store glycogen is very limited: the glycogen stores can be depleted entirely during a medium or high-intensity exercise that lasts only 45-90 minutes. That’s why it’s smart to ingest energy that absorbs quickly.

In the chart below, you can see recommended amounts of carbohydrate for exercises of different lengths:

Duration of exercise

Carbs per hour

Less than 1 hour

None or very little

1 to 2 hours


2 to 3 hours


over 3 hours


Ingest glucose and fructose in 2:1 ratio during endurance training

You should not only pay attention to the amount of carbohydrates you ingest during sports but also keep in mind how your body will absorb them. 

Studies have shown that the body can utilise carbohydrates most efficiently during exercise when they are absorbed as glucose and fructose together. Fructose is similar to glucose in its chemical structure, but has a different molecular composition and is absorbed via different transmitter proteins.

When you ingest both glucose and fructose during exercise, you can utilise the body’s ability to absorb sugar optimally by using different transmitter proteins. You can take 60 grams of glucose and 30 grams of fructose in an hour before their respective transmitter proteins are saturated. 

A common recommendation for the ratio of glucose and fructose is 2:1. This ratio enables maximal carbohydrate absorption, as you can ingest up to 90 grams per hour (60g of glucose + 30g of fructose). 

Prevent stomach issues by avoiding FODMAPs during exercise 

As an athlete, it’s smart to find out what kind of carbohydrates your energy source of choice contains and what is the ratio of different sugars. By choosing wisely, you can enhance carbohydrate absorption and prevent stomach issues. 

FODMAPs (Fermentable Oligo-, Di- and Mono-saccharides And Polyols) are short-chain carbohydrates that don’t absorb as well as other carbohydrates in the lower intestine. They can cause gassiness, and for those suffering from irritable bowel syndrome, serious pain and bloating. 

In high quantities, fructose is also counted as a FODMAP. High-FODMAP fructose sources include apples, cherries, honey and dates. As discussed earlier, smaller amounts of fructose absorb well when paired with glucose, but in higher quantities and by itself it doesn’t absorb as well. 

Other FODMAP carbohydrates are lactose, polyols (also known as sugar alcohols), fructans (found in wheat and rye) and inulin (which can be found in several “diet” products as a source of fibre or enhancing the products’ consistency). 


Energy gels and bars made of honey and dates can upset your stomach

Stomach issues can easily put an end to your workout or a race. That’s why it pays off to take a closer look at the list of ingredients in your energy products to see what the source of carbohydrates is. 

May prefer natural sources of energy, such as honey or dates, also during sports. There are a lot of energy products made of honey and dates in the market, but both ingredients are high in FODMAPs, so they can cause pain, gas and bloating to many. 


Nosht products are designed to be easy on your gut

Nosht energy chews and gels are designed to be as easy on the stomach as possible. The ratio of glucose and fructose is 2:1 to ensure efficient energy absorption. The ingredients are all low-FODMAP to further prevent stomach issues.

Carbohydrates in Nosht energy products

It always pays off to look into the list of ingredients. It’s also smart to test your products before a race, so you won’t waste your big day due to stomach upset. During spring, we will tell you more about how to train your gut to be your asset, so remember tune in! 


Fuchs, Gonzales and van Loon: Fructose co-ingestion to increase carbohydrate availability in athletes. J Physiol 597.14 (2019) pp 3549-3560

Betts, Fuchs, Gonzales, and van Loon: Glucose Plus Fructose Ingestion for Post-Exercise Recovery—Greater than the Sum of Its Parts? Nutrients 2017, 9, 344

Jeukendrup A. A step towards personalized sports nutrition: carbohydrate intake during exerciseSports Med 2014; 44(1): 25-33.

Gibson, Peter R. and Shepherd, Susan J. Evidence-based dietary management of functional gastrointestinal symptoms: the FODMAP approach. Journal of gastroenterology and hepatology. Vol 25, issue 2, pg 252-258.

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