Exogenous carbohydrate oxidation

Exogenous carbohydrate oxidation refers to the process of burning carbohydrates that have been consumed during exercise rather than drawing on the body’s glycogen stores. It measures how much of the ingested carbohydrate is converted to energy by working muscles.

Explanation

During endurance activities, athletes often consume drinks or gels to maintain blood glucose and delay fatigue. These carbohydrates must be digested, absorbed and transported to muscles before they can be oxidised. Glucose ingested during exercise is transported into the bloodstream by SGLT1; when intake rates exceed about 60 g per hour, the transporter becomes saturated and oxidation plateaus at roughly 0.9–1.1 g per minute. Adding fructose or another sugar that uses a different transporter can raise total absorption and oxidation rates. Studies report that combining glucose and fructose can elevate exogenous carbohydrate oxidation to approximately 1.5–1.75 g per minute—around 65 % higher than glucose alone. This additional fuel helps spare muscle glycogen and sustain high-intensity exercise. However, there is still an upper limit; consuming more than about 90 g of carbohydrate per hour offers little extra benefit and may cause gastrointestinal distress. Training the gut and gradually increasing carbohydrate intake improves tolerance and uptake.

Practical considerations for exogenous carb use

An athlete drinking 500 mL of a 6 % glucose beverage per hour (providing 30 g/h) will typically oxidise about 0.5 g of exogenous carbohydrate per minute. Increasing intake to 60 g/h with glucose alone can raise oxidation close to 1 g/min, while a mix of 60 g/h glucose and 30 g/h fructose may approach 1.5 g/min. This higher rate provides more energy but requires careful planning to avoid stomach upset. Breaking total intake into frequent sips, pairing different sugars and practising during training sessions are key strategies. For shorter events under an hour, exogenous carbohydrate oxidation is less important because glycogen stores suffice. For races lasting over two hours, a high, balanced intake can significantly improve performance.

Understanding exogenous carbohydrate oxidation helps athletes plan their fueling strategies to deliver the right amount of carbohydrate at a rate the body can use.

Related Terms: Multiple transportable carbohydrates, Carbohydrate concentration, Glucose, Fructose, Maltodextrin