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How To Use Carbohydrates for Energy: Glucose, Fructose and Maltodextrin

We all know that consuming carbohydrates for energy is a natural and essential part of sports nutrition but it’s important to know that not all carbohydrates are created equal, and your performance will likely suffer if you don’t choose the right source.

Carbohydrate depletion and dehydration and are the most likely causes of fatigue for endurance athletes during exercise lasting more than 60 minutes. It stands to reason, then, that ingesting carbohydrate during exercise will likely increase your time to exhaustion. Take onboard the right carbohydrate source, however, and you’ll likely improve your performance.

Recommended carbohydrate intake according to exercise length:

  • 60-90min of exercise > ingest 30g plus carbohydrates p/h
  • 90-120min of exercise > ingest 60g plus carbohydrates p/h
  • 2 hours or more of exercise > ingest 90g plus carbohydrates p/h

Fast and slow carbohydrates

One of the most important things to know about carbohydrates is that they differ vastly in their absorption rates and are typically differentiated between fast and slow carbohydrates:


The higher the glycemic index (GI) of a food, the quicker it passes through the digestive system and enters the bloodstream, prompting a faster insulin response and therefore faster glycogen resynthesis. As a result, our body can use the intake of carbohydrates such as glucose and maltodextrin almost instantly.


While glucose and maltodextrin both have a high glycemic index (GI of glucose is 100 and maltodextrin´s GI is even higher, at round 105-185), fructose is a slow carbohydrate with a low GI of around 23. Fructose must be digested, absorbed, and then processed by the liver before it is usable by our muscles to produce energy.

Choosing the right formulation

As well as their speed of absorption, fast and slow carbohydrates use different transporters into the muscle cells, where our body ultimately uses them for energy. These transport mechanisms often limit the amount of carbohydrates we can use; the transporter of slow carbohydrates is saturated at around 30g of carbohydrates per hour, whereas the transporter of fast carbohydrates is saturated at around 60g per hour.

This is why, during endurance events lasting more than two hours, we can use more carbohydrates per hour by combining a mixture of fast carbohydrates (like maltodextrin or glucose) and slow carbohydrates (like fructose) such as SiS Energy Bakes in a composition of 2:1 to optimise our performance.

Furthermore, current research shows that consuming maltodextrin and fructose in a 1:0.8 ratio such as SiS Beta Fuel further increases carbohydrate uptake.

Choose maltodextrin to avoid gastrointestinal discomfort

Simple sugars potentially have a higher risk of causing gastrointestinal discomfort since gut bacteria feed off simple sugars, which can lead to gas and bloating. Unlike longer chain molecules like maltodextrin, which form the basis of all SIS products, simple sugars like glucose and fructose are short molecules with a higher osmolality and require a larger quantity of water to make them isotonic (isotonic = containing the same particular concentration than blood). As water is retained with them when the stomach is emptied, simple sugars have a higher risk of stomach upset.

Maltodextrin is an isotonic formulation. Gastric emptying is maximised to deliver energy quickly with only minimal risk of gastric distress. At Science in Sport, we select a very specific type of maltodextrin for our Energy Gels, which have an atomic weight of 52,000 to allow us to create a unique and patented isotonic gel formulation. With an osmolality of 281 mmol/kg, they sit well within the isotonic range (beverages with an osmolality of under 290 mmol/kg are most easily digestible).

Tip: Always experiment with energy products in training or at a minor event before consuming them on your key event. Learn how your body reacts to them by using products under the same conditions as you will on race day.


  • Up to 2 hours of exercise > use fast carbohydrates like maltodextrin such as a GO Isotonic Energy Gel
  • Over 2 hours of exercise > combine fast carbohydrates like maltodextrin with slow carbohydrates like fructose such as Energy Bakes and all Beta Fuel products



Jeukendrup, A. E. (2011). Nutrition for endurance sports: Marathon, triathlon, and road cycling. Food, Nutrition and Sports Performance III, 29, 91–99.

O’Brien, W. J., Stannard, S. R., Clarke, J. A., & Rowlands, D. S. (2013). Fructose-maltodextrin ratio governs exogenous and other cho oxidation and performance. Medicine and Science in Sports and Exercise, 45(9), 1814–1824.

Stellingwerff, T., & Cox, G. R. (2014). Systematic review: Carbohydrate supplementation on exercise performance or capacity of varying durations. Applied Physiology, Nutrition and Metabolism, 39(9), 998–1011.

Written By

Lynn Starke

Lynn is a M.Sc. Sport nutrition student at Liverpool John Moores University and involved in current research projects conducted at LJMU. She received her Bachelor of Sport and Performance from the German Sport University Cologne where she focussed on the effects of food ingredients and nutritional supplements on physiological regeneration after high-intensity exercise. Parallel to her university and research activities, Lynn actively performs Olympic Weightlifting and CrossFit and has extensive experience as personal and group fitness coach.