Fructose

Fructose is a simple sugar with the same chemical formula as glucose (C6H12O6) but a different structure. It occurs naturally in fruits, honey and some root vegetables and tastes much sweeter than glucose. In sports drinks it is used alongside glucose to increase carbohydrate absorption.

Explanation

Unlike glucose, which is absorbed via the sodium‑glucose cotransporter SGLT1, fructose enters the bloodstream through the GLUT5 transporter. This separate pathway means that consuming fructose in addition to glucose can raise total carbohydrate uptake and oxidation beyond the limit of glucose alone. Fructose is metabolised primarily in the liver, where it is converted to glucose or stored as glycogen. Because it has a lower glycaemic index than glucose, fructose causes a smaller rise in blood sugar. However, large amounts of fructose consumed on its own can lead to gastrointestinal discomfort, as its transporter has limited capacity and unabsorbed fructose draws water into the intestine. For this reason, sports drinks typically include fructose at a lower proportion, often two parts glucose to one part fructose, to enhance absorption without exceeding the gut’s tolerance.

Fructose in sports drinks

A typical endurance beverage might contain 6 % carbohydrate with about one third of that coming from fructose. For example, a drink with 40 g of glucose and 20 g of fructose per litre delivers 60 g/h when consumed at one litre per hour. This combination increases exogenous carbohydrate oxidation to around 1.5 g/min while reducing the risk of stomach upset. Fructose is also present in natural sources such as fruit juice concentrates used to sweeten some drinks. Athletes should be cautious about consuming large amounts of pure fructose, as doses above 30 g per hour may cause bloating or diarrhoea. Pairing fructose with glucose and drinking small, frequent sips helps the gut handle it more comfortably.

Fructose adds sweetness and a complementary absorption pathway to sports drinks. Used in moderation alongside glucose, it can improve energy delivery and endurance without overloading the digestive system.

Related Terms: Glucose, Sucrose, Multiple transportable carbohydrates, Carbohydrate concentration, Exogenous carbohydrate oxidation