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Fructose during physical activity
Last reviewed: 08.07.2025
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Some athletes take fructose tablets during exercise. Because fructose has a low glycemic index (it causes a weaker blood glucose and insulin response), athletes may mistakenly believe it is a better source of energy.
Murrey et al. studied the physiological, sensory, and exercise performance responses to 6% glucose, sucrose, and fructose solutions during exercise. Blood insulin levels were lower with fructose, as expected. However, fructose was associated with greater gastrointestinal distress, greater tension, and higher serum cortisol levels, indicating greater physiological stress than glucose and sucrose. Cycling times were also significantly longer with sucrose and glucose than with fructose.
The lower blood glucose levels associated with fructose ingestion may explain why performance is not improved. Fructose is metabolized primarily in the liver, where it is converted to glycogen. It may be that fructose cannot be converted to glucose and released quickly enough to provide adequate energy to working muscles. In contrast, blood glucose levels are maintained or increased by ingesting glucose, sucrose, or glucose polymers. These have been shown to improve performance and are the carbohydrates of choice for sports drinks.
The increased incidence of gastrointestinal upset (bloating, cramping and diarrhea) caused by consuming large amounts of fructose may be explained by the slower absorption of fructose compared to glucose.
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