Some athletes take fructose tablets during exercise. Since fructose has a low glycemic index (it causes a weaker reaction of blood glucose and insulin), athletes can mistakenly consider it to be the best source of energy.
Murrey et al. Studied the physiological, sensory responses and performance indicators for taking 6% solutions of glucose, sucrose and fructose during exercise. Levels of insulin in the blood, as expected, were lower when taking fructose. But fructose was associated with large gastrointestinal disorders, stronger stress and higher levels of serum cortisol, indicating greater physiological stress than glucose and sucrose. The time shown in the bicycle race with the intake of sucrose and glucose was also significantly higher than when taking fructose.
The lower level of glucose in the blood, associated with the intake of fructose, explains why the indices are not improving. The metabolism of fructose occurs predominantly in the liver, where it is converted into glycogen. Perhaps fructose can not turn into glucose and release quickly enough to supply the working muscles with adequate energy. In contrast, blood glucose levels are maintained or increased by the consumption of glucose, sucrose or glucose polymers. It is shown that they improve performance and are the preferred carbohydrates for sports drinks.
More frequent cases of gastrointestinal disorders (bloating, spasms and diarrhea), caused by the intake of large amounts of fructose, can be explained by slower absorption of fructose compared with glucose.
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