Fructose, exercise, and health.

The large daily energy intake common among athletes can be associated with a large daily intake of fructose, a simple sugar that has been linked to metabolic disorders. Fructose commonly is found in foods and beverages as a natural component (e.g., in fruits) or as an added ingredient (as sucrose or high fructose corn syrup [HFCS]). A growing body of research suggests that excessive intake of fructose (e.g., >50 g.d(-1)) may be linked to development of the metabolic syndrome (obesity, dyslipidemia, hypertension, insulin resistance, proinflammatory state, prothrombosis). The rapid metabolism of fructose in the liver and resultant drop in hepatic adenosine triphosphate (ATP) levels have been linked with mitochondrial and endothelial dysfunction, alterations that could predispose to obesity, diabetes, and hypertension. However, for athletes, a positive aspect of fructose metabolism is that, in combination with other simple sugars, fructose stimulates rapid fluid and solute absorption in the small intestine and helps increase exogenous carbohydrate oxidation during exercise, an important response for improving exercise performance. Although additional research is required to clarify the possible health-related implications of long-term intake of large amounts of dietary fructose among athletes, regular exercise training and consequent high daily energy expenditure may protect athletes from the negative metabolic responses associated with chronically high dietary fructose intake.