Abstract
Consuming carbohydrate- and antioxidant-rich fruits during exercise as a means of supporting and enhancing both performance and health is of interest to endurance athletes. Watermelon (WM) contains carbohydrate, lycopene, l-citrulline, and l-arginine. WM may support exercise performance, augment antioxidant capacity, and act as a countermeasure to exercise-induced inflammation and innate immune changes. Trained cyclists (n = 20, 48 ± 2 years) participated in a randomized, placebo controlled, crossover study. Subjects completed two 75 km cycling time trials after either 2 weeks ingestion of 980 mL/day WM puree or no treatment. Subjects drank either WM puree containing 0.2 gm/kg carbohydrate or a 6% carbohydrate beverage every 15 min during the time trials. Blood samples were taken pre-study and pre-, post-, 1 h post-exercise. WM ingestion versus no treatment for 2-weeks increased plasma l-citrulline and l-arginine concentrations (p < 0.0125). Exercise performance did not differ between WM puree or carbohydrate beverage trials (p > 0.05), however, the rating of perceived exertion was greater during the WM trial (p > 0.05). WM puree versus carbohydrate beverage resulted in a similar pattern of increase in blood glucose, and greater increases in post-exercise plasma antioxidant capacity, l-citrulline, l-arginine, and total nitrate (all p < 0.05), but without differences in systemic markers of inflammation or innate immune function. Daily WM puree consumption fully supported the energy demands of exercise, and increased post-exercise blood levels of WM nutritional components (l-citrulline and l-arginine), antioxidant capacity, and total nitrate, but without an influence on post-exercise inflammation and changes in innate immune function.
Highlights
The importance of ingesting carbohydrate to maintain blood glucose levels during prolonged, vigorous exercise was recognized at the Boston Marathon in the early 1920s [1,2]
The consumption of multiple transportable carbohydrates during exercise improves the rate of carbohydrate oxidation [7], due to absorption of the carbohydrates by multiple transporters including the sodium-glucose transporter 1 (SGLT1), the universal glucose and fructose transporter (GLUT2), and the fructose transporter (GLUT5) [8]
The volume of WM puree consumed during the trial did not differ from volume of CHO beverage consumed (2.98 ± 0.17 L, 2.86 ± 0.16 L; p = 0.098)
Summary
The importance of ingesting carbohydrate to maintain blood glucose levels during prolonged, vigorous exercise was recognized at the Boston Marathon in the early 1920s [1,2]. The consumption of multiple transportable carbohydrates (e.g., a mixture of glucose and fructose) during exercise improves the rate of carbohydrate oxidation [7], due to absorption of the carbohydrates by multiple transporters including the sodium-glucose transporter 1 (SGLT1), the universal glucose and fructose transporter (GLUT2), and the fructose transporter (GLUT5) [8]. Data support the use of solutions with a fructose:glucose ratio of 0.8:1 and a consumption rate up to 1.7 g/min [9] to support performance. Consumption of fruit and fruit juice during endurance exercise as a means of sustaining performance and health is of interest to those desiring natural sources of exogenous carbohydrate. Use of raisins (fructose:glucose ratio of 1.1:1) as the carbohydrate source before and during exercise produced greater rates of carbohydrate oxidation and performance compared to water only [10]
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