Dietary antioxidant restriction affects the inflammatory response in athletes.

The purpose of the present study was to determine the effects of dietary antioxidant restriction on plasma concentrations of carotenoids and inflammatory markers at rest and in response to exercise in endurance-trained males. Seventeen males performed two exercise trials 2 weeks apart. Participants followed their habitual antioxidant diet (H-AO) before the first exercise test, then a restricted antioxidant diet (R-AO) for 2 weeks before the second exercise test. Blood was collected pre- and post-exercise. Dietary intakes of fibre, ascorbic acid and beta-carotene were lower (P < 0.05) on the R-AO diet, but no other differences were observed. Pre-exercise plasma beta-carotene concentrations were lower (H-AO, 195 (sd 92); R-AO, 123 (sd 54) ng/ml; P < 0.05), and TNF-alpha concentrations were higher (H-AO, 16 (sd 7); R-AO, 613 (sd 325) pg/ml; P < 0.01) on the R-AO diet compared to the H-AO diet. Most plasma carotenoid concentrations decreased with exercise, but this effect was more consistent on the H-AO diet. No differences in plasma IL-6 concentrations were observed pre-exercise, whereas post-exercise plasma IL-6 concentrations (H-AO, 30.3 (sd 16); R-AO, 15.3 (sd 5) pg/ml; P < 0.05) were lower following the R-AO diet. Post-exercise TNF-alpha concentrations were higher on the R-AO diet. Ratings of perceived effort during submaximal exercise were higher (P < 0.05) on the R-AO diet, but there was no difference in the time to exhaustion between diets. In conclusion, lower dietary intakes of carotenoids alter the plasma concentrations of antioxidants and markers of inflammation at rest and in response to exercise.

Oxidative stress and antioxidants in athletes undertaking regular exercise training.

Exercise has been shown to increase the production of reactive oxygen species to a point that can exceed antioxidant defenses to cause oxidative stress. Dietary intake of antioxidants, physical activity levels, various antioxidants and oxidative stress markers were examined in 20 exercise-trained "athletes" and 20 age- and sex-matched sedentary "controls." Plasma F2-isoprostanes, antioxidant enzyme activities, and uric acid levels were similar in athletes and sedentary controls. Plasma alpha-tocopherol and beta-carotene were higher in athletes compared with sedentary controls. Total antioxidant capacity tended to be lower in athletes, with a significant difference between male athletes and male controls. Dietary intakes of antioxidants were also similar between groups and well above recommended dietary intakes for Australians. These findings suggest that athletes who consume a diet rich in antioxidants have elevated plasma alpha-tocopherol and beta-carotene that were likely to be brought about by adaptive processes resulting from regular exercise.

Antioxidant-restricted diet reduces plasma nonesterified fatty acids in trained athletes.

Nonesterified FA (NEFA) are a major fuel source for humans at rest and during moderate exercise. The effect of dietary antioxidant restriction on plasma NEFA levels and exercise performance in trained athletes was examined. Seventeen athletes followed a 2-wk restricted-antioxidant (R-AO) diet, which resulted in a threefold reduction in antioxidant intake (ascorbic acid, 139 to 49 mg; beta-carotene, 5093 to 1142 microg) and a significant (P = 0.001) reduction in the plasma NEFA. The amount and types of fat consumed were not different between the R-AO and habitual diets. Exercise time to exhaustion was not affected by the R-AO diet, but rating of perceived exertion (RPE) was significantly (P = 0.03) elevated. The increase in RPE may have occurred as a result of the R-AO diet and subsequent reduction in plasma NEFA; however, further research is required to confirm this conclusion.

Antioxidant restriction and oxidative stress in short-duration exhaustive exercise.

PURPOSE: To determine the effect of dietary antioxidant restriction on oxidative stress, antioxidant defenses, and exercise performance in athletes. Oxidative stress has been shown to increase during exercise. To alleviate oxidative stress, a high intake of antioxidant rich foods or supplements may be required in trained athletes. METHODS: Plasma oxidative stress and antioxidant defenses were examined in 17 trained athletes who underwent two separate exercise tests. Before the initial exercise test participants followed their habitual (high) antioxidant (H-AO) diets. Then they followed a 2-wk restricted-antioxidant (R-AO) diet before the second exercise test. Blood was taken at rest, after submaximal and high-intensity exhaustive exercise, and after 1 h of recovery. RESULTS: The R-AO diet induced a threefold reduction in antioxidant intake when compared with habitual-antioxidant (H-AO) diets. F(2)-isoprostane concentration (marker of oxidative stress) was significantly higher after submaximal exercise (38%), exhaustion (45%), and 1 h of recovery (31%) when following the R-AO diet compared with the H-AO diet. Rate of perceived exertion was increased on the R-AO diet whilst exercise time to exhaustion was not affected. Total antioxidant capacity and circulating antioxidant concentrations, although not significantly different, tended to be lower when following the R-AO diet. CONCLUSION: Athletes regularly participating in up to 40 min of acute high-intensity exercise may require higher intakes of exogenous antioxidants to defend against increased oxidative stress during exercise, which can be met through an adequate intake of high-antioxidant foods. Thus, there seems no valid reason to recommend antioxidant supplements to athletes participating in acute high-intensity exercise events up to 40 min in duration, except in those known to be consuming a low-antioxidant diet for prolonged periods.