Phytonutrients from plant foods provide numerous antioxidants. We hypothesized that supplementation for 28 wk with a commercially available encapsulated juice powder concentrate (JPC) could influence indicators of oxidative stress, immunity, and illness. Trained men (n = 41; 34 +/- 5 y; maximum oxygen uptake = 55 +/- 7 mL x kg(-1) x min(-1)) from a homogenous police Special Forces unit were randomly assigned in a double blind manner to either JPC (n = 21) or placebo (n = 20). We used multiple 7-d food records to assess dietary intake and found inadequate mean daily fruit and vegetable consumption (3.2 +/- 1.2 servings). The group physician documented all duty days lost due to illness. We collected plasma at baseline and study wk 4, 8, 16, and 28 for analysis of carbonyl groups on protein (CP) and TNFalpha. Over the 28-wk investigation, CP was lower in the JPC group, with both a treatment and a time x treatment interaction (P < 0.05). Concentrations of both CP and TNFalpha at 16 and 28 wk were lower in the JPC than in the placebo group (P < 0.001). TNFalpha increased during the first 8 wk followed by a decrease in both groups for the following 20 wk (P < 0.001). Over the final 20 wk of the study, the placebo group tended to have more days of illness than the JPC group (P = 0.068). These data suggest beneficial JPC effects with regard to reduction of duty days lost due to illness and reduction of CP and TNFalpha concentrations in this group of trained men over 28 wk.