The effects of a commercial dietary supplement on human performance

Twenty male runners were recruited to test whether a commercial ergogenic supplement was of any physiological benefit to endurance performance. Either a placebo or the supplement (a vitamin, mineral, amino acid, and unsaturated fatty acid complex) was administered to the subjects in a dose of three capsules daily over a 4-wk period in a double-blind design. A 60-min submaximal treadmill run (65 to 70% VO2 max) and a max VO2 test were completed by each subject before and after supplementation. The results demonstrated that even though exercise caused a significant decrease in muscle glycogen (36 to 48%) and blood glucose (24 to 34%) levels and an increase in blood free fatty acid (350%) and lactate concentration (200 to 230%), these changes were similar for both placebo and supplement groups. Similarly, the supplement had no effect on maximum oxygen consumption. We conclude that the supplement had no beneficial effect on performance as indicated by its inability to alter significantly any of the metabolic or physiological parameters, and that supplements of this nature are of no physiological value to the athlete who consumes a normal nutritionally balanced diet.