Seven days of oral taurine supplementation does not increase muscle taurine content or alter substrate metabolism during prolonged exercise in humans

This study examined 1) the plasma taurine response to acute oral taurine supplementation (T), and 2) the effects of 7 days of T on muscle amino acid content and substrate metabolism during 2 h of cycling at ∼60% peak oxygen consumption (V̇o2peak). In the first part of the study, after an overnight fast, 7 volunteers (28 ± 3 yr, 184 ± 2 cm, 88.0 ± 6.6 kg) ingested 1.66 g oral taurine doses with breakfast (8 AM) and lunch (12 noon), and blood samples were taken throughout the day. In the second part of the study, eight men (22 ± 1 yr, 181 ± 1 cm, 80.9 ± 3.8 kg, 4.21 ± 0.16 l/min V̇o2peak) cycled for 2 h after 7 days of placebo (P) ingestion (6 g glucose/day) and again following 7 days of T (5 g/day). In the first part of the study, plasma taurine was 64 ± 4 μM before T and rose rapidly to 778 ± 139 μM by 10 AM and remained elevated at noon (359 ± 56 μM). Plasma taurine reached 973 ± 181 μM at 1 PM and was 161 ± 31 μM at 4 PM. In the second part of the study, seven days of T had no effect on muscle taurine content (mmol/kg dry muscle) at rest (P, 44 ± 15 vs. T, 42 ± 15) or after exercise (P, 43 ± 12 vs. T, 43 ± 11). There was no difference in muscle glycogen or other muscle metabolites between conditions, but there were notable interaction effects for muscle valine, isoleucine, leucine, cystine, glutamate, alanine, and arginine amino acid content following exercise after T. These data indicate that 1) acute T produces a 13-fold increase in plasma taurine concentration; 2) despite the ability to significantly elevate plasma taurine for extended periods throughout the day, 7 days of T does not alter skeletal muscle taurine content or carbohydrate and fat oxidation during exercise; and 3) T appears to have some impact on muscle amino acid response to exercise.