There were differences ( p < 0.001 ) between the group fasted for 30 compared with 0 hours in mean concentrations of free fatty acids ( 0.98 ( SD 0.32 ) vs. 0.58 ( SD 0.23 ) mmol/L ) , - hydroxybutyrate ( 0.69 ( SD 0.17 ) vs. 0.42 ( SD 0.11 ) mmol/L ) , triglycerides ( 0.29 ( min 0.13 , max 0.83 ) vs. 0.22 ( min 0.06 , max 0.96 ) mmol/L ) and urea ( 10.17 ( SD 1.80 ) vs. 6.94 ( SD 2.03 ) mmol/L ) .