Metabolic characteristics of keto adapted ultra endurance runners.
BACKGROUND Many successful ultra endurance athletes have switched from a high carbohydrate to a low carbohydrate diet, but they have not previously been studied to determine the extent of metabolic adaptations. METHODS Twenty elite ultra marathoners and ironman distance triathletes performed a maximal graded exercise test and a 180 min submaximal run at 64% VO2max on a treadmill to determine metabolic responses. One group habitually consumed a traditional high carbohydrate (HC: n=10, %carbohydrate:protein:fat=59:14:25) diet, and the other a low carbohydrate (LC; n=10, 10:19:70) diet for an average of 20 months (range 9 to 36 months) RESULTS Peak fat oxidation was 2.3 fold higher in the LC group (1.54+ 0.18 vs 0.67+ 0.14 g/min; P=0.000) and it occurred at a higher percentage of VO2max (70.3+ 6.3 vs 54.9+ 7.8% P=0.000) Mean fat oxidation during submaximal exercise was 59% higher in the LC group (1.21+ 0.02 vs 0.76+ 0.11 g/min; P=0.000) corresponding to a greater relative contribution of fat (88+ 2 vs 56+ 8% P=0.000) Despite these marked differences in fuel use between LC and HC athletes, there were no significant differences in resting muscle glycogen and the level of depletion after 180 min of running 64% from pre exercise) and 120 min of recovery 36% from pre exercise) CONCLUSION Compared to highly trained ultra endurance athletes consuming an HC diet, long term keto adaptation results in extraordinarily high rates of fat oxidation, whereas muscle glycogen utilization and repletion patterns during and after a 3 hour run are similar.
Metabolism: clinical and experimental