Elsevier

Metabolism

Volume 65, Issue 3, March 2016, Pages 100-110
Metabolism

Clinical Science
Metabolic characteristics of keto-adapted ultra-endurance runners

https://doi.org/10.1016/j.metabol.2015.10.028Get rights and content
Under a Creative Commons license
open access

Abstract

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.

Abbreviations

VO2max
maximal oxygen consumption
HC
high-carbohydrate
LC
low-carbohydrate
FASTER
Fat Adapted Substrate use in Trained Elite Runners
RPE
ratings of perceived exertion
DXA
dual-energy X-ray absorptiometry
RER
respiratory exchange ratio
USG
urine specific gravity
ELISA
enzyme-linked immunosorbent assay
NEFA
non-esterified fatty acid
HOMA
homeostatic model assessment of insulin resistance
IP
immediately post-exercise
PE-120
120 min post-exercise

Keywords

carbohydrate
fat
metabolism
exercise
glycogen