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Effect of a Ketogenic Diet on Submaximal Exercise Capacity and Efficiency in Runners

SHAW, DAVID M.1; MERIEN, FABRICE2; BRAAKHUIS, ANDREA3; MAUNDER, ED1; DULSON, DEBORAH K.1

Medicine & Science in Sports & Exercise: October 2019 - Volume 51 - Issue 10 - p 2135–2146
doi: 10.1249/MSS.0000000000002008
APPLIED SCIENCES
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Purpose We investigated the effect of a 31-d ketogenic diet (KD) on submaximal exercise capacity and efficiency.

Methods A randomized, repeated-measures, crossover study was conducted in eight trained male endurance athletes (V˙O2max, 59.4 ± 5.2 mL⋅kg−1⋅min−1). Participants ingested their habitual diet (HD) (13.1 MJ, 43% [4.6 g⋅kg−1⋅d−1] carbohydrate and 38% [1.8 g⋅kg−1⋅d−1] fat) or an isoenergetic KD (13.7 MJ, 4% [0.5 g·kg−1⋅d−1] carbohydrate and 78% [4 g⋅kg−1⋅d−1] fat) from days 0 to 31 (P < 0.001). Participants performed a fasted metabolic test on days −2 and 29 (~25 min) and a run-to-exhaustion trial at 70% V˙O2max on days 0 and 31 following the ingestion of a high-carbohydrate meal (2 g⋅kg−1) or an isoenergetic low-carbohydrate, high-fat meal (<10 g CHO), with carbohydrate (~55 g⋅h−1) or isoenergetic fat (0 g CHO⋅h−1) supplementation during exercise.

Results Training loads were similar between trials and V˙O2max was unchanged (all, P > 0.05). The KD impaired exercise efficiency, particularly at >70% V˙O2max, as evidenced by increased energy expenditure and oxygen uptake that could not be explained by shifts in respiratory exchange ratio (RER) (all, P < 0.05). However, exercise efficiency was maintained on a KD when exercising at <60% V˙O2max (all, P > 0.05). Time-to-exhaustion (TTE) was similar for each dietary adaptation (pre-HD, 237 ± 44 vs post-HD, 231 ± 35 min; P = 0.44 and pre-KD, 239 ± 27 vs post-KD, 219 ± 53 min; P = 0.36). Following keto-adaptation, RER >1.0 vs <1.0 at V˙O2max coincided with the preservation and reduction in TTE, respectively.

Conclusion A 31-d KD preserved mean submaximal exercise capacity in trained endurance athletes without necessitating acute carbohydrate fuelling strategies. However, there was a greater risk of an endurance decrement at an individual level.

1Sports Performance Research Institute New Zealand (SPRINZ), Auckland University of Technology, Auckland, NEW ZEALAND

2AUT-Roche Diagnostics Laboratory, School of Science, Auckland University of Technology, Auckland, NEW ZEALAND

3Faculty of Medical and Health Sciences, University of Auckland, Auckland, NEW ZEALAND

Address for correspondence: David Shaw, B.Sc., M.Diet., Sports Performance Research Institute New Zealand (SPRINZ), Auckland University of Technology, Auckland, New Zealand; E-mail: nutrition@daveshaw.co.nz.

Submitted for publication December 2018.

Accepted for publication April 2019.

Supplemental digital content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal’s Web site (www.acsm-msse.org).

Online date: April 26, 2019

© 2019 American College of Sports Medicine