©Journal of Sports Science and Medicine (2018) 17, 259 - 268

Effects of a 4-Week Very Low-Carbohydrate Diet on High-Intensity Interval Training Responses

Lukas Cipryan1,, Daniel J. Plews2, Alessandro Ferretti3, Phil B. Maffetone4, Paul B. Laursen2

1Department of Human Movement Studies & Human Motion Diagnostic Centre, Ostrava University, Czech Republic 2Sport Performance Research Institute New Zealand (SPRINZ), Auckland University of Technology, Auckland, New Zealand 3Independent researcher, Stratford Upon Avon, United Kingdom 4Independent researcher, Arizona, USA

Lukas Cipryan
✉ Ostravska univerzita, CDLP, Varenska 40°, 702 00 Ostrava, Czech Republic
Email: lukas.cipryan@osu.cz

05-02-2018 -- Accepted: 29-03-2018 --
Published (online): 14-05-2018

The purpose of the study was to examine the effects of altering from habitual mixed Western-based (HD) to a very low-carbohydrate high-fat (VLCHF) diet over a 4-week timecourse on performance and physiological responses during high-intensity interval training (HIIT). Eighteen moderately trained males (age 23.8 ± 2.1 years) consuming their HD (48 ± 13% carbohydrate, 17 ± 3% protein, 35 ± 9% fat) were assigned to 2 groups. One group was asked to remain on their HD, while the other was asked to switch to a non-standardized VLCHF diet (8 ± 3% carbohydrate, 29 ± 15% protein, 63 ± 13% fat) for 4 weeks. Participants performed graded exercise tests (GXT) before and after the experiment, and an HIIT session (5x3min, work/rest 2:1, passive recovery, total time 34min) before, and after 2 and 4 weeks. Heart rate (HR), oxygen uptake (O2), respiratory exchange ratio (RER), maximal fat oxidation rates (Fatmax) and blood lactate were measured. Total time to exhaustion (TTE) and maximal O2 (V̇O2max) in the GXT increased in both groups, but between-group changes were trivial (ES ± 90% CI: -0.1 ± 0.3) and small (0.57 ± 0.5), respectively. Between-group difference in Fatmax change (VLCHF: 0.8 ± 0.3 to 1.1 ± 0.2 g/min; HD: 0.7 ± 0.2 to 0.8 ± 0.2 g/min) was large (1.2±0.9), revealing greater increases in the VLCHF versus HD group. Between-group comparisons of mean changes in V̇O2 and HR during the HIIT sessions were trivial to small, whereas mean RER decreased more in the VLCHF group (-1.5 ± 0.1). Lactate changes between groups were unclear. Adoption of a VLCHF diet over 4 weeks increased Fatmax and did not adversely affect TTE during the GXT or cardiorespiratory responses to HIIT compared with the HD.

Key words: High-intensity exercise, graded exercise test, ketosis, low-carbohydrate diet, high-fat diet

Key Points
A group of participants that changed from habitual mixed western-based to VLCHF diet over 4 weeks substantially increased rates of fat oxidation shown during a graded exercise test and high-intensity interval training (HIIT) session.
Performance and cardiorespiratory responses during a graded exercise test and HIIT were not impaired after consuming a VLCHF diet relative to a group consuming their mixed western-based diet.
A four-week adaptation period to a VLCHF diet preserved high-intensity exercise performance.