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Table 2 Study outcomes: VO2 max and secondary outcomes. Dashes indicate that studies did not assess the specified variable(s)

From: A review of the ketogenic diet for endurance athletes: performance enhancer or placebo effect?

ReferenceVO2 max outcomes (mL/kg/min)Time to exhaustion (TTE)Race time/Time trialRating of perceived exertion (RPE)Peak power
Prospective Trials
Burke et al. 2017 [12]Significant increase in VO2max from baseline (p < 0.001) in all three groups. VO2 Max of the HCD group was significantly lower than for the other groups both pre- and post-diet (p ≤ 0.02).
Pre- vs. post-intervention
EAKD: 66.3 vs. 71.1
HCD: 61.6 vs. 66.2
PCHO: 64.9 vs. 67.0
_ _EAKD group: Non-significant increase in 10 km race time from baseline.
HCD and PCHO groups: Significant decrease in race time (p < 0.01).
Pre- vs. post-intervention
EAKD: 23 s slower
HCD: 190 s faster
PCHO: 124 s faster
EAKD group: Significantly higher RPE values for post-intervention graded economy test compared with pre-intervention RPE values (p ≤ 0.01). Non-significant trend for higher RPE values during 25 km long walk for both pre- and post-testing._ _
Carr et al. 2018 [7]Significant increase in VO2max from baseline (p < 0.05) in all three groups. Between groups analysis not reported.
Pre- v. post-intervention (M ± SD)
EAKD: 61.1 ± 5.3 vs. 63.4 ± 4.1
HCD: 57.6 ± 4.6 vs. 58.3 ± 4.1
PCHO: 58.1 ± 3.3 vs. 60.2 ± 3.8
_ __ __ __ _
Heatherly et al. 2018 [13]Post-EAKD VO2 max not measured. Study reported % baseline VO2 max at various race paces. At 10 km, 21 km, 42 km and sub-42 km (but not 5 km) race paces, % relative VO2max was significantly greater post-EAKD.
Example (10 km pace; p < 0.05):
EAKD: 98.7 ± 11.3
HCD: 92.8 ± 5.3
_ _5 km time trial time was not significantly different pre- vs. post-EAKD (p > 0.10).
Pre- vs. post-intervention
EAKD: 23.45 ± 2.25 min.
HCD: 23.92 ± 2.57 min.
Overall RPE did not differ significantly pre- vs. post-EAKD during 5 km time trial (P > 0.10).
Pre- vs. post-intervention
EAKD: 8.4 ± 1.2
HCD: 8.0 ± 1.0
_ _
McSwiney et al. 2018 [14]Increase in both groups post-diet. Non-significant difference between groups (p = 0.968).
Pre- vs. post-intervention
EAKD: 53.6 ± 6.8 vs. 57.3 ± 6.7
HCD: 52.6 ± 6.4 vs. 57.2 ± 6.1
_ _100 km time trial time was not significantly different between groups (p = 0.057).
Pre- vs. post-intervention
EAKD: 4.07 min.sec faster
HCD: 1.13 min.sec faster
_ _Post-intervention peak power was significantly different between groups (p = 0.047).
Pre- vs. post-intervention
EAKD: 8.3 ± 2.2 vs. 9.7 ± 2.3; 1.4 watts/kg increase
HCD: 9.1 ± 2.6 vs. 8.4 ± 2.2; 0.7 watts/kg decrease
Phinney et al. 1983 [15]Non-significant decrease from baseline (HCD; p > 0.01).
Pre- vs. post-intervention
EAKD: 5.00 ± 0.20
HCD: 5.10 ± 0.18
Non-significant increase in mean exercise times from baseline (HCD).
Pre- vs. post-intervention
EAKD: 151 ± 25 min.
HCD: 147 ± 13 min.
_ __ __ _
Shaw et al. 2019 [16]No significant change from pre-intervention levels for either dietary exposure (p > 0.05).
Pre-intervention (all athletes)
59.4 ± 5.2
No significant difference between dietary interventions (p = 0.56).
Pre- vs. post-intervention
EAKD: 239 ± 27 vs. 219 ±
53 min. (p = 0.36)
HCD: 237 ± 44 vs. 231 ± 35 min. (p = 0.44)
_ _RPE values were similar for each dietary intervention during run-to-exhaustion trials.
1-h, 2-h, at exhaustion
EAKD: 11.4 ± 0.9, 12.1 ± 1.4, 19.38 ± 0.52
HCD: 11.7 ± 0.8, 12.8 ± 0.9, 19.38 ± 0.52
_ _
Case studies
Zinn et al. 2017 [17]Non-significant change from baseline (M ± SD): − 1.69 ± 3.4 (p = 0.63).
(with a decrease in four of the five athletes)
Significant decrease in TTE for all participants (p = 0.004).
Mean change from baseline
EAKD: − 2 ± 0.7 min.
_ __ _Four out of five athletes experienced a decrease in peak power from baseline (p = 0.07).
Mean change from baseline
EAKD: − 18 ± 16.4 watts
  1. EAKD Endurance Athlete Ketogenic Diet, HCD High Carbohydrate Diet, PCHO Periodised carbohydrate diet