From: A review of the ketogenic diet for endurance athletes: performance enhancer or placebo effect?
Reference | Sample size | Population, age range | Study design | Study length | Methods | ||||
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Diet composition | Diet provision & assessment | Ketosis biomarker | Training protocol | VO2 Max protocol | |||||
Prospective trials | |||||||||
Burke et al. 2017 [12] | N = 29 | Professional male race walkers with international race experience, 21–32 years | Self-selected diet (non-random assignment) | 3 weeks | Diets:EAKD (< 50 g CHO, 75–80% FAT, 15–20% PRO [n = 10])a; HCD (60–65% CHO, 20% FAT, 15–20% PRO [n = 9])a; PCHO (60–65% CHO, 20% FAT, 15–20% PRO [n = 10])a | Personalized menus developed by professional chef and RDs. All foods provided/recorded by research team. | Beta-hydroxybutyrate levels post-EAKD: 0.8–2.0 mmol/liter | Olympic-level training camp. Included daily race walking, resistance training, and/or cross training. | Treadmill test |
Carr et al. 2018 [7] | N = 24 | Male (n = 17) and female (n = 7) elite race walkers | Self-selected diet (non-random assignment) | 3 weeks | Diets:EAKD (< 50 g CHO, 75–80% FAT, 15–20% PRO [n = 9]); HCD (60–65% CHO, 20% FAT, 15–20% PRO [n = 8]); PCHO (60–65% CHO, 20% FAT, 15–20% PRO [n = 7]) | Menus developed by professional chef and RDs. All foods provided/recorded by research team. | Elevated serum ketone bodies post-EAKD: 1 mmol/liter | Supervised, sport-specific, 3-week training protocol. | Treadmill test |
Heatherly et al. 2018 [13] | N = 8 | Middle-age, recreationally competitive male runners, 39.5 ± 9.9 years | Pre-posttest | 3 weeks | Diets:EAKD (< 50 g CHO, target 70% FAT [ad libitum]); HCD (habitual pre-study diet, reported as “moderate to high CHO”) | Participants provided with daily macronutrient targets and instructed to self-track diet using diet software. | Elevated serum ketone bodies post-dietary intervention compared to pre-EAKD levels: 0.7 ± 0.52 mmol/liter (EAKD) vs. 0.25 ± 0.09 mmol/liter (CHO) | Participants continued normal recreational athletic activity for study duration. | Treadmill test (pre-EAKD only). % baseline VO2 max at various race paces post-EAKD reported. |
McSwiney et al. 2018 [14] | N = 20 | Male endurance trained athletes (e.g., triathlon, cycling, marathon, ultra-marathon), 18–40 years | Self-selected diet (non-random assignment) | 12 weeks | Diets:EAKD (< 50 g CHO, > 75% FAT, 10–15% PRO [n = 9]); HCD (65% CHO, 20% FAT, 14% PRO [n = 11]) | Participants received detailed handouts (e.g., example meal plans, shopping lists), nutrition counseling, and weekly check-ins. Weekly weighed food diary submitted. | Beta-hydroxybutyrate levels post-EAKD: 0.5 mmol/liter | ≥ 7h hours of endurance exercise and 2 strength training sessions per week. | Cycle ergometer test |
Phinney et al. 1983 [15] | N = 5 | Elite male cyclists, 20–30 years | Pre-posttest | 4 weeks | Diets:EAKD (< 20 g CHO, 85% FAT, 15% PRO); HCD (1.75 g PRO/kg/day, remainder as 66% CHO and 33% FAT)a | Participants received three meals per day. Portions were weighed and intake monitored. | Beta-hydroxybutyrate levels post-EAKD: 1.28 ± 0.35 mmol/liter | Participants were asked to continue normal training, monitored via daily diary. | Cycle ergometer test |
Shaw et al. 2019 [16] | N = 8 | Male endurance trained athletes (n = 2 marathoners, n = 4 ultra-marathoners, n = 2 triathletes), 29.6 ± 5.1 years | Randomized repeated measures crossover study | 31-days (4.5 weeks) per condition with a 14- to 21-day washout period | Diets:EAKD (< 50 g CHO, 75–80% FAT, 15–20% PRO); HCD (43% CHO, 38% FAT, 19% PRO)a | Participants received education session with RD, info booklet, personalized menu plan, meal/snack examples, and lifestyle advice. All had daily contact with a registered dietitian for monitoring. | Beta-hydroxybutyrate levels post-EAKD: ≥0.3 mmol/liter by day 3 and ≥ 0.5 mmol/liter by day 7 | Participants designed their own 28-day training plan (running and cycling) and were asked to replicate this during each dietary period. | Treadmill test |
Case studies | |||||||||
Zinn et al. 2017 [17] | N = 5 | Recreational athletes involved in competitive endurance sport for 5+ years, 49–55 years | Pilot case study, mixed methods research | 10 weeks | Diet:EAKD (< 50 g CHO, ad libitum FAT, 1.5 g/kg PRO [n = 5]) | Participants provided with daily macronutrient prescription and instructed to self-track diet using diet software. | Beta-hydroxybutyrate levels: 0.5–4.2 mmol/liter | Participants continued normal recreational athletic activity for study duration. | Cycle ergometer test |