The current interest in low carbohydrate high fat (LCHF) diets for sports performance is based on enthusiastic claims and testimonials rather than a strong evidence base. Although adaptation to a LCHF (whether ketogenic or not) increases the muscle’s capacity to utilize fat as an exercise substrate, there is no proof that this leads to a clear performance advantage. In fact, there is a risk of impairing the capacity for high intensity exercise. |
The current guidelines for carbohydrate intake in the athlete’s training diet appear to be poorly understood. Sports nutrition experts do not promote a “high carbohydrate diet” for all athletes. Rather, the evolving model is that athletes should follow an individualized approach, whereby carbohydrate intake is periodized throughout the training cycle according to the fuel needs of each workout, the importance of performing well in the session and/or the potential to amplify the adaptive response to exercise via exposure to low carbohydrate availability. There is a need for ongoing research and practice to identify a range of approaches to optimal training and competition diets according to the specific requirements of an event and the experience of the individual athlete. |
1 Introduction
2 Sports Performance: A Brief Overview of Fuel Systems
Issue | Current knowledge and guidelines |
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CHO intake in the training diet | Previous focus on ‘high-CHO diets’ should be replaced by consideration of ‘CHO availability’, in which the daily amount and timing of CHO intake is compared with muscle fuel cost of training: ‘high CHO availability’ = intake providing adequate fuel for training needs, while ‘low CHO availability’ = intake is likely to be associated with CHO depletion [53] |
Daily CHO intake should not be static but should be periodized across training microcycles and macrocycles according to fuel cost of training load and the importance of training with high CHO availability [53] | |
When workouts involve high-intensity/volume/quality/technique, the day’s eating patterns should provide high CHO availability [53] | |
When workouts involve exercise of lower intensity/quality, it is less important to follow patterns that achieve high CHO availability [53] | |
Issue | Strategy | Targeted event(s) | Current knowledge and guidelines |
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Optimizing competition performance by increasing fuel availability (especially to addressing the scenario of limited fuel availability) | Increasing muscle phosphocreatine stores to enhance recovery during period between repeated high-intensity intervals: creatine loading | Stop and go sports: e.g., team sports, racket sports | Likely to be effective in sports/positions in which gradual depletion of phosphocreatine stores is limiting to movement patterns [62] Recommended protocol [63]: Rapid loading: 5 days @ 20 g/day creatine in split doses Slow loading: 30 days @ 3 g/day Maintenance: 3 g/day |
Increasing muscle glycogen stores in day(s) prior to event: CHO loading | Prolonged sustained or intermittent sports (usually >90 min) in which muscle glycogen stores become depleted: e.g., marathon, cycling road races, mid-field positions in some team games | Likely to be effective if event would otherwise deplete muscle glycogen stores, leading to reduction in speed and distance covered [64] Recommended protocol [53]: 36–48 h @ 10–12 g/kg/day CHO + taper | |
Increase in muscle/liver glycogen in hours prior to event: pre-event meal | Prolonged sustained or intermittent sports (usually >45 min), especially where pre-exercise muscle/liver glycogen are not optimized by other strategies | Likely to be effective if intake increases CHO availability (increase in liver/muscle glycogen > increase in rate of CHO oxidation during exercise) especially in CHO-limited event [53, 65] Recommended protocol [53]: 1–4 g/kg CHO at 1–4 h pre-event | |
Increase in exogenous supply of CHO: intake of CHO just prior to and during event Not needed for metabolic effects in events of more than ~75 min, but may be useful for central effects in events greater than ~45 min | Prolonged sustained or intermittent sports (usually >75 min) in which additional fuel source can replace/spare otherwise limited muscle glycogen stores: e.g., marathon, cycling road races, triathlons, team and racket sports | Likely to be effective if intake provides a readily available CHO supply to the muscle, particularly if muscle glycogen becomes depleted. May also address CNS impairment in events or individuals in which reductions in blood glucose concentrations occur [24, 66] Recommended protocol [53]: 1–2.5 h: 30–60 g/h CHO, >2.5–3 h: up to 90 g/h CHO | |
Sustained high-intensity sports (45–75 min) not typically considered to be limited by muscle glycogen stores, e.g., cycling time trial, half marathon | Likely to be effective in enhancing pacing strategy via effect on ‘reward centers’ in brain [61, 67] Recommended protocol [53]: frequent exposure of mouth and oral cavity to CHO, including mouth rinse | ||
Increase in fatty acid availability: fasting or short-term (1–3 days) high-fat diet | Prolonged sustained or intermittent sports (usually >75 min) in which additional fuel source can replace/spare otherwise limited muscle glycogen stores: e.g., marathon, cycling road races, triathlon, team and racket sports | Typically unable to increase (and may even impair) exercise capacity/performance since enhanced fat oxidation is unable to compensate for low muscle glycogen stores | |
Increase in fatty acid availability: high-fat pre-event meal (+heparin) or intralipid infusion | No clear performance benefit despite increased fat oxidation. Use of intralipid infusions and heparin to ensure high fatty acid availability is not practical | ||
Increase in fatty acid availability: feeding of medium chain triglycerides during exercise | Typically unable to increase (and may even impair) exercise capacity/performance since the large amounts needed to impact fuel metabolism cause gut problems [68] |
Athletes and study design | LCHF adaptation protocol | Performance protocol | Nutritional status/strategies for performance | Performance advantage with LCHF |
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Pre 2006 | ||||
Well-trained cyclists [30] (n = 5 M) Crossover design with order effect (control diet first) | 7 days HC (57 % CHO) then 28 days LCHF (fat = 85 % E, CHO = <20 g/day) | Cycling; TTE at 60 % VO2max | Overnight-fasted + no CHO intake during exercise | No NS difference in TTE between trials (151 vs. 147 min for LCHF and HC). Group data skewed by one participant who increased time to fatigue by 156 % on LCHF trial (Fig. 1) |
Post 2006 | ||||
Moderately trained off-road cyclists [49] (n = 8 M) Crossover design | 28 days HC (CHO = 50 % E) LCHF (fat = 70 % E, CHO = 15 %)? truly ketogenic | Cycling; VO2max test | Not stated | No Mixed results, with small increase in VO2max (56 vs. 59.2 ml/kg/min for HC and LCHF, p < 0.01) but reduction in maximum workload (350 vs. 362 W, p = 0.037). Small favorable change in body composition with LCHF (loss of ~1.8 kg with body fat loss from 14.9 to 11.0 % BM, p < 0.01) |
Elite artistic gymnasts [50] (n = 8 M) Crossover design with order effect (control diet second) | 30 days HC (CHO = 47 % E, 3.9 g/kg) then 30 days LCHF (fat = 55 % E, CHO <25 g/day) (note protein = 40 % E + added supplements) | Strength exercises: squat jump, countermovement jump, push-ups, reverse grip chin test, legs closed barrier maximum test | Not stated | No No change in strength measurements across either dietary phase—therefore, no impairment of performance measures with LCHF diet. Small favorable change in body composition with LCHF (loss of ~1.5 kg with body fat loss from 7.6 to 5.4 % BM) |
3 Chronic Adaptation to High-Fat Diets: Research from 1980 to 2006
3.1 Ketogenic High-Fat Diets
3.2 Non-Ketogenic High-Fat Diets
Athletes | LCHF adaptation protocol | Performance protocol | Nutritional status/strategies for performance | Performance advantage with LCHF |
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Moderately trained cyclists [33] (n = 7 F) Crossover design | 7 days LCHF (fat = 59 % E, CHO = 1.2 g/kg BM) HC (CHO = 6.4 g/kg BM) | Cycling TTE at 80 % VO
2max | 3–4 h after meal, no CHO intake during exercise | No In fact, performance deteriorated with LCHF. Time to exhaustion reduced by 47 % on LCHF trial |
Well-trained cyclists [34] (n = 5 M) Crossover design | 14 days LCHF (fat = 67 % E, CHO = 17 % Ea) HC (CHO = 74 % Ea) | Cycling 30 s Wingate test + TTE at 90 % VO2max + TTE at 60 % VO
2max | Overnight-fasted + no CHO intake during exercise | No: two higher intensity tests Yes: Submaximal cycling Time to exhaustion increased by 87 % on LCHF trial commenced with lower glycogen stores due to preceding exercise |
Well-trained cyclists [35] (n = 16 M) Parallel-group design | 15 days LCHF (fat = 69 %E, CHO = 2.2 g/kg BM) HC (CHO = 5.5 g/kg BM) | Cycling 150 min at 70 % VO
2max + 40 km TT Performance measured at t = 0, 5, 10, and 15 days | MCT intake 1.5 h before event (~14 g) MCT (0.3 g/kg/h) and CHO (0.8 g/kg/h) during exercise | No TT performance increased over time in both groups as a result of training protocol. Significant improvements seen in both groups by day 10, but no difference in mean improvement between groups. Important finding of study: adaptations achieved after only 5 days of high-fat diet |
Well-trained cyclists [36] (n = 7 M) Crossover design | 14 days LCHF (fat = 66 % E, CHO = ~2.4 g/kg) HC (CHO = ~8.6 g/kg, 70 % CHO) | Cycling 5 h including 15 min TT + 100 km TT | LCHF = high-fat pre-event meal HC = high CHO pre-event meal Both: 0.8 g/kg/h CHO during ride | Yes: submaximal intensity exercise No: higher-intensity exercise Relative to baseline: HC showed small NS decreases in performance of both 15 min TT and 100 km TT LCHF showed larger but NS decrease in performance of 15 min TT but small NS improvement in 100 km TT |
Well-trained duathletes [37] (n = 11 M) Crossover design | 5 weeks LCHF (fat = 53 % E, CHO = ~3.6 g/kg) HC (CHO = ~6.9 g/kg, 68 % CHO) | Cycling 40 min incremental protocol + 20 min TT @ ~89 % VO
2max Running (separate day) Outdoor 21 km TT | LCHF = high-fat pre-event meal HC = high CHO pre-event meal Intake pre and during half marathon not stated | No Self-selected work output similar for cycling TT in both dietary treatments (298 ± 6 vs. 297 ± 7 W, NS) for LCHF and HC, respectively. Half marathon time not different between trials (80 min 12 s ± 86 s vs. 80 min 24 s ± 82 s, NS) |
3.3 Fat Adaptation and Carbohydrate Restoration
Participant characteristics | LCHF adaptation protocol | CHO restoration | Performance protocol | Nutritional status/strategies for performance | Performance advantage with LCHF adaptation + CHO restoration |
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Well-trained cyclists/triathletes [45] (n = 8 M) Crossover design | 5 days LCHF-adapt (fat = 68 % E; CHO = 18 % E, 2.5 g/kg BM) or HC (CHO = 74 % E, 9.6 g/kg BM CHO) | 1 day rest + high CHO (CHO = 75 % E, 10 g/kg BM) | Cycling 120 min at 70 % VO2max + ~30 min TT (time to complete 7 J/kg BM) | Fasted + no CHO intake during exercise | Perhaps for individuals Two participants performed badly on HC trial, probably because of hypoglycemia. Plasma glucose better maintained on LCHF-adapt trial. TT not significantly different between trials: 30.73 ± 1.12 vs. 34.17 ± 2.62 min for LCHF and HC trial. However, mean difference in TT = 8 % enhancement with LCHF trial (p = 0.21, NS; 95 % CI –6 to 21). |
Well-trained cyclists and triathletes [41] (n = 8 M) Crossover design | 5 days LCHF-adapt (fat = 68 % E; CHO = 18 % E, 2.5 g/kg BM) or HC (CHO = 70 % E, 9.3 g/kg BM CHO) | 1 day rest + high CHO (CHO = 75 % E, 10 g/kg BM) | Cycling 120 min at 70 % VO2max + ~30 min TT (time to complete 7 J/kg BM) | CHO intake 2 h before exercise (2 g/kg BM) and during exercise (0.8 g/kg/h) | No Plasma glucose maintained in both trials due to CHO intake during exercise. Difference in TT between trials was trivial: LCHF-adapt = 25.53 ± 0.67 min; HC = 25.45 ± 0.96 min (p = 0.86, NS). Mean difference in TT = 0.7 % impairment with LCHF-adapt trial (95 % CI –1.7 to 0.4) |
Highly-trained cyclists and triathletes [42] (n = 7 M) Crossover design | 6 days LCHF-adapt (fat = 69 % E CHO = 16 % E, 2.5 g/kg BM) or HC (CHO = 75 % E, 11 g/kg BM) | 1 day rest + high CHO (CHO = 75 % E, 11 g/kg BM) | Cycling 240 min at 65 % VO2max + 60 min TT (distance in 1 h) | CHO intake before exercise (3 g/kg BM) and during exercise (1.3 g/kg/h) | No or perhaps for individuals TT performance NS between trials: 44.25 ± 0.9 vs. 42.1 ± 1.2 km for LCHF-adapt and HC trial. However, mean difference in TT performance = 4 % enhancement with LCHF-adapt (p = 0.11, NS) (95 % CI –3 to 11) |
Highly-trained cyclists and triathletes [43] (n = 7 M) Crossover design | 5 days LCHF-adapt (fat = 69 % E CHO = 16 % E, 2.5 g/kg BM) or HC (CHO = 75 % E, 11 g/kg BM) | 1 day rest + high CHO (CHO = 75 % E, 11 g/kg BM) | Cycling 240 min at 65 % VO2max + 60 min TT (distance in 1 h) | CHO intake before exercise (3 g/kg BM) and during exercise (1.3 g/kg/h) | No Additional six subjects undertaken to test for Type 1 error in previous study [42]. TT performance NS between trials: 42.92 ± 1.46 vs. 42.94 ± 1.41 km for LCHF-adapt and HC trial (p = 0.98). Performance difference = 0.02 km or 0.1 % |
Trained cyclists and triathletes [44] (n = 5 M) Crossover design | 10 days LCHF-adapt (fat = 65 % E, CHO = 15 % E, 1.6 g/kg BM) or HC (CHO = 53 % E, 5.8 g/kg BM) | 3 days high CHO (CHO = 65 % E, 7 g/kg BM) + 1 day rest | Cycling 150-min cycling at 70 % VO2max + 20-km (~30 min) TT | MCT intake 1 h before event (~14 g); MCT (0.3 g/kg/h) and CHO (0.8 g/kg/h) during exercise | Yes Difference in TT performance = 4 % enhancement with LCHF-adapt: 29.35 ± 1.25 vs. 30.68 ± 1.55 min for LCHF-adapt and HC (p < 0.05) |
Well-trained cyclists [36] (n = 7 M) Crossover design | 11.5 days LCHF-adapt (~2.4 g/kg, 15 % CHO; 66 % fat) or HC (CHO = ~8.6 g/kg, 70 % E) | 2.5 days high CHO (6.8 g/kg BM) | Cycling 5-h protocol including 15-min TT + 100-km TT | HC: High-CHO pre-event meal Both: 0.8 g/kg/h CHO during exercise | Perhaps—submaximal intensity exercise No—higher-intensity exercise Relative to baseline testing: HC trial showed small NS decrease in performance of both 15-min TT and 100-km TT. LCHF-adapt showed no change in 15-min TT but small NS enhancement of 100-km TT |
Well-trained cyclists [1] (n = 8 M) Crossover design | 6 days LCHF-adapt (fat = 68 % E CHO = 17 % E, 1.8 g/kg BM) or HC (CHO = 68 % E, 7.5 g/kg BM) | 1 day rest + high CHO (8–10 g/kg) | Cycling 100 km TT, including 4 × 4-km sprints + 5 × 1-km sprints | CHO consumed during ride | No—in fact, performance enhancement of 1-km sprints Differences between 100-km TT performances: NS (156 min 54 s vs. 153 min 10 s for LCHF-adapt vs. HC). Difference between power output during 4-km sprints: NS. However, power during 1-km sprints (undertaken at >90 % PPO) was significantly reduced in LCHF-adapt trial |
3.4 Summary of Learnings from the Literature: 1999–2006
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Type II statistical error: failure to detect small but important changes in performance due to small sample sizes [34], individual responses [42, 45], and poor reliability of the performance protocol. While this explanation often looks attractive [43], in some cases, further exploration and enhanced sample size increases confidence in the true absence of a performance enhancement [43].
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Benefits are limited to specific scenarios: characteristics of conditions under which fat-adaptation strategies appear to be more likely to be beneficial include protocols of prolonged sub-maximal exercise in which pre-exercise glycogen is depleted and/or no carbohydrate is consumed during exercise (e.g., low-carbohydrate availability).
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Benefits are limited to specific individuals: characteristics of individuals who may respond to fat-adaptation strategies include carbohydrate-sensitive individuals who are subjected to scenarios in which carbohydrate cannot be consumed during exercise.
4 Update on Fat Adaptation Literature Since 2006
5 Summary and Future Directions
Scenarios favoring adaptation to LCHF diet | Other explanations for anecdotal reports of performance benefits from switching to LCHF diet |
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Individuals or events involving prolonged sub-maximal effort where there is no benefit or requirement for higher-intensity pieces Individuals or events in which it is difficult to consume adequate CHO to meet goals for optimal CHO availability (e.g., gastrointestinal upsets, logistical difficulties with accessing supplies during the event) Individuals who are carbohydrate sensitive and likely to be exposed to low CHO availability | Switch to LCHF has been associated with loss of body fat and increase in power-to-mass ratio Previous diet and training were sub-optimal, and switch has been associated with greater training and diet discipline Order effect: natural progress in training and maturation in age and sporting experience Previous program did not include accurate measurement of performance: awareness of performance metrics just commenced Placebo effect/excitement about being part of new idea/culture Athlete is not actually adhering to LCHF diet, due to misunderstanding of its true composition or own ‘tweaking’ activities, such that eating patterns include sufficient CHO around key training sessions and competition to promote high CHO availability |