Ketogenic low-CHO, high-fat diet: The future of elite endurance sport?

May combine two claims.

Retooling of the muscle can double exercise fat use to ∼1.5 g min−1, with the intensity of maximal rates of oxidation shifting from ∼45% to ∼70% of maximal aerobic capacity.

“Retooling of the muscle can double exercise fat use to ∼1.5 g min−1, with the intensity of maximal rates of oxidation shifting from ∼45% to ∼70% of maximal aerobic capacity.”

May combine two claims.

In Phinney et al. 1983, the key finding of maintained endurance masked a highly variable response to K-LCHF treatment, with the group average skewed by a substantial increase in exercise capacity in one individual.

“The key finding of maintained endurance, however, masked a highly variable response to K‐LCHF treatment (Fig. 1), with the group average skewed by a substantial increase in exercise capacity in one individual (Phinney et al. 1983).”

• cites Phinney et al. 1983Not checked yet

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In Zinn et al. 2014, there was a reduction in time to exhaustion, peak power and VO2peak.

“reduction in TTE, peak power and V˙O2peak”

• cites Zinn et al. (2014)Not checked yet

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In Zajak et al. 2014, there was a small increase in VO2peak but a reduction in maximum workload and workload at lactate threshold.

“Small increase in V˙O2peak (56 vs. 59.2 ml kg−1 min−1 and V˙O2 at ‘LT’ for HCHO and K‐LCHF, p < 0.01) but reduction in maximum workload (350 vs. 362 W, P = 0.037) and workload at ‘LT’”

• cites Zajak et al. (2014)Not checked yet

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In Prins et al. 2019, performance of the day 4 time trial was impaired in the K-LCHF trial compared with the HCHO trial (1231 s vs. 1182 s, p < 0.011), but there was no significant difference between performance on other days.

“Impaired performance of D4 TT in K‐LCHF trial compared with HCHO trial (1231 s vs. 1182 s, p < 0.011), but NS difference between performance on other days.”

• cites Prins et al. (2019)Not checked yet

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May combine two claims.

The replication study found an equivalent margin between pre- and post-study 10,000 m track races, approximately 7% difference between the HCHO and K-LCHF groups, with significant improvement of 4.8% and significant impairment of 2.3% of race times, respectively.

“An equivalent margin between the pre‐ and post‐study 10,000 m track races (∼7% difference between the HCHO and K‐LCHF groups, with significant improvement (4.8%) and significant impairment (2.3%) of race times, respectively; Burke et al. 2020)”

• cites Burke et al. 2020Not checked yet

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In Burke et al. 2020, HCHO improved performance by 4.8% (134 s faster) but K-LCHF was slower by 2.3% (86 s) (both P < 0.001).

“HCHO: improved performance by 4.8% (134 s faster) but K‐LCHF: slower by 2.3% (86 s) (both P < 0.001)”

• cites Burke et al. (2020)Not checked yet

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May combine two claims.

In the study, an increased absolute oxygen cost of exercise in the K-LCHF group negated the increase in V̇O2peak, leaving no net change in relative exercise economy.

“Meanwhile, an increased absolute oxygen cost of exercise in K‐LCHF group negated the increase in V˙O2peak, leaving no net change in relative exercise economy (see Fig. 2).”

May combine two claims.

In the study, following training, the HCHO group improved their relative economy because the oxygen cost of walking at race-speeds accounted for a lower percentage of their enhanced aerobic capacity.

“following training, the HCHO group improved their relative economy because the oxygen cost of walking at race‐speeds accounted for a lower percentage of their enhanced aerobic capacity.”

May combine two claims.

In McSwiney et al. 2018, K-LCHF significantly improved peak but not average power in 6 s and CPT; there was a trend to faster 100 km (166 ± 12.4 vs. 161.5 ± 8.4 min; 2.5%).

“K‐LCHF significantly improved peak but not average power in 6 s and CPT; trend to faster 100 km (166 ± 12.4 vs. 161.5 ± 8.4 min; 2.5%).”

• cites McSwiney et al. (2018)Not checked yet

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Studies of K-LCHF and endurance performance are sparse and heterogeneous in terms of athlete calibre, duration of adaptation and types of exercise protocol.

“Studies of K‐LCHF and endurance performance are sparse and heterogeneous in terms of athlete calibre, duration of adaptation and types of exercise protocol.”

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

A national record was broken by a large margin by one study participant 3 weeks after completing 24 days of keto-adaptation within the research project, creating social media speculation of similarities between K-LCHF diet and altitude training.

“Thus, a national record broken by a large margin by one study participant, 3 weeks after completing 24 days of keto‐adaptation within our research project, created social media speculation of similarities between K‐LCHF diet and altitude training, in creating a legacy of physiological changes that could integrate with the race taper and return to HCHO to enhance performance (Burke et al. 2020).”

• cites Burke et al. 2020Not checked yet

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Statistical normalisation of the 20 km race time suggested that K-LCHF-HCHO group had no improvement in performance over 6 weeks training (197 ± 6%) while CHO-HCHO had faster race time (191 ± 6%, P < 0.01).

“In fact, statistical normalisation of the 20 km race time suggested that K‐LCHF‐HCHO group had no improvement in performance over 6 weeks training (197 ± 6%) while CHO‐HCHO had faster race time (191 ± 6%, P < 0.01).”

• cites Burke et al. (2020)Not checked yet

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Additional testing during the race warm-up showed that K-LCHF was associated with higher rates of fat oxidation and only a partial restoration of CHO oxidation in Race 2, despite identical pre-race dietary preparation.

“Additional testing during the race warm‐up showed that K‐LCHF was associated with higher rates of fat oxidation and only a partial restoration of CHO oxidation in Race 2, despite identical pre‐race dietary preparation.”

• cites Burke et al. unpublished dataNot checked yet

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In the case study, exercise tests showed an apparent benefit to exercise reliant on CHO oxidation (higher intensity work of 30 s-20 min duration), but no effects on lower-intensity (<60-65% V ̇O2peak) and supra-maximal (> maximal aerobic capacity) exercise when CHO was consumed acutely around each test.

“A series of exercise tests at the end of each period, fuelled by the prevailing dietary strategy, showed an apparent benefit to exercise reliant on CHO oxidation (higher intensity work of 30 s–20 min duration), but no effects on lower‐intensity (<60–65% V˙O2peak) and supra‐maximal (> maximal aerobic capacity) exercise when CHO was consumed acutely aroud each test.”

• cites Webster et al. 2018Not checked yet

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All participants in the HCHO group recorded faster times in Race 2 with a mean improvement of 5.7%, while only one participant in the K-LCHF improved in the second race (mean = 2.1% impairment); this replicated a familiar experience of ∼8% difference in performance between K-LCHF and HCHO groups.

“Whereas all participants in the HCHO group recorded faster times in Race 2 with a mean improvement of 5.7%, only one participant in the K‐LCHF improved in the second race (mean = 2.1% impairment); this replicated our familiar experience of ∼8% difference in performance between K‐LCHF and HCHO groups (Burke et al. 2017, 2020).”

• cites Burke et al. 2017Not checked yet

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• cites Burke et al. 2020Not checked yet

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May combine two claims.

CHO intake during 100 km TT produced small increase in rates of CHO oxidation (0.7 g min−1 to max of ∼1 g min−1) while fat oxidation was reduced by ∼0.3 g min−1 to min of ∼1.2 g min−1.

“CHO intake during 100 km TT produced small increase in rates of CHO oxidation (0.7 g min−1 to max of ∼1 g min−1) while fat oxidation was reduced by ∼0.3 g min−1 to min of ∼1.2 g min−1).”

• cites Webster et al. (2018)Not checked yet

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Classified as probably not a substantial claim.

Periodisation of K-LCHF with high CHO availability might offer opportunities to restore capacity for higher-intensity exercise.

“Periodisation of K‐LCHF with high CHO availability might offer opportunities to restore capacity for higher‐intensity exercise”

Probably not a substantial claim: may not pass S3 (load-bearing).

Key characteristics of elite endurance athletes involve the interaction of high peak aerobic capacity, high muscle oxidative capacity and high exercise economy.

“Key characteristics of elite endurance athletes, accrued via genetics and training, involve the interaction of high peak aerobic capacity (V˙O2peak), high muscle oxidative capacity and high exercise economy (Joyner & Coyle, 2008).”

• cites Joyner & Coyle, 2008Not checked yet

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Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

These approaches support motor recruitment, pacing and perception of effort.

“and support motor recruitment, pacing and perception of effort (Burke & Maughan, 2015).”

• cites Burke & Maughan, 2015Not checked yet

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May combine two claims.

Keto-adaptation may impair the muscle's ability to use glycogen for oxidative fates, compromising the use of a more economical energy source when the oxygen supply becomes limiting and, thus, the performance of higher-intensity exercise (>80% maximal aerobic capacity).

“keto‐adaptation may impair the muscle's ability to use glycogen for oxidative fates, compromising the use of a more economical energy source when the oxygen supply becomes limiting and, thus, the performance of higher‐intensity exercise (>80% maximal aerobic capacity).”

Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based).

Even when such pieces make a small contribution to overall energy costs, they are critical to the event outcome.

“Even when such pieces (e.g. breakaways, hill climbs, surges, sprint finishes) make a small contribution to overall energy costs, they are critical to the event outcome.”

May combine two claims.

In Shaw et al. (2019), above 70% V̇O2peak, K-LCHF demonstrated reduced economy, with oxygen uptakes higher than expected based on stoichiometry calculations.

“However, above 70% V˙O2peak, K‐LCHF demonstrated reduced economy, with oxygen uptakes being even higher than expected based on stoichiometry calculations.”

• cites Shaw et al. 2019Not checked yet

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In McSwiney et al. (2018), K-LCHF significantly increased peak but not mean power in a 6 s sprint at the start of the time trial and a 3 min critical power test at the end.

“However, K‐LCHF significant increased peak but not mean power (expressed as W kg−1 BM) in a 6 s sprint at the start of the TT and a 3 min critical power test at the end, designed to stimulate the finish of a race when glycogen depleted (McSwiney et al. 2018).”

• cites McSwiney et al. 2018Not checked yet

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In Prins et al. (2019), a free-living K-LCHF diet achieved sustained levels of ketosis, fasting β-HB approximately 0.5 mmol l−1, and increases in maximal rates of fat oxidation from 0.66 to 1.26 g min−1.

“A free‐living version of a K‐LCHF diet achieved sustained levels of ketosis (fasting [β‐HB]: ∼0.5 mmol l−1) and increases in maximal rates of fat oxidation (from 0.66 to 1.26 g min−1).”

• cites Prins et al. 2019Not checked yet

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May combine two claims.

In Shaw et al. (2019), RER-based predictions accounted for only 14% of the increased oxygen uptake at 13.5 km h−1, approximately 77% V̇O2peak, and 55% of the increase seen during the first 2 h of the treadmill run.

“Specifically, RER‐based predictions accounted for only 14% of the increased oxygen uptake at 13.5 km h−1 (∼77% V˙O2peak), and 55% of the increase seen during the first 2 h of the treadmill run (Shaw et al. 2019).”

• cites Shaw et al. 2019Not checked yet

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May combine two claims.

During moderate intensity exercise there may be adequate reserve for a greater, perhaps imperceptible, increase in oxygen demand, but this may be uncompensable at higher intensities.

“Although there may be adequate reserve for a greater, and perhaps imperceptible increase in, oxygen demand during moderate intensity exercise, this may be uncompensable at higher intensities.”

May combine two claims.

CHO metabolism produces a greater ratio of NADH to FADH2 than beta-oxidation, achieving a greater ATP yield per unit oxygen consumption via oxidative phosphorylation.

“CHO metabolism produces a greater ratio of the reducing equivalent NADH (3 coupling sites in the electron transport chain) to FADH2 (2 coupling sides) than ß‐oxidation, thus achieving a greater ATP yield per unit of oxygen consumption via oxidative phosphorylation in the electron transport chain (Leverve et al. 2007).”

• cites Leverve et al. 2007Not checked yet

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May combine two claims.

In Prins et al. (2019), the first time trial at 4 day adaptation was slower than the corresponding HCHO trial, but further trials after 14, 28 and 42 days and a test of V̇O2peak failed to find significant differences compared to HCHO.

“Although the first TT (4 day adaptation) was slower than the corresponding HCHO trial, further trials undertaken after 14, 28 and 42 days, and a test of V˙O2peak, failed to find significant differences in comparison to the HCHO treatment (Prins et al. 2019).”

• cites Prins et al. 2019Not checked yet

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In Prins et al. (2019), mean oxygen uptake during the time trial decreased over the course of HCHO treatment with the reverse occurring during K-LCHF treatment, confirming a difference in exercise economy due to substrate choice.

“However, mean oxygen uptake during the TT decreased over the course of the HCHO treatment with the reverse occurring during the K‐LCHF treatment; this confirms the difference in exercise economy due to substrate choice.”

• cites Prins et al. 2019Not checked yet

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In McSwiney et al. (2018), both K-LCHF and habitual high CHO treatment groups achieved improvements in aerobic fitness without a significant change in total 100 km time.

“Both K‐LCHF and habitual ‘high’ CHO treatment groups achieved improvements in aerobic fitness without a significant change in total 100 km time (Table 2).”

• cites McSwiney et al. 2018Not checked yet

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Adaptation to a non-ketogenic LCHF diet maintained cycling intensities representing 80-85% of peak workload but impaired workloads above 90% W peak.

“Indeed, adaptation to a non‐ketogenic LCHF diet was able to maintain cycling intensities representing 80–85% of peak workload, but impaired workloads above 90% W peak (Peak Power Output). (Havemann et al. 2006).”

• cites Havemann et al. 2006Not checked yet

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In Shaw 2019, those with impaired endurance showed an RER <1.0 and an increase in plasma lactate concentrations, interpreted as reduced capacity for an oxidative fate of muscle glycogen stores.

“Meanwhile, those with impaired endurance showed an RER <1.0 and an increase in plasma lactate concentrations, interpreted as reduced capacity for an oxidative fate of muscle glycogen stores.”

• cites Shaw et al. 2019Not checked yet

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Probably not a substantial claim: may not pass S3 (load-bearing).

Potential explanations for higher reductions in economy include uncoupling of mitochondrial respiration specifically associated with high fat exposure.

“Potential explanations for these higher reductions in economy include observations, from a previous study of a 5 day non‐ketogenic LCHF, of an uncoupling of mitochondrial respiration specifically associated with high fat exposure (Leckey et al. 2018).”

• cites Leckey et al. 2018Not checked yet

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May combine two claims.

In Shaw et al. (2019), there was a doubling of 90% confidence interval ranges with K-LCHF, in contrast to a reduction in variability in the post-treatment HCHO condition.

“However, in contrast to a reduction in the variability of results in the post‐treatment HCHO condition, there was a doubling of 90% confidence interval ranges with K‐LCHF.”

• cites Shaw et al. 2019Not checked yet

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Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based).

These symptoms presumably reflect the lack of CHO substrate to the muscle and brain prior to enhancement of muscle fat utilisation and establishment of sustained ketone support for the central nervous system.

“These symptoms presumably reflect the lack of CHO substrate to the muscle and brain prior to enhancement of muscle fat utilisation and the establishment of sustained ketone support for the central nervous system (CNS).”

May combine two claims.

In McSwiney et al. (2018), the K-LCHF group had significantly higher body fat levels at commencement and recorded a loss of approximately 4 kg body fat, a significant confounding effect on performance, especially for power reported relative to body mass.

“Second, the K‐LCHF group had significantly higher body fat levels at the commencement of the treatment, and recorded a loss of ∼4 kg of body fat; a significant confounding effect on performance, especially for power reported relative to BM.”

• cites McSwiney et al. 2018Not checked yet

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Ketone bodies provide a substrate for peripheral tissues, including heart, CNS and skeletal muscle, but their contribution as an exercise substrate is modified by factors including the protocol used to achieve ketonaemia, training status, acute nutritional status and exercise characteristics.

“Ketone bodies provide a substrate for peripheral tissues, including heart, CNS and skeletal muscle but their contribution as an exercise substrate is modified by factors including the protocol used to achieve ketonaemia (ketogenic diet, prolonged starvation/fasting, exogenous intake), training status, acute nutritional status and exercise characteristics (Evans et al. 2017; Pinckaers et al. 2017).”

• cites Evans et al. 2017Not checked yet

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• cites Pinckaers et al. 2017Not checked yet

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Consistent findings of individual responsiveness and difficulties with subject compliance in free-living studies suggest that problems may persist for some athletes.

“although the consistent findings of individual responsiveness and difficulties with subject compliance in free‐living studies suggests that problems may persist for some athletes.”

May combine two claims.

McSwiney et al. (2018) reported that subjects suffered fatigue and performance impairment for the first 7-10 days of adaptation to the K-LCHF diet, with a performance lag persisting for 4-6 weeks.

“McSwiney & colleagues (2018) reported that subjects suffered fatigue and performance impairment for the first 7–10 days of adaptation to the K‐LCHF diet, with a performance ‘lag’ persisting for 4–6 weeks.”

• cites McSwiney et al. 2018Not checked yet

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In McSwiney et al. (2018), the diet reported by the HCHO group failed to meet guidelines for a 2.5 h endurance event and may have led to sub-optimal performance in the time trial.

“Finally, the diet reported by the HCHO group failed to meet guidelines for a 2.5 h endurance event (Table 1) and may have led to sub‐optimal performance in the TT.”

• cites McSwiney et al. 2018Not checked yet

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Probably not a substantial claim: may not pass S3 (load-bearing).

Caveats apply to the data provided in some of the studies summarised in Table 2.

“Therefore, caveats apply to the data provided in some of the studies summarised in Table 2.”

Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

Rates reported in other studies have been slightly lower, 1.2-1.3 g min−1, perhaps reflecting lower training status/calibre or less strict dietary control under free-living circumstances.

“rates reported in other studies have been slightly lower (1.2–1.3 g min−1), perhaps reflecting lower training status/calibre or less strict dietary control under free‐living circumstances (Prins et al. 2019; Shaw et al. 2019).”

• cites Prins et al. 2019Not checked yet

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• cites Shaw et al. 2019Not checked yet

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Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based).

Increased blood β-HB concentrations occur quickly, reaching 0.8-2.0 mmol l−1 within 2-4 days of the K-LCHF diet.

“Increased blood β‐HB concentrations occur quickly, reaching 0.8–2.0 mmol l−1 within 2–4 days of the K‐LCHF diet.”

Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based).

Benefits might also be seen when the K-LCHF diet supports loss of body fat in athletes who are overweight.

“Benefits might also be seen when the K‐LCHF diet supports loss of body fat in athletes who are overweight.”

May combine two claims.

In McSwiney et al. (2018), the results represent nine athletes who completed the K-LCHF diet and testing protocol; a further seven subjects failed to comply with the diet or complete post-treatment testing.

“First, the results represent nine athletes who completed the K‐LCHF diet and testing protocol; that a further seven subjects failed to comply with the diet or complete the post‐treatment testing reinforces the individual variability in response.”

• cites McSwiney et al. 2018Not checked yet

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May combine two claims.

Cyclists habituated to a K-LCHF diet, approximately 50 g day−1 or 7% energy CHO and 72% fat, sustained mean fat oxidation of 1.2 g min−1 during 2 h cycling at approximately 70% V̇O2peak while the comparison group following higher CHO diets achieved a gradual drift to 0.5 g min−1.

“Cyclists habituated to a K‐LCHF diet (∼50 g day−1 or 7% energy CHO; ∼72% fat) sustained mean fat oxidation of 1.2 g min−1 during 2 h cycling at ∼70% V˙O2peak while the comparison group following higher CHO diets achieved a gradual drift to 0.5 g min−1 (Webster et al. 2016)”

• cites Webster et al. 2016Not checked yet

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A graded protocol in elite ultra-distance athletes showed a Fatmax of 1.54 ± 0.18 g min−1 at approximately 70% V̇O2peak in the K-LCHF group, approximately 82 g day−1 or 10% CHO and 70% fat, compared to 0.67 ± 0.14 g min−1 at approximately 55% V̇O2peak in the control group.

“Meanwhile a graded protocol involving short (2 min) exercise periods in elite ultra‐distance athletes, showed a Fatmax of 1.54 ± 0.18 g min−1 at ∼70% V˙O2peak) in the K‐LCHF group (∼82 g day−1 or 10% CHO, ∼70% fat), compared to 0.67 ± 0.14 g min−1 at ∼55% V˙O2peak in the control group (Volek et al. 2016).”

• cites Volek et al. 2016Not checked yet

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Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based). May combine two claims.

Analysis of an Ironman triathlon noted that elite athletes work at higher absolute rates of energy expenditure and a higher proportion of their individual energy expenditure ceiling than their slower counterparts.

“For example, analysis of an Ironman triathlon noted that elite athletes work at higher absolute rates of energy expenditure and a higher proportion of their individual energy expenditure ceiling than their slower counterparts.”

Probably not a substantial claim: may not pass S1 (asserted), S3 (load-bearing), S4 (based).

This may simply reflect the increased oxygen cost and relative intensity of exercise required for fat oxidation to support the same power production, rather than ongoing impairment of exercise tolerance.

“Although this may simply reflect the increased oxygen cost and relative intensity of exercise required for fat oxidation to support the same power production, rather than ongoing impairment of exercise tolerance”

May combine two claims.

Modelling of characteristics of top finishers suggests that enhanced fat oxidation typical of keto-adaptation would fail to support the requirements of 8 h finish times, but might be sufficient for the energy needs of slower competitors with times >12 h.

“Modelling of the characteristics of top finishers (e.g. speeds, power outputs and exercise economy of running, cycling and swimming) suggests that enhanced fat oxidation typical of keto‐adaptation would fail to support the requirements of 8 h finish times, but might be sufficient for the energy needs of slower competitors with times >12 h (Maunders et al. 2018).”

• cites Maunders et al. 2018Not checked yet

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May combine two claims.

All studies, including the authors' own, use conventional stoichiometric equations that fail to include the contribution of ketone oxidation to substrate use in K-LCHF trials, representing a small but potentially systematic error in calculations of fat and CHO oxidation from gas exchange.

“First, all use conventional stoichiometric equations that fail to include the contribution of ketone oxidation to substrate use in the K‐LCHF trials. This represents a small (but potentially systematic) error in the calculations of fat and CHO oxidation from gas exchange information (Frayn, 1983).”

• cites Frayn, 1983Not checked yet

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• AssumptionThe authors state this as an assumption: V̇O2 and V̇CO2 accurately reflect tissue O2 consumption and CO2 production.
• AssumptionThe authors state this as an assumption: Indirect calorimetry is valid for quantifying substrate oxidation in well-trained subjects during exercise up to approximately 85% V̇O2peak.

May combine two claims.

These findings support earlier suggestions that the K-LCHF diet may be unsuited to events in which higher intensity exercise is critical for success but may have utility in specific scenarios such as moderate-intensity exercise that can be supported by fat oxidation, especially in the presence of an inability or unwillingness to use strategies to maintain high CHO availability.

“These findings support earlier suggestions that the K‐LCHF diet may unsuited to events in which higher intensity exercise is critical for success but may have utility in specific scenarios such as moderate‐intensity exercise that can be supported by fat oxidation, especially in the presence of an inability or unwillingness to use strategies to maintain high CHO availability (Burke, 2015).”

• cites Burke, 2015Not checked yet

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May combine two claims.

Longer periods of 6-12 weeks of K-LCHF diet exposure do not change these observations, suggesting that maximal enhancement of muscle fat oxidation occurs within 3-4 weeks of keto-adaptation.

“Longer periods (6–12 weeks) of K‐LCHF diet exposure do not change these observations (McSwiney et al. 2018; Prins et al. 2019), suggesting that maximal enhancement of muscle fat oxidation occurs within 3–4 weeks of keto‐adaptation.”

• cites McSwiney et al. 2018Not checked yet

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• cites Prins et al. 2019Not checked yet

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Probably not a substantial claim: may not pass S3 (load-bearing).

Lay literature notes that keto flu symptoms may reflect extensive electrolyte and fluid shifts resulting from the initial renal response to the ketogenic diet.

“Lay literature also notes that ‘keto flu’ symptoms may reflect extensive electrolyte and fluid shifts resulting from the initial renal response to the ketogenic diet (Volek & Phinney, 2011).”

• cites Volek & Phinney, 2011Not checked yet

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May combine two claims.

The earliest studies of 3-4 days of CHO-restriction reported glycogen depletion and a lack of metabolic adaptation, and an impairment of endurance capacity/performance.

“The earliest studies of 3–4 days of CHO‐restriction (Ahlborg et al. 1967; Bergstrom et al. 1967) reported glycogen depletion and a lack of metabolic adaptation, and in agreement with Prins et al. (2019), an impairment of endurance capacity/performance.”

• cites Ahlborg et al. 1967Not checked yet

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• cites Bergstrom et al. 1967Not checked yet

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• cites Prins et al. 2019Not checked yet

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May combine two claims.

Reductions in well-being, such as fatigue, irritability and loss of concentration, and increases in perception of effort during exercise are clearly evident in the first few days of exposure to a K-LCHF diet.

“Reductions in well‐being (e.g. fatigue, irritability, loss of concentration) and increases in perception of effort during exercise are clearly evident in the first few days of exposure to a K‐LCHF diet.”

May combine two claims.

Previous studies involving NK-LCHF diets have reported increases in intramuscular triglyceride, hormone sensitive lipase, and expression of fatty acid translocase FAT/CD36 protein and carnitine palmitoyl transferase.

“However, previous studies involving NK‐LCHF diets have reported increases in intramuscular triglyceride (Yeo et al. 2008b ), hormone sensitive lipase (Stellingwerff et al. 2006), and the expression of fatty acid translocase FAT/CD36 protein (Cameron‐Smith et al. 2003) and carnitine palmitoyl transferase (Goedecke et al. 1999).”

• cites Yeo et al. 2008bNot checked yet

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• cites Stellingwerff et al. 2006Not checked yet

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• cites Cameron‐Smith et al. 2003Not checked yet

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May combine two claims.

Performance impairment of higher-intensity exercise is likely, and potentially attributable to reduced exercise economy (higher oxygen cost) that prevents the athlete from sustaining workloads at high proportions of their maximal aerobic capacity.

“Performance impairment of higher‐intensity exercise is likely, and potentially attributable to reduced exercise economy (higher oxygen cost) that prevents the athlete from sustaining workloads at high proportions of their maximal aerobic capacity.”

May combine two claims.

Overall, the studies suggest that performance of moderate-intensity exercise may be preserved following keto-adaptation, but individual results may be extreme in both directions and include inability to tolerate or comply with the dietary restrictions.

“Overall, they suggest that the performance of moderate‐intensity exercise may be preserved following keto‐adaptation, but individual results may be extreme in in both directions and include inability to tolerate or comply with the dietary restrictions.”

Classified as probably not a substantial claim.

It was proposed that prolonged keto-adaptation restores the muscle's ability to synthesise glycogen, which then has a non-oxidative fate during exercise as a source of intermediates for the citric acid cycle and gluconeogenesis in the liver.

“It was proposed that prolonged keto‐adaptation restores the muscle's ability to synthesise glycogen, which then has a non‐oxidative fate during exercise as a source of intermediates for the citric acid cycle and gluconeogenesis in the liver (Volek et al. 2016).”

• cites Volek et al. 2016Not checked yet

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May combine two claims.

Adaptation to endogenous ketone sources requires 5+ days, whereas exogenous ketone supplements involve hours.

“although adaptation to endogenous ketone sources requires 5+ days rather than hours involved with exogenous ketone supplements (Evans et al. 2017).”

• cites Evans et al. 2017Not checked yet

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Probably not a substantial claim: may not pass S1 (asserted), S3 (load-bearing).

Webster et al. (2016) hypothesised that the endogenous glucose production decrease represented reduced liver glycogen breakdown without compensation by an absolute increase in gluconeogenesis.

“They hypothesised that the EGP decrease represented reduced liver glycogen breakdown without compensation by an absolute increase in gluconeogenesis.”

• cites Webster et al. 2016Not checked yet

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Classified as probably not a substantial claim. May combine two claims.

In Volek et al. (2016), ten chronically keto-adapted high performance ultra-runners/triathletes undertook a 3 h run at 65% V̇O2peak after consuming a high-fat snack, then recovered for 2 h following repeated intake of this snack.

“Ten chronically keto‐adapted high performance ultra‐runners/triathletes undertook a 3 h run at 65% V˙O2peak after consuming a high‐fat snack (31 g fat, 80% E), then recovered for 2 h following repeated intake of this snack (Volek et al. 2016).”

• cites Volek et al. 2016Not checked yet

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May combine two claims.

Reduced availability of CHO substrate is an obvious explanation for decreased CHO oxidation, although impaired ability to oxidise available glycogen stores is also evident.

“Reduced availability of CHO substrate is an obvious explanation for this finding, although as discussed in the section below, impaired ability to oxidise available glycogen stores is also evident.”

May combine two claims.

Blood glucose concentrations are maintained at rest and during exercise, albeit at reduced levels, and increases in blood lactate concentrations during aerobic capacity tests are apparent.

“For example, blood glucose concentrations are maintained at rest and during exercise, albeit at reduced levels, and increases in blood lactate concentrations during aerobic capacity tests are apparent (Phinney et al. 1983; Burke et al. 2017; Shaw et al. 2019).”

• cites Phinney et al. 1983Not checked yet

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• cites Burke et al. 2017Not checked yet

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• cites Shaw et al. 2019Not checked yet

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May combine two claims.

In Volek et al. (2016), high rates of fat oxidation, approximately 1.2 g min−1, and low rates of CHO oxidation, less than 0.5 g min−1, were seen in the K-LCHF group, while CHO oxidation in the HCHO group declined from approximately 1.7 to 1.2 g min−1 over the water-fed session.

“High rates of fat oxidation (∼1.2 g min−1) and low rates of CHO oxidation (<0.5 g min−1) were seen in the K‐LCHF group, while CHO oxidation in the HCHO group declined from ∼1.7 to ∼1.2 g min−1 over the course of the water‐fed session (see Fig. 3 A).”

• cites Volek et al. 2016Not checked yet

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May combine two claims.

These two studies show a harmonised understanding of medium- and long-term adaptation of CHO metabolism to K-LCHF diets, both across the time course of changes and the various direct and indirect methodologies of assessing substrate use.

“These two studies show a harmonised understanding of medium‐ and long‐term adaptation of CHO metabolism to K‐LCHF diets, both across the time course of changes and the various direct (biopsy and tracer‐enabled) and indirect (estimates from respiratory gas data) methodologies of assessing substrate use.”

May combine two claims.

In Volek et al. (2016), biopsy-derived data showed equal pre- and post-exercise glycogen storage despite large differences in CHO intake, and equal glycogen degradation during exercise with a non-oxidative fate for the K-LCHF group.

“However, biopsy‐derived data showed a number of inconsistencies (Fig. 3 B): equal pre‐ and post‐exercise glycogen storage despite large differences in CHO intake, and equal glycogen degradation during exercise with a non‐oxidative fate for the K‐LCHF group.”

• cites Volek et al. 2016Not checked yet

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May combine two claims.

This approximates to absolute rates of fat oxidation of approximately 1.3-1.5 g min−1, representing a doubling of this substrate use under the same conditions in a cross-over HCHO treatment.

“This approximates to absolute rates of fat oxidation of ∼1.3–1.5 g min−1, representing a doubling of this substrate use under the same conditions in a cross‐over HCHO treatment.”

May combine two claims.

The data from Volek et al. (2016) on long-term K-LCHF adaptation are atypical and should not be used as a basis for new operating beliefs about long-term adaptation to K-LCHF diets.

“While the concept proposed by Volek & colleagues (2016) is intriguing and merits further systematic evaluation, for the moment, there are strong reasons to reject the data on which it rests as atypical, rather than a basis for new operating beliefs about long‐term adaptation to K‐LCHF diets.”

• cites Volek et al. 2016Not checked yet

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May combine two claims.

The time course of adaptation to achieve high rates of fat oxidation in well-trained athletes seems rapid, 5-10 days, and robust, with similar outcomes achieved by both ketogenic and non-ketogenic versions of the LCHF diet.

“Therefore, the time course of adaptation to achieve high rates of fat oxidation in well‐trained athletes seems rapid (5–10 days) and robust, with similar outcomes achieved by both ketogenic and non‐ketogenic versions of the LCHF diet.”

May combine two claims.

Because of the importance of glucose as a substrate for many tissues and a source of carbon for biosynthesis and anaplerosis, humans can adapt to CHO deprivation by synthesising glucose from a variety of substrates.

“Because of the importance of glucose as a substrate for many tissues and a source of carbon for biosynthesis and anaplerosis, this confirms that humans can adapt to CHO deprivation by synthesising glucose from a variety of substrates (Soeters et al. 2012).”

• cites Soeters et al. 2012Not checked yet

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May combine two claims.

Although absolute rates of gluconeogenesis were similar between groups, they contributed a greater proportion of body CHO stores in the K-LCHF group and came from different substrates; glycerol in the K-LCHF group, and lactate in the HCHO group.

“Although absolute rates of gluconeogenesis were similar between groups, they contributed a greater proportion of body CHO stores in the K‐LCHF group and came from different substrates; glycerol, in the case of the K‐LCHF group, and lactate in the case of the HCHO group (Webster et al. (2016).”

• cites Webster et al. 2016Not checked yet

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May combine two claims.

In cyclists adapted to NK-LCHF with restored CHO availability, 1 km sprints at >90% of peak power output (∼95% of V ̇O2peak) within the TT caused a significant decrease in power output despite maintained perceived effort and heart rate, and an increased attempt to recruit muscle fibres.

“However, when required to undertake 1 km sprints at >90% of peak power output (∼95% of V˙O2peak) within the TT, there was a significant decrease in power output despite the maintenance of perceived effort and heart rate, and an increased attempt to recruit muscle fibres (Havemann et al. 2006).”

• cites Havemann et al. 2006Not checked yet

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Probably not a substantial claim: may not pass S3 (load-bearing).

The case study does not include comparisons to chronically high CHO availability.

“Although this case study encourages further exploration of this and other models of K‐LCHF/HCHO periodisation (e.g. acute glycogen restoration), it does not include comparisons to chronically high CHO availability.”

May combine two claims.

The NK-LCHF diet retooled the muscle to increase fat oxidation but pre-exercise restoration of glycogen stores was thwarted by impaired oxidative CHO disposal due to a decrease in glycogenolysis and a reduction in the active form of pyruvate dehydrogenase (PDHa).

“The NK‐LCHF diet retooled the muscle to increase fat oxidation but pre‐exercise restoration of glycogen stores was thwarted by impaired oxidative CHO disposal due to a decrease in glycogenolysis and a reduction in the active form of pyruvate dehydrogenase (PDHa) (Stellingwerff et al. 2006).”

• cites Stellingwerff et al. 2006Not checked yet

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Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based). May combine two claims.

Various models integrating K-LCHF and HCHO approaches to training and performance support are possible and are practiced in real-life according to testimonials of successful and recreational athletes.

“In summary, various models integrating K‐LCHF and HCHO approaches to training and performance support are possible and are practiced in real‐life according to testimonials of successful and recreational athletes.”

Classified as probably not a substantial claim.

The design of the case study cannot isolate muscle or CNS benefits of CHO intake during exercise.

“The authors concede that their design cannot isolate muscle or CNS (Burke & Maughan, 2020) benefits of CHO intake during exercise.”

• cites Burke & Maughan, 2020Not checked yet

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Probably not a substantial claim: may not pass S4 (based).

There is robust evidence that adaptation to a ketogenic LCHF creates substantial cellular changes to increase the mobilisation, transport, uptake and oxidation of fat during exercise, even in elite athletes who specifically train to optimise fat oxidative pathways.

“There is robust evidence that adaptation to a ketogenic LCHF creates substantial cellular changes to increase the mobilisation, transport, uptake and oxidation of fat during exercise, even in elite athletes who specifically train to optimise fat oxidative pathways.”