Adaptation to a low carbohydrate high fat diet is rapid but impairs endurance exercise metabolism and performance despite enhanced glycogen availability

May combine two claims.

Performance changes from Baseline to Adaptation 10,000 m race differed between high-carbohydrate and low-carbohydrate high-fat groups (P = 0.009), with all high-carbohydrate athletes improving (5.7 (5.6)%) while 6/7 low-carbohydrate high-fat athletes were slower (2.2 (3.4)%).

“Performance changes differed between groups (P = 0.009), with all HCHO athletes improving in the Adaptation race (5.7 (5.6)%), while 6/7 LCHF athletes were slower (2.2 (3.4)%).”

May combine two claims.

After acute carbohydrate restoration in low-carbohydrate high-fat-adapted athletes, fat oxidation during race warm-up remained elevated above baseline but lower than after 5-6 days of keto adaptation; carbohydrate oxidation reached only 61% and 78% of values previously seen at exercise intensities related to race events.

“Fat oxidation continued to be elevated above baseline values although it was lower than achieved by 5–6 days’ keto adaptation; CHO oxidation only reached 61% and 78% of values previously seen at exercise intensities related to race events.”

• AssumptionThe authors state this as an assumption: The equations used to calculate carbohydrate and fat oxidation from V̇CO2 and V̇O2 (non-protein respiratory exchange ratio) accurately reflect tissue O2 consumption and CO2 production, and indirect calorimetry is a valid method for quantifying substrate oxidation in well-trained athletes during strenuous exercise up to ∼85% of V̇O2peak.

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

Assessments of exercise energy expenditure showed a daily mean of approximately 1600 kcal (6720 kJ) for the HCHO group across all phases.

“Assessments of exercise energy expenditure (EEE) showed a daily mean of ∼1600 kcal (6720 kJ) for HCHO group across all phases.”

May combine two claims.

Metabolic changes from low-carbohydrate high-fat adaptation were washed out after 5-6 days of high-carbohydrate diet, with substrate utilisation returning to Baseline values.

“Brief (5–6 days) adaptation to a low carbohydrate high fat diet in elite athletes increased exercise fat oxidation to rates previously observed with medium (3–4 weeks) or chronic (>12 months) adherence to this diet, with metabolic changes being washed out in a similar time frame.”

• Also stated in: § Abstract · plain

  “Substrate utilisation returned to Baseline values after 5–6 days of HCHO diet.”

• AssumptionThe authors state this as an assumption: The equations used to calculate carbohydrate and fat oxidation from V̇CO2 and V̇O2 (non-protein respiratory exchange ratio) accurately reflect tissue O2 consumption and CO2 production, and indirect calorimetry is a valid method for quantifying substrate oxidation in well-trained athletes during strenuous exercise up to ∼85% of V̇O2peak.

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

Overall exercise energy expenditure was not different between groups, but the LCHF group incurred a reduced expenditure during the intervention compared with Baseline (P = 0.008) and Restoration (P = 0.18).

“Overall EEE was not different between groups, but the LCHF group incurred a reduced expenditure during the intervention compared with Baseline (P = 0.008) and Restoration (P = 0.18).”

May combine two claims.

The LCHF group achieved the targets of their dietary prescription, consuming less than 5% of energy and less than 0.5 g kg−1 as CHO and 80% of energy from fat.

“The LCHF group achieved the targets of their dietary prescription, consuming <5% of energy and <0.5 g kg−1 as CHO and 80% of energy from fat.”

May combine two claims.

There were no differences between groups at baseline (P = 0.419) or across the intervention period in absolute V ̇O2peak (HCHO, P = 0.315; LCHF, P = 0.493).

“There were no differences between groups at baseline (P = 0.419) or across the intervention period in absolute V˙O2peak (HCHO, P = 0.315; LCHF, P = 0.493).”

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

During the intervention phase, protein intake was maintained across both groups at the target of approximately 2.2 g kg−1 BM day−1.

“During the intervention phase, protein intake was maintained across both groups at the target of ∼2.2 g kg−1 BM day−1.”

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

There were no significant differences between groups for energy and macronutrient intake characteristics for the Baseline and Restoration phases.

“There were no significant differences between groups for energy and macronutrient intake characteristics for the Baseline and Restoration phases”

May combine two claims.

Each group was able to achieve the main targets for the Baseline and Restoration phases: energy availability of approximately 40 kcal (168 kJ) kg−1 FFM day−1, protein intake of approximately 2 g kg−1 BM day−1, and CHO intake of 9-9.5 g kg−1 BM day−1 contributing approximately 65% of energy.

“each group was able to achieve the main targets for these phases: EA of ∼40 kcal (168 kJ) kg−1 FFM day−1, protein intake of ∼2 g kg−1 BM day−1, and CHO intake of 9–9.5 g kg−1 BM day−1 contributing ∼65% of energy.”

May combine two claims.

Within the HCHO group, there were no differences between Walks 1-3 in relative V ̇O2 (P = 0.113) or CHO oxidation (P = 0.258).

“Within the HCHO group, there were no differences between Walks 1–3 in relative V˙O2 (Fig. 4A , P = 0.113) or CHO oxidation (Fig. 4B , P = 0.258)”

May combine two claims.

There was a robust increase in circulating blood β-hydroxybutyrate in Walk 2 in the LCHF group (P = 0.0004 vs. Walk 1 and Walk 3), peaking at 1.7 (0.9) mmol L−1 towards the end of the trial, but there were no differences in the HCHO group.

“Similarly, there was a robust increase in circulating blood β‐hydroxybutyrate in the Walk 2 in the LCHF group (P = 0.0004 vs. Walk 1 and Walk 3), peaking at 1.7 (0.9) mmol L−1 towards the end of the trial, but there were no differences in the HCHO group.”

May combine two claims.

Athletes raced competitively, with finishing times for the post-intervention races representing 103 (3)% and 104 (8)% of the lifetime personal best times of walkers in the HCHO and LCHF groups, respectively, and four athletes recording times faster than their personal bests.

“Athletes raced competitively, with finishing times for the post‐intervention races representing 103 (3)% and 104 (8)% of the life‐time personal best times of walkers in the HCHO and LCHF groups, respectively, and four athletes recording times faster than their personal bests”

May combine two claims.

Despite the lack of a statistically significant (P = 0.222) change in maximum aerobic capacity (relative V ̇O2peak), all six athletes in the HCHO group improved performance by an average of 5.7 (5.6)%.

“Despite the lack of a statistically significant (P = 0.222) change in maximum aerobic capacity (relative V˙O2peak, Fig. 7A ), all six athletes in the HCHO group improved performance by an average of 5.7 (5.6)%.”

• AssumptionRests on an assumption: Differences in environmental conditions between the Baseline and Adaptation 10,000 m races did not materially affect race performance.

May combine two claims.

LCHF adaptation increased fat oxidation rates across all four stages (P < 0.0001), peaking at 1.43 g min−1 in the first stage (11-12 km h−1).

“fat oxidation rates increased across all four stages (P < 0.0001), peaking at 1.43 g min−1 in the first stage (11–12 km h−1)”

May combine two claims.

Blood lactate concentrations increased with exercise intensity across both dietary treatments (P < 0.0001), with similar patterns in both pre- and post-treatment trials for the HCHO group.

“Blood lactate concentrations increased with exercise intensity across both dietary treatments (P < 0.0001), with similar patterns in both pre‐ and post‐treatment trials for the HCHO group”

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

HCHO group body mass decreased by an average of 0.96 (0.44) kg over each of the three approximately 2 h training walks (P < 0.0001).

“while BM decreased by an average of 0.96 (0.44) kg over each of the three ∼2 h training walks (P < 0.0001).”

May combine two claims.

For the HCHO group, RPE (P < 0.0001) and HR (P < 0.0001) increased across the test, but this was not different between Walks 1-3 (P = 0.906).

“Similarly, RPE (P < 0.0001) and HR (P < 0.0001) increased across the test for the HCHO group, but this was not different between Walks 1–3 (P = 0.906).”

May combine two claims.

In the HCHO diet, no effect of diet was detected on relative V ̇O2 (P = 0.812) or fat oxidation rates (P = 0.139).

“no effect of diet was detected on relative V˙O2 (ml min−1 kg−1, P = 0.812) or fat oxidation rates (P = 0.139).”

May combine two claims.

There was a main effect of stage on blood glucose concentrations, reflecting exercise intensity, but this was unaltered by adaptation to diet in either the HCHO (P = 0.694) or LCHF (P = 0.308) group.

“There was a main effect of stage on blood glucose concentrations, reflecting exercise intensity, but this was unaltered by adaptation to diet in either the HCHO (P = 0.694) or LCHF (P = 0.308) group”

May combine two claims.

There were no differences in blood glucose concentrations across testing blocks (Walks 1-3) in the HCHO group (P = 0.355), but there was a main effect for distance as blood glucose increased across the 25 km trial (P = 0.0009).

“There were no differences in blood glucose concentrations across testing blocks (Walks 1–3) in the HCHO group (P = 0.355), but there was a main effect for distance as blood glucose increased across the 25 km trial consistent with the continuous intake of CHO (P = 0.0009).”

May combine two claims.

There were no differences in relative V ̇O2 (P = 0.999) or substrate utilisation (P < 0.999, P = 0.850) between Walk 1 and Walk 3 in the LCHF group.

“there were no differences in relative V˙O2 (Fig. 4D , P = 0.999) or substrate utilisation (Fig. 4E , P < 0.999, Fig. 4F , P = 0.850) between Walk 1 and Walk 3”

May combine two claims.

Blood ketone levels in the HCHO group were maintained at low concentrations (0.0-0.1 mmol L−1), with no differences across the economy test for both pre- and post-treatment.

“Blood ketone levels in the HCHO group were maintained at low concentrations (0.0–0.1 mmol L−1), with no differences across the economy test for both pre‐ and post‐treatment.”

May combine two claims.

Within the HCHO group, a main effect for testing block was detected for fat oxidation (P = 0.003), with Walk 2 displaying higher overall rates compared to Walk 1 (P = 0.03) and Walk 3 (P = 0.003).

“however, a main effect for testing block was detected for fat oxidation (Fig. 4C , P = 0.003), with Walk 2 (Adaptation) displaying higher overall rates compared to Walk 1 (Baseline, P = 0.03) and 3 (Restoration, P = 0.003).”

May combine two claims.

There was a significant interaction between diet and time for race results (P = 0.02), and a significant difference between performance changes between the two groups (P = 0.009).

“There was a significant interaction between diet and time for race results (P = 0.02), and a significant difference between performance changes between the two groups (P = 0.009).”

• Also stated in: § 10,000 m race · plain

  “The difference between changes in performance from Race 1 to Race 2 was significant (P = 0.009) (Fig. 7C ).”

• AssumptionRests on an assumption: Differences in environmental conditions between the Baseline and Adaptation 10,000 m races did not materially affect race performance.

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

The LCHF group had no significant change in post-exercise body mass following Walk 2 (0.28 (0.45) kg, P = 0.110).

“but there was no significant change in post‐exercise body mass following Walk 2 (0.28 (0.45) kg, P = 0.110).”

May combine two claims.

Both groups had a significant increase in both absolute and relative V ̇O2 over the 25 km walks.

“which was associated with a significant increase in both absolute and relative V˙O2 (Table 4 and Fig. 4A and D ), respectively)”

May combine two claims.

LCHF adaptation increased RPE at Stages 1-3 (P < 0.0001) but not Stage 4 (P = 0.149).

“RPE (Stages 1–3 higher, P < 0.0001; Stage 4, P = 0.149)”

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

The LCHF group had body mass decreases in Walk 1 (0.92 (0.72) kg, P < 0.0001) and Walk 3 (0.69 (0.39) kg, P = 0.0002).

“The LCHF group followed a similar trend for BM changes in Walk 1 (0.92 (0.72) kg, P < 0.0001) and Walk 3 (0.69 (0.39) kg, P = 0.0002)”

May combine two claims.

Both groups displayed an increase in RER, absolute V ̇O2, HR and RPE associated with the increase in exercise intensity across all four stages of both economy tests (all P < 0.0001).

“Both groups displayed an increase in RER, absolute V˙O2 (L min−1), HR and RPE associated with the increase in exercise intensity across all four stages of both economy tests (all P < 0.0001).”

May combine two claims.

In the LCHF group, HR (P < 0.0001) and RPE (P = 0.0005) increased across the session for all three walks, and this was more pronounced in the Adaptation test block.

“While HR (P < 0.0001) and RPE (P = 0.0005) increased across the session for all three walks in the LCHF group, this was more pronounced in the Adaptation test block (Table 4).”

May combine two claims.

The LCHF group displayed substantially altered fuel utilisation in Walk 2, with fat oxidation being significantly increased in comparison to Walks 1 and 3 (P < 0.0001), and a reciprocal decrease in CHO oxidation (P < 0.0001).

“the LCHF group displayed substantially altered fuel utilisation in Walk 2, with fat oxidation being significantly increased in comparison to Walks 1 and 3 (P < 0.0001), and a reciprocal decrease in CHO oxidation (P < 0.0001).”

May combine two claims.

The LCHF group displayed significant increases in blood ketone concentrations following the dietary intervention (P = 0.008), which were highest at rest (1.2 (0.79) mmol L−1).

“the LCHF group displayed significant increases in blood ketone concentrations following the dietary intervention (P = 0.008), which were highest at rest (1.2 (0.79) mmol L−1).”

May combine two claims.

Within the LCHF group, the dietary intervention increased absolute V ̇O2 at Stages 1-4 (P < 0.005) but not V ̇O2peak (P = 0.493).

“Within the LCHF group, there was a significant effect of the dietary intervention (Baseline vs. Adaptation) on metabolic cost and perceived effort, with changes to absolute V˙O2 (L min−1) (Stages 1–4 higher, P < 0.005; V˙O2peak P = 0.493)”

May combine two claims.

The LCHF group displayed a main effect for testing block (P < 0.0001), with blood glucose concentrations increasing in Walk 1 and to a lesser extent in Walk 3 (P = 0.03 vs. Walk 1), but decreasing in Walk 2 (P < 0.0001 vs. Walk 1 and 3).

“In contrast, the LCHF group displayed a main effect for testing block (P < 0.0001), with blood glucose concentrations (Fig. 5A ) increasing in Walk 1 (Baseline) and to a lesser extent in Walk 3 (Restoration, P = 0.03 vs. Walk 1), but decreasing in Walk 2 (Adaptation, P < 0.0001 vs Walk 1 and 3).”

May combine two claims.

In contrast, 6 of 7 LCHF athletes displayed impaired performance with a mean race time that was 2.2 (3.4)% slower, despite a small but significant increase in relative V ̇O2peak (P = 0.025).

“In contrast, 6 of 7 LCHF athletes displayed impaired performance with a mean race time that was 2.2 (3.4)% slower (Fig. 7B ), despite a small but significant increase in relative V˙O2peak (P = 0.025).”

• AssumptionRests on an assumption: Differences in environmental conditions between the Baseline and Adaptation 10,000 m races did not materially affect race performance.

May combine two claims.

Walk 2 undertaken with the LCHF diet was slightly but significantly slower than the other walks (2:11:44 (0:09:26), P = 0.0016 vs. Walk 1, 2:04:14 (0:05:34), P = 0.0005 vs. Walk 3, 2:03:22 (0:04:02); Walk 1 vs. Walk 3, P = 0.953).

“Walk 2 undertaken with the LCHF diet was slightly but significantly slower than the other walks (2:11:44 (0:09:26), P = 0.0016 vs. Walk 1, 2:04:14 (0:05:34), P = 0.0005 vs. Walk 3, 2:03:22 (0:04:02); Walk 1 vs. Walk 3, P = 0.953).”

May combine two claims.

There was a main effect for both distance (P = 0.0046) and test block (P < 0.0001) in blood lactate responses in the LCHF group, as there was a decrease across the trial in Walks 1 and 3, while lactate increased across Walk 2 (P = 0.0007 vs. Walk 1, P < 0.0001 vs. Walk 3).

“There was a main effect observed for both distance (P = 0.0046) and test block (P < 0.0001) in blood lactate responses in the LCHF group (Fig. 5B ), as there was a decrease across the trial in Walks 1 and 3, while lactate increased across Walk 2 (P = 0.0007 vs. Walk 1, P < 0.0001 vs. Walk 3).”

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

In Race 1, there was tight replication of substrate use at the Stage 2 and Stage 4 treadmill speeds.

“In the case of Race 1, we found tight replication of substrate use at the Stage 2 and Stage 4 treadmill speeds which relate to the pace required for the 50 km and 20 km race walking events on the current Olympic program, respectively.”

May combine two claims.

Other metabolic features associated with 3.5 weeks of keto adaptation were also observed after 5-6 days; blood glucose was maintained at lower, albeit euglycaemic, concentrations during exercise while βHB was elevated above 1 mmol L−1 at rest and during exercise.

“Other metabolic features associated with 3.5 weeks of keto adaptation (Burke et al. 2017, 2020) were also observed after 5–6 days; blood glucose was maintained at lower, albeit euglycaemic, concentrations during exercise while βHB was elevated above 1 mmol L−1 at rest and during exercise.”

• cites Burke et al. 2017, 2020Not checked yet

  Not checked in the free run.

May combine two claims.

The current study contributes new knowledge by showing that gross changes in substrate utilisation and metabolism during exercise in response to keto adaptation are reversed by 5 days of reintroduction of a HCHO diet.

“Although our current study does not provide such information, it contributes new knowledge by showing that gross changes in substrate utilisation and metabolism during exercise in response to keto adaptation are reversed by 5 days of reintroduction of a HCHO diet.”

May combine two claims.

The performance changes from Race 1 to Race 2 were significantly different between the HCHO and LCHF groups, with a uniform and significant improvement in race times in the HCHO group and a strong trend to performance impairment in the LCHF group.

“The performance changes from Race 1 to Race 2 in the current study were significantly different and manifested as a uniform and significant improvement in race times in the HCHO group and a strong trend to performance impairment in the LCHF group, with only one participant recording a faster race outcome in Race 2 following the LCHF adaptation/enhanced CHO availability intervention.”

May combine two claims.

During the Race 2 warm-up, acute restoration of CHO availability increased rates of CHO oxidation and reduced the contribution of fat oxidation to energy production compared with the previous day's economy test under full keto adaptation conditions.

“During the Race 2 warm‐up, acute restoration of CHO availability increased rates of CHO oxidation and reduced the contribution of fat oxidation to energy production compared with the previous day's economy test undertaken under full keto adaptation conditions.”

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

The ~8% difference in performance changes between the HCHO and LCHF groups was strikingly similar to previous findings.

“The ∼8% difference in performance changes between the HCHO and LCHF groups was strikingly similar to our previous findings (Burke et al. 2017, 2020), providing additional confidence around these results.”

• cites Burke et al. 2017, 2020Not checked yet

  Not checked in the free run.

Classified as probably not a substantial claim.

Current sports nutrition guidelines state that performance of sustained high-intensity endurance sports is best supported by high carbohydrate availability.

“According to current sports nutrition guidelines, the performance of sustained high‐intensity endurance sports is best supported by conditions of high carbohydrate (CHO) availability (Thomas et al. 2016), defined as matching the finite body CHO stores to event‐specific muscle and central nervous system fuel needs (Burke et al. 2018 a).”

• cites Thomas et al. 2016Not checked yet

  Not checked in the free run.

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

Daily checks of compliance to the training plan, dietary prescription and reporting requirements were undertaken.

“Daily checks of compliance to the training plan, dietary prescription and reporting requirements were undertaken, with food choices and portion sizes being adjusted at meals eaten in the later part of the day if actual training deviated from the plan.”

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

The study conformed to the standards set by the Declaration of Helsinki and was approved by the Human Research Ethics Committee of the Australian Institute of Sport (no. 20181203).

“It conformed to the standards set by the Declaration of Helsinki and was approved by the Human Research Ethics Committee of the Australian Institute of Sport (no. 20181203).”

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

The specific multi-system physiological responses to keto adaptation and the timelines required to achieve them are contentious.

“The specific multi‐system physiological responses to keto adaptation are contentious, as are the timelines required to achieve them (Lindseth, 2017; Burke et al. 2020).”

• cites Lindseth, 2017Not checked yet

  Not checked in the free run.

• cites Burke et al. 2020 sourceNot checked yet

  Not checked in the free run.

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

Competitive endurance athletes do not always achieve high carbohydrate availability goals, for reasons that are either accidental or intentional.

“Yet, competitive endurance athletes do not always achieve these goals, for reasons that are either accidental or intentional (Heikura et al. 2018).”

• cites Heikura et al. 2018Not checked yet

  Not checked in the free run.

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

The study was registered with the Australian New Zealand Clinical Trials Registry (ACTRN12618001974291p).

“This study was registered with the Australian New Zealand Clinical Trials Registry (ACTRN12618001974291p).”

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

In events lasting longer than 90 min, provision of additional carbohydrate substrate from foods or fluids consumed during exercise becomes more important.

“In events lasting longer than 90 min, the provision of additional CHO substrate from foods/fluids consumed during exercise becomes more important (Stellingwerff & Cox, 2014).”

• cites Stellingwerff & Cox, 2014Not checked yet

  Not checked in the free run.

May combine two claims.

The study did not correct calculations for the contribution of ketone oxidation to substrate use, which may cause a small but systematic error in the use of conventional equations to calculate fat and carbohydrate oxidation from gas exchange.

“We did not correct our calculations for the contribution of ketone oxidation to substrate use in order to contextualise our findings with previous work performed by our group (Stellingwerff et al. 2006; Burke et al. 2017) as well as other reports of substrate utilisation in ultra‐endurance athletes who chronically consume LCHF diets (Volek et al. 2016; Webster et al. 2016). However, we acknowledge”

• cites Stellingwerff et al. 2006Not checked yet

  Not checked in the free run.

• cites Burke et al. 2017Not checked yet

  Not checked in the free run.

• cites Volek et al. 2016Not checked yet

  Not checked in the free run.

• AssumptionThe authors state this as an assumption: The equations used to calculate carbohydrate and fat oxidation from V̇CO2 and V̇O2 (non-protein respiratory exchange ratio) accurately reflect tissue O2 consumption and CO2 production, and indirect calorimetry is a valid method for quantifying substrate oxidation in well-trained athletes during strenuous exercise up to ∼85% of V̇O2peak.

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

All foods and fluids consumed during the study were provided and recorded by the research team.

“All foods and fluids consumed during the study were provided and recorded by the research team, with menu construction and food preparation being undertaken by a professional chef, food service dietitians and sports dietitians.”

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

A deliberate contrast to current guidelines is the revived interest in low-carbohydrate high-fat diets, due to observations that athletes can achieve substantial increases to their already enhanced capacity for oxidising fat during exercise, including an increase in the exercise intensity at which maximal rates of fat oxidation occur.

“A deliberate contrast to these guidelines is the revived interest in adaptation to low CHO, high fat (LCHF) diets, due to observations that athletes can achieve substantial increases to their already enhanced capacity for oxidising fat during exercise, including an increase in the exercise intensity at which maximal rates of fat oxidation occur (for review, see Burke, 2021).”

• cites Burke, 2021Not checked yet

  Not checked in the free run.

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

High carbohydrate availability can be achieved via targeted dietary carbohydrate intake over the 24-36 h prior to a race to normalise or super-compensate muscle glycogen concentrations, supplemented by a pre-race carbohydrate-rich meal.

“High CHO availability (HCHO) can be achieved via targeted dietary CHO intake over the 24–36 h prior to the race to normalise or super‐compensate muscle glycogen concentrations (Burke et al. 2011), supplemented by a pre‐race CHO‐rich meal to restore liver glycogen content and provide ongoing release of glucose from the gut within the race (Coyle, 1991).”

• cites Burke et al. 2011Not checked yet

  Not checked in the free run.

• cites Coyle, 1991Not checked yet

  Not checked in the free run.

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

Race walkers were allocated to a preferred dietary condition while achieving suitable matching between groups based on age, body mass, aerobic capacity and personal best for the 20 km race walk.

“We were able to allocate race walkers to a preferred dietary condition while achieving suitable matching between groups based on age, body mass, aerobic capacity and personal best for the 20 km race walk (Table 1).”

May combine two claims.

All athletes demonstrated compliance to their assigned dietary treatment and the monitoring of their food intake and training sessions.

“All athletes demonstrated compliance to their assigned dietary treatment and the monitoring of their food intake and training sessions.”

May combine two claims.

Whereas aerobic reserve can accommodate the trade-off of increased oxygen cost during moderate-intensity exercise, oxygen availability may become a limiting factor for energy production at higher intensities, contributing to a reduction in performance.

“Whereas the aerobic reserve can accommodate this trade‐off during moderate intensity exercise, oxygen availability may become a limiting factor for energy production at higher intensities, contributing to a reduction in performance.”

May combine two claims.

The effects of LCHF adaptation on relative V ̇O2 and substrate utilisation were transient and the restoration period was sufficient to restore metabolic flexibility.

“indicating these effects were transient and the restoration period was sufficient to restore metabolic flexibility.”

May combine two claims.

Muscle retooling to enhance fat oxidation with brief exposure to ketogenic LCHF is maintained in the face of acute increases in muscle CHO availability, but is reversed by 5 days of chronic high CHO diet.

“muscle retooling to enhance fat oxidation with brief exposure to a ketogenic LCHF is maintained in the face of acute increases in muscle CHO availability, but is reversed by 5 days of chronic high CHO diet”

• AssumptionRests on an assumption: A 1-day HCHO diet restores or enhances skeletal muscle glycogen availability after LCHF adaptation.

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

Some studies have reported fat oxidation rates approaching 2 g min−1 in elite athletes with larger body mass and high V ̇O2peak characteristics.

“indeed some studies have reported rates approaching 2 g min−1 in elite athletes with larger BM and high V˙O2peak characteristics (Burke et al. 2017).”

• cites Burke et al. 2017Not checked yet

  Not checked in the free run.

May combine two claims.

The increase in relative oxygen cost of walking in Walk 2 (P = 0.005 vs. Walk 1, P = 0.001 vs. Walk 3) indicates an increase in perceived effort and metabolic cost of exercise when relying on fat as the primary fuel.

“When combined with the significant increase in the relative oxygen cost of walking in Walk 2 (Fig. 4D ; P = 0.005 vs. Walk 1, P = 0.001 vs. Walk 3), this indicates an increase in the perceived effort and metabolic cost of exercise when relying on fat as the primary fuel.”

Classified as probably not a substantial claim.

All athletes performed the three hybrid laboratory-field test 25 km walks.

“All athletes performed the three hybrid laboratory‐field test 25 km walks”

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

Lower maximal fat oxidation rates of 1.1-1.4 g min−1 reported in other studies of ketogenic LCHF diets may reflect low body mass or lower absolute aerobic capacity of the athlete or different exercise protocols, rather than incomplete adaptation.

“the lower maximal fat oxidation rates of 1.1–1.4 g min−1 reported in other studies of ketogenic LCHF diets (Prins et al. 2019; Shaw et al. 2019; Burke et al. 2020) may reflect low BM or lower absolute aerobic capacity of the athlete (including females or individuals of lower calibre) or different exercise protocols, rather than incomplete adaptation.”

• cites Prins et al. 2019Not checked yet

  Not checked in the free run.

• cites Shaw et al. 2019Not checked yet

  Not checked in the free run.

• cites Burke et al. 2020 sourceNot checked yet

  Not checked in the free run.

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

The study had non-random allocation to treatment to enhance placebo effects.

“We acknowledge some potential limitations of the study design; non‐random allocation to treatment to enhance placebo effects, differences between subjects in terms of pre‐race warm up and supplement use (although standardised within subjects for both races), and the possibility that the acute effects on race results were muddied by a chronic effect of the LCHF on training outcomes.”

May combine two claims.

Phinney and co-workers (1983) reported that glycogen utilisation was reduced 4-fold, and blood glucose utilisation 3-fold, during moderate intensity (62-64% VO2peak) cycling after a 4-week ketogenic LCHF diet.

“Phinney and co‐workers (1983) reported that glycogen utilisation was reduced 4‐fold, and blood glucose utilisation, 3‐fold, during moderate intensity (62–64% V˙O2peak) cycling after a 4‐week ketogenic LCHF diet.”

• cites Phinney et al. 1983Not checked yet

  Not checked in the free run.

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

The acute effects on race results may have been muddied by a chronic effect of the LCHF on training outcomes.

“We acknowledge some potential limitations of the study design; non‐random allocation to treatment to enhance placebo effects, differences between subjects in terms of pre‐race warm up and supplement use (although standardised within subjects for both races), and the possibility that the acute effects on race results were muddied by a chronic effect of the LCHF on training outcomes.”

• AssumptionRests on an assumption: The acute effects on race results were not muddied by a chronic effect of the LCHF on training outcomes.

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

The inability to undertake invasive procedures with world-class athletes prevented the taking of muscle biopsies to measure pre-race muscle glycogen stores.

“The inability to undertake invasive procedures with world class athletes prevented us from taking muscle biopsies to measure pre‐race muscle glycogen stores.”

May combine two claims.

De-adaptation probably follows a similar time course to adaptation, with robust modifications in place by 5 days.

“This demonstrates that de‐adaptation probably follow a similar time course to adaptation; although our data cannot inform the processes that occur between 1 and 5 days of each exposure, it seems that robust modifications are in place by this latter time point.”

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

There were differences between subjects in pre-race warm up and supplement use, although these were standardised within subjects for both races.

“We acknowledge some potential limitations of the study design; non‐random allocation to treatment to enhance placebo effects, differences between subjects in terms of pre‐race warm up and supplement use (although standardised within subjects for both races), and the possibility that the acute effects on race results were muddied by a chronic effect of the LCHF on training outcomes.”

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

A case history (Webster et al. 2018) reported a 2.8% improvement in 20 km cycling TT time, no change in 30 s sprint power, a small improvement in 4 min sprint power (1.6%), and a small reduction in 100 km TT time (1.1%) after reintroducing exogenous CHO availability.

“Meanwhile, a case history (Webster et al. 2018) in which a highly successful ultra‐endurance triathlete reintroduced exogenous CHO availability before or during a series of performance tasks reported a 2.8% improvement in 20 km cycling TT time, no change in 30 s sprint power, a small improvement in 4 min sprint power (1.6%), and a small reduction in 100 km TT time (1.1%).”

• cites Webster et al. 2018Not checked yet

  Not checked in the free run.

May combine two claims. The quote only partly states this claim.

In Havemann et al. (2006), well-trained subjects completed a 100 km cycling time trial with crossover application of fat-adaptation, glycogen-restoration strategy or chronic HCHO diet; overall time trial showed a non-significant trend (3 min 43 s) towards faster time in the HCHO trial, and power output during 1 km sprints at ∼90% W peak was significantly reduced with LCHF+HCHO.

“In this study, well‐trained subjects completed a 100 km cycling time trial with a crossover application of the fat‐adaptation, glycogen‐restoration strategy or a chronic HCHO diet. While overall time trial showed a non‐significant trend (3 min 43 s) towards faster time in the HCHO trial, the effects on performance were amplified with higher intensity exercise in the form of sprints integrated”

• cites Havemann et al. 2006Not checked yet

  Not checked in the free run.

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

The mechanism of performance benefits observed in higher intensity exercise in the case history could not be distinguished between alterations in fuel use, effects of enhanced training support, or central nervous system effects of CHO mouth rinsing.

“However, the mechanism of performance benefits observed in the higher intensity exercise could not be distinguished between alterations in fuel use, the effects of enhanced training support, or central nervous system effects of CHO mouth rinsing during the performance trials (Burke & Maughan, 2015).”

• cites Burke & Maughan, 2015Not checked yet

  Not checked in the free run.

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

Exogenous CHO availability appeared to have a small effect on fat utilisation during the 100 km TT but increased rates of CHO oxidation in the case history.

“Exogenous CHO availability appeared to have a small effect on fat utilisation during the 100 km TT but increased rates of CHO oxidation (Webster et al. 2018).”

• cites Webster et al. 2018Not checked yet

  Not checked in the free run.