. 2021 Feb 2;13(2):491. doi: 10.3390/nu13020491

Table 1.

Studies investigating the potential effects of vegetarian, fasting, high-fat, gluten-free, and low-FODMAP diets on athletes’ endurance performance.

Subjects	Study Design	Diet/Application	Duration	Exercise Protocol(s)	Main Findings	Ref.
High-Fat Diets
Endurance-trained male athletes (n = 20)	A non-randomized control trial	K-LCHF diet (n = 9; %CHO:fat:protein = 6:77:17) or HCD (n = 11; 65:20:14)	12 weeks	A 100-km TT performance, a 6-s sprint, and a CPT	↓ Body mass ↓ Body fat percentage ↑ Average relative power during the 6 s sprint sprint and CPT ↑ Fat oxidation during exercise ↔ 100 km TT endurance performance	[14]
Recreational male athletes (n = 14)	A randomized, crossover design	K-LCHF diet (<10%CHO, 75% fat) and 2 week HCD (>50% CHO), >2 weeks washout period in between	2 weeks	A 90-min bicycle ergometer exercise test at 60%Wmax	↓ Exercise-induced cortisol response; however, better results observed in HCD ↓ Exercise capacity ↑ Fat oxidation during exercise ↑ Perceived exertion after exercise ↔ Post-exercise s-IgA levels at week 2	[15]
Professional male race walkers (n = 25)	A mix of repeated-measures and parallel-group design	K-LCHF diet (n = 10; 75–80% FAT, <50 g CHO, 17% protein), HCD (n = 8; 60–65% CHO, 20% FAT, 15–20% protein), or PCD, (n = 7; 60–65% CHO, 20% FAT, 15–20% protein)	3 weeks	- A graded walking economy and VO₂peak test on treadmill - A 10-km race walk (field) - A 25-km standardized race walk	↔ VO₂peak ↓ 10 km race walk performance ↑ Perceived exertion after exercise ↑ Oxygen cost ↑ Fat oxidation during exercise	[16]
Male and female elite race walkers (n = 24)	A mix of repeated-measures and parallel-group design	K-LCHF diet (n = 9; 75–80% FAT, <50 g CHO, 15–20% protein), HCD (n = 8; 60–65% CHO, 20% FAT, 15–20% protein), or PCD, (n = 7; 60–65% CHO, 20% FAT, 15–20% protein)	3 weeks	- A graded walking economy and VO₂peak test on treadmill	↔ VO₂peak ↔ Blood acid-base status	[17]
Endurance-trained male athletes (n = 8)	A randomized repeated-measures crossover study	K-LCHF diet (75–80% FAT, <50 g CHO, 15–20% protein), HCD (43% CHO, 38% FAT, 19% protein)	4.5 weeks	- A graded metabolic test to exhaustion - A TTE performance at 70% VO₂max	↔ TTE performance ↔ Perceived exertion after exercise ↓ Exercise efficiency above 70% VO₂max ↔Exercise efficiency above 70% VO₂max	[18]
Recreationally competitive male runners (n = 8)	A pre–post-test	K-LCHF diet (<50 g CHO, 70% FAT (ad libitum), or HCD (habitual diet defined as moderate to high CHO)	3 weeks	- Five 10-min running bouts at multiple individual race paces in the heat, 20-min rest, then a 5 km TT performance after 50 min of running in challenging environmental conditions	↔ 5 km TT performance ↔ Perceived exertion after exercise ↑ Fat oxidation during exercise ↓ Body mass ↓ Skinfold thickness ↔ Exercise-induced cardiorespiratory, thermoregulatory, or perceptual responses	[19]
Elite male cyclists (n = 5)	A pre–post-test	K-LCHF diet (<20 g CHO, 85% FAT, 15% protein) for 3 weeks immediately after a 1 week HCD (66% CHO, 33%FAT, 1.75 g protein/kg BW/d)	4 weeks (3 weeks LCKD after 1 week HCD)	- A VO₂max test on cycle ergometry - A TTE test at 60–65% VO₂max at two time points: after HCD and K-LCHF diet	↔ VO₂max ↔ TTE performance ↑ Fat oxidation ↔ Blood glucose levels during TTE performance	[20]
Recreational athletes (n = 5)	Case study	K-LCHF diet (ad libitum FAT, <50 g CHO, 1.75 g protein/kg BW/d)	10 weeks	- A TTE performance - A peak power test - A VO₂max test	↓ TTE performance ↑ Fat oxidation during exercise even at higher intensities ↓ Body mass ↓ Skinfold thickness	[21]
Endurance-trained male athletes (n = 8)	A randomized, repeated-measures, crossover study	K-LCHF diet (75–80% FAT, <50 g CHO, 15–20% protein), HCD (43% CHO, 38% FAT, 19% protein)	4.5 weeks	- A graded metabolic test to exhaustion - A TTE performance at 70% VO₂max	Preservation of mucosal immunity ↑ Both pro- and anti-inflammatory T-cell-related cytokine responses to a multiantigen in vitro	[22]
Elite race walkers (n = 25)	A mix of repeated-measures and parallel-group design	K-LCHF diet (n = 10; 75–80% FAT, <50 g CHO, 17% protein), HCD (n = 8; 60–65% CHO, 2% FAT, 15–20% protein), or PCD, (n = 7; 60–65% CHO, 20% FAT, 15–20% protein)	3.5 weeks	- A graded walking economy and VO₂peak test - A 10-km track race After CHO re-adaptation: - A 20-km race walking	↔ VO₂peak ↓ 10 km race walk performance ↑ Perceived exertion after exercise ↑ Oxygen cost ↑ Whole-body fat oxidation	[23]
Male ultra-endurance runners (n = 20)	A cross-sectional study design	K-LCHF diet (n = 10, 10:19:70) diet or Habitual high-CHO (n = 10, %CHO:protein:fat = 59:14:25) diet	An average of 20 months (range 9–36 months)	- A graded exercise test - A 3-h run at 65% VO₂max on a treadmill	↑ Fat oxidation ↔ Muscle glycogen utilization and repletion after 180 min of running and 120 min of recovery	[24]
Male competitive recreational distance runners (n = 7)	A randomized counterbalanced, crossover design	K-LCHF diet (n = 10; 75–80% FAT, <50 g CHO, 17% protein), or HCD (n = 8; 60–65% CHO, 20% FAT, 15–20% protein)	6 weeks	- A VO₂max test - A 5-km TT performance (day 4, 14, 28, and 42)	↔ VO₂max ↔ TT performance ↑ Fat oxidation	[25]
Endurance-trained male cyclists (n = 5)	Crossover design	A high-fat diet (70% FAT) or an equal-energy, high-carbohydrate diet (70% CHO)	2×2 weeks, 2 week washout period in between (ad libitum diet during washout period)	- Peak power output test - A cycling exercise to exhaustion at 90% VO₂max, 20-min rest, and followed with a cycling exercise to exhaustion at 50% VO₂max	↑ TTE performance during MIE ↔ Endurance performance during HIE ↑ Fat oxidation	[26]
Highly trained male ultra-endurance runners (n = 20)	A cross-sectional study design	Habitual low CHO (n = 10; <20% CHO, >60% FAT) or high CHO (n = 10; >55% CHO)	At least 6 months		↑ Circulating total cholesterol, LDL-C, and HDL-C concentrations ↑ Fewer small, dense LDL-C particles	[27]
Trained male off-road cyclists (n = 8)	A crossover design	A mixed diet (%CHO:fat:protein = 50:30:20) or a NK-LCHF diet (15:70:15)	4 weeks	A continuous exercise protocol on a cycling ergometer with varied intensity (90 min at 85% LT, then 15 min at 115% LT)	↑ VO₂max ↓ Body mass ↓ Body fat percentage ↑ Fat oxidation ↓ Post-exercise muscle damage ↓ CK and LDH concentration at rest and during the 105 min exercise protocol in the NK-LCHF diet trial	[28]
Endurance trained cyclists (n = 16)	A randomized, controlled study design	A NK-LCHF diet (19:69:10) or a habitual diet (%CHO:fat:protein = 53:30:13)	15 days	a 2.5-h constant-load ride at 70% VO₂peak followed by a simulated 40-km cycling TT while ingesting a 10% 14C-glucose + 3.44% MCT emulsion at a rate of 600 mL/h	↑ Fat oxidation ↔ TT performance	[29]
Trained male cyclists (n = 9)	A repeated-measures, randomized, crossover study	2 × 0.35 g/kg KE or placebo (30 min before and 60 min after exercise)	Acute ingestion	A 85-min steady state exercise at 73% VO₂max, followed by a 7 kJ/kg TT (~ 30 min)	↑ Transient type-I T-cell immunity at the gen level	[30]
Endurance-trained male and female athletes (male/female, 9/3)	A single-blind, randomized and counterbalanced, crossover design	KE (330 mg/kg BW of βHB containing beverage, or bitter-flavored placebo drink before exercise	Acute ingestion	An incremental bicycle ergometer exercise test to exhaustion	↔ Blood pH and HCO₃ levels ↔ TTE performance	[31]
Endurance-trained athletes (male/female:5/1)	A single-blind, random order controlled, crossover design	A 400 mL, low-dose β-HB KME 252 mg/kg BW, “low ketosis”; a high-dose βHB KME (752 mg/kg BW, “high ketosis”, or a bitter-flavored water (placebo)	Acute ingestion, 60 min prior to exercise	A 60-min continuous cycling exercise, consisting of 20 min intervals at 25%, 50% and 75% Wmax	↓ Contribution of exogenous βHB to overall energy expenditure ↑ Exercise efficiency when blood βHB levels above 2 mmol/L ↑ Nausea	[32]
High-performance athletes	Study 1: A randomized crossover design Study 2, 3 and 5: A randomized, single-blind, crossover design Study 4: A two-way crossover study	Study 1 (n = 6): A KE (573 mg/kg BW) drink at rest, and during 45 min of cycling exercise 40% and 75% of WMax; with 1 week washout period in between Study 2 (n = 10): - 96% of calories from CHO (dextrose = CHO), KE (573 mg/kg BW), or FAT before test Study 3 (n = 8): - 60% of calories from CHO and 40% of KE (573 mg/kg BW), a mixture of carbohydrates (CHO), or a no-calorie beverage with 1000 mg B3 before test Study 4 (n = 7): - 60% of calories from CHO (dextrose) and 40% from KE, or a mixture of CHOs, 50% of the drink consumed at baseline, the remaining 50% at 30 min, 60 min, and 90 min during exercise as equal aliquots Study 5 (n = 6 male, n = 2 female): - 60% of calories from CHO and KE (573 mg/kg BW), or a mixture of carbohydrates (CHO)	Acute ingestion	Study 1: - A 45-min cycling exercise at 40% and 75% WMax Study 2 and 3: - A fixed-intensity cycling exercise at 75% WMax for 60 min Study 4: - A fixed-intensity bicycle ergometry test at 70%VO₂max for 2-h Study 5: - A 60-min steady state workload at 75% WMax followed by a blinded 30-min TT	↑ TT performance following 1 h of high-intensity exercise ↑ Fat oxidation ↓ Plasma lactate levels during exercise ↑ D-βHB oxidation according to exercise intensity (from 0.35 g/min at 40% WMax to 0.5 g/min at 75% WMax) ↔ Blood glucose levels	[33]
Trained male cyclists (n = 9)	A repeated-measures, randomized, crossover study	A drink containing 0.35 g/kg BW BD or placebo	Acute ingestion (30 min before and 60 min during 85 min of steady state exercise)	A steady state cycling at the power output eliciting 85% of their VT followed by a TT performance equivalent to 7 kJ/kg (~25–35 min)	↔ TT performance and average power output ↔ Blood glucose and lactate levels ↑ Fat oxidation ↑ GI symptoms	[34]
Elite male cyclists (n = 10)	A randomized crossover design	A 1,3-butanediol AcAc diester (2×250 mg/kg BW) or a viscosity and color-matched plasebo drink	Acute ingestion, ~30 min before and immediately prior to commencing the warm up	~A 31-km laboratory-based TT performance on a cycling ergometer	↓ TT performance ↑ GI symptoms (nausea and reflux) ↑ Fat oxidation	[35]
Male runners (n = 11)	A randomized crossover design	An energy matched ∼650 mL drink containing 60 g CHO + 0.5 g/kg BW 1.3-butanediol (CHO-BD) or 110 g ± 5 g CHO alone	Acute ingestion (50% after baseline measurements + 25% after 30 min of seated rest, + 25% after 10 min rest period after completing submaximal running)	A 60-min submaximal running, followed by a 5-km running time trial	↔ TT performance ↔ Overall lactate concentration ↑ Blood glucose levels after TT performance ↑ Fat oxidation	[36]
Highly trained male cyclists (n = 12)	A randomized crossover design	A KE drink (65 g (918,102 mg/kg, range: 722–1072 mg/kg) of KE [ 96% βHB] or a viscosity- and taste-matched placebo	Acute ingestion (at 60 and 20 min before and at 30 min during race)	A simulated cycling race, which consisted of a 3-h intermittent cycling, a 15-min time trial, and a maximal sprint	↔ High-intensity exercise performance in the final stage of the event ↑ Upper-abdominal discomfort ↓ Appetite after exercise ↔ Net muscle glycogen breakdown	[37]
Recreational male distance runners (n = 13)	A randomized, double-blind, placebo-controlled, cross- over design	Either one (KS1: 22.1 g) or two (KS2: 44.2 g) servings of the ketone supplement (βHB + MCT) or a flavor-matched placebo drink	Acute ingestion (60 min prior to exercise)	A 5-km running TT on a treadmill	↔ Post-exercise glucose concentration ↔ TT performance ↔ Perceived exertion after exercise Dose–response impact on cognitive function	[38]
Eight trained, middle- and long-distance runners (male/female, 7/1)	A double-blind, randomized crossover design	An 8% carbohydrate-electrolyte solution before and during exercise, either alone (CHO + PLA), or with 573 mg/kg of a ketone monoester supplement (CHO + KME)	Acute ingestion	A 60-min submaximal exercise at 65%VO₂max immediately followed by a 10-km TT	↔ TT performance ↔ VO₂max, running economy, RER, HR, perceived exertion ↔ Cognitive performance ↔ Plasma glucose and lactate levels ↑ Fat oxidation	[39]
Male and female elite race walkers	A non-randomized clinical trial	A K-LCHF diet (n = 18; 75–80% FAT, <50 g CHO, 15–20% PRO) followed by an acute CHO restoration, or HCD (n = 14; 60–65% CHO, 20% FAT, 15–20% PRO)	3.5 weeks	A hybrid laboratory/field test of 25 km (males) or 19 km (females) at around 50 km race pace at 75% VO₂max	↓ Bone resorption markers at rest and post-exercise ↑ Bone formation markers at rest and throughout exercise Partial recovery of these effects following CHO restoration	[40]
Well-trained competitive male cyclists or triathletes (n = 7)	A randomized, crossover design	Day 1: a standard CHO diet (%CHO:fat:protein = 58:27:15) Day 2–7: either an HFD (16:69:15) or HCD (70:15:15) for 6 days Day 8: HCD (70:15:15)	6 day fat adaptation followed by 1 day CHO restoration, a 18 day washout period between	Day 9: A 4-h cycling ergometer at 65% VO₂peak, followed by a 60-min TT	↔ TT performance ↑ Fat oxidation	[41]
Well-trained competitive male cyclists or triathletes (n = 8)	A randomized, crossover design	Day 1–5: either an HFD (%CHO:fat:protein = 19:68:13) or an HCD (74:13:13) Day 6: HCD (74:13:13)	5 day fat adaptation followed by 1 day CHO restoration, a 2 week washout period between	A 2-h cycling at 70% VO₂max; followed by 7 kJ/kg TT	↔ TT performance ↑ Fat oxidation ↔ Muscle glycogen utilization ↔ Plasma glucose uptake	[42]
Well-trained competitive male cyclists or triathletes (n = 8)	A randomized, double-blind crossover design	Day 1–5: either an HFD (%CHO:fat:protein = 19:68:13) or an HCD (74:13:13) Day 6: HCD (74:13:13) Pre-exercise: a CHO breakfast (CHO 2 g/kg). During exercise: CHO intake (0.8 g/kg/h)	5 day fat adaptation followed by 1 day CHO restoration, a 2 week washout period between	A 2-h cycling at 70% VO₂max; followed by 7 kJ/kg TT	↔ TT performance ↑ Fat oxidation	[43]
Well-trained competitive male cyclists or triathletes (n = 8)	A randomized, double-blind crossover design	Day 1–5: either an HFD (%CHO:fat:protein = 19:68:13) or an HCD (74:13:13) Day 6: HCD (74:13:13)	5 day fat adaptation followed by 1 day CHO restoration, a 2 week washout period between	A 60-min steady state ride at 70% VO₂max	↓ Muscle glycogen utilization ↑ Fat oxidation ↑ Pre-exercise AMPK-1 and AMPK-2 activity ↓ Exercise-induced AMPK-1 and AMPK-2 activity	[44]
Endurance-trained male cyclists (n = 8)	A randomized, single-blind, crossover design	Day 1–6: either a NK- LCHF diet (%CHO:fat:protein = 16.8:68.2:15.0) or an HCD (67.8:17.1:15.1) Day 6: HCD (16.8:68.2:15.0)	6 day fat adaptation followed by 1 day CHO restoration, a 2 week washout period between	A 100-km TT on their bicycles; five 1 km sprint distances after 10, 32, 52, 72, and 99 km, four 4 km sprint distances after 20, 40, 60, and 80 km	↔ TT performance ↑ Fat oxidation ↓ 1 km sprint power ↔ Perceived exertion	[45]
Endurance-trained male cyclists (n = 5)	Randomized, crossover design	Either 10 day habitual diet (~30% fat), followed with 3 day HCD or 10 day high-fat diet (> 65% fat), followed by 3 day HCD 1 h prior to each trial: −400 mL 3.44% MCT (C_8–10) solution During trial: 600 mL/h 10% glucose (¹⁴C) + 3.44% MCT solution	10 day HFD + 3 day HCD vs. 10 day habitual diet + 3 day HCD - Acute ingestion of MCT solution 1 h before trial and glucose + MCT solution during trial	A 150-min cycling at 70% VO₂peak, followed immediately by a 20-km TT	↑ TT performance ↑ Fat oxidation ↓ Muscle glycogen utilization ↔ Body fat, BW	[46]
Endurance-trained male cyclists or triathletes (n = 7)	A randomized, double-blind crossover design	Day 1–5: either an HFD (%CHO:fat:protein = 19:68:13) or an HCD (74:13:13) Day 6: HCD (74:13:13)	5 day fat adaptation, a 2 week washout period between	A 20-min steady state cycling at 70% VO₂peak, 1 min rest, a 1 min all-out sprint at 150% PPO, and followed by 4 kJ/kg TT	↑ Fat oxidation ↓ Glycogenolysis and PDH activation ↔ Muscle glycogen contents at rest	[47]
A lacto-ovo vegetarian athlete who adhered to an LCHF diet for 32 weeks	Case study	An LCHF diet for 32 weeks	32 weeks	Three professional races while on the LCHF diet in week 21, 24, and 32 (consumption of CHO before and during the race as advised)	↓ Half-ironman performance at week 21 ↓ Ironman performance at week 24 and 32 ↔ Exercise-induced GI symptoms	[48]
Trained male cyclists (n = 11)	A reference-controlled crossover (two treatment, two period), balanced, masked, single-center outpatient metabolic trial	HCD (% CHO:protein:fat = 73/14/12) for 2.5 days or HCD for first day and followed by the last 1.5 days with fat-enriched feeding (43/9/48)	2.5 days (1 day HCD, followed by lipid supplementation for 1.5 day), or 2.5 day HCD	Pre- and post-intervention; - A 3-h exercise on a bicycle ergometer at 50% Wmax post-intervention; - 20-km TT	↔ Perceived exertion after exercise ↔ Fat oxidation during prolonged exercise ↑ Replenishment of both glycogen content and IMCL stores ↔ TT performance	[49]
Trained male cyclists (n = 22)	A single-blind (clinical trial staff were blinded), 2-treatment crossover randomized clinical trial	An HCD, (CHO 7.4 g/kg BW, FAT 0.5 g/kg BW) for 2.5 days or a high-CHO fat-supplemented (HCF) diet ((first day similar with HCD, followed by 1.5 days with a replication of the HC diet with 240 g surplus fat (30% saturation)) distributed over the last 4 meals of the diet period	2.5 days (1 day HCD, followed by lipid supplementation for 1.5 day), or 2.5 day HCD	A fixed-task simulated TT lasting approximately 1-h A VO₂peak test	↔ TT performance ↔ Fat oxidation during submaximal or 1 h TT exercise ↔ Reaction time throughout TT	[50]
Male collegiate long-distance athletes (n = 8)	A double-blind, placebo- controlled, crossover study design	3 days before the trial: an HCD (% CHO:fat:protein = 71:19:10) 4 h before exercise: HF meal (% CHO:fat:protein = 30:55:15) or HC meal (% CHO:fat:protein = 70:21:9) Immediately before exercise: - either maltodextrin jelly (M) or a placebo jelly (P) in the HF meal group - a P in the HC group	Acute ingestion (either HF meal or HC meal 4 h before exercise)	An 80-min fixed-load test on a treadmill at ~70 VO₂max, followed with continuous endurance running to exhaustion at ~80% VO₂max	↑ TTE performance in pre-exercise HF meal plus M consumption after CHO-loading ↑ Fat oxidation	[51]
Vegetarian Diets
Vegan (n = 24), LOV (n = 26) and omnivorous (n = 26) recreational runners	A cross-sectional study design	Omnivorous, LOV or vegan diet for at least half a year	At least 6 months	An incremental exercise test on a bicycle ergometer	↔ maximum power output ↔ Exercise capacity ↔ Blood lactate and glucose concentration during incremental exercise	[52]
Vegan (n = 23), LOV (n = 25) and omnivorous (n = 25) recreational runners	A cross-sectional study design	Omnivorous, LOV or vegan diet for at least half a year	At least 6 months	An incremental exercise test on a bicycle ergometer	↑ exercise-induced MDA concentration in the vegan (+15% rise) and LOV (+24% rise) groups ↔ NO metabolism	[53]
Male endurance athletes (n = 8)	A crossover design	A mixed meat-rich diet (69% animal protein sources) or a LOV diet (82% vegetable protein sources)	2 ×6 weeks, 4 week washout period in between (ad libitum diet during washout period)	- A VO₂max test	↔ Immunological parameters ↑ Fiber intake ↑ P/S ratio of fatty acids ↔ VO₂max capacity	[54]
Omnivorous, lacto-ovo vegetarian, and vegan recreational runners (21–25 subjects, respectively)	A cross-sectional study	Omnivorous, lacto-ovo-vegetarian or vegan diet for at least half a year	At least 6 months	An incremental exercise test on a bicycle ergometer	↑ exercise-induced MDA concentration ↓ Sirtuin activities in vegans	[55]
A male vegan ultra-triathlete and a control group of 10 Ironman triathletes	Case report	A vegan ultra-triathlete adhered to a raw vegan diet and a control group of 10 Ironman triathletes adhered to a mixed diet	Vegan athlete living on a raw vegan diet for 6 years, vegan for 9 years and a vegetarian for 13 years	A Triple-Ironman distance (11.4 km swimming, 540 km cycling, and 126 km running)	↑ VO₂max ↔ Exercise performance ↔ Exercise capacity ↔ Systolic and diastolic functions	[56]
A female vegan mountain biker	Case report	A vegan athlete living on a vegan diet for approximately 15 years	A vegan diet for approximately 15 years	The Transalp Challenge 2004 (altitude climbed, 22.500 m; total distance, 662 km, lasts approximately 8 days)	Successfully completing ultra-endurance mountain biking with a well-planned and implemented vegan diet	[57]
Vegetarian (n = 27) and omnivore (n = 43) elite endurance athletes	Cross-sectional study design	Vegetarian and omnivore endurance athletes who adhered to their respective diets for at least three months	At least three months	A VO₂max test on the treadmill	↔ Exercise performance ↔ Protein intake (kg BW/day) ↑ VO₂max (in females) ↔ VO₂max (in males)	[58]
Vegan (n = 22) and omnivorous (n = 30) amateur runners	Cross-sectional study design	Vegan and omnivore athletes; diet adherence time not reported	-	VO₂max and peak power output test on the treadmill	Better systolic and diastolic function ↑ VO₂max	[59]
Intermittent Fasting Diets
Well-trained, middle-distance runners (n = 18)	A non-randomized, controlled study	RIF vs. control	1 month	Beginning and at the end of Ramadan: - A VO₂max test on the treadmill - A MVC testing - A 5-km TT	↓ TT exercise performance ↔ VO₂max ↔ Running efficiency	[60]
Middle-distance athletes (n = 8)	Pre–post-test	RIF	1 month	5 days before, 7 and 21 days after Ramadan: - A maximal aerobic velocity test	↓ Nocturnal sleep time ↓ Energy intake ↔ BW and body fat percentage ↔ Testosterone/cortisol ratio ↑ Fatigue ↑ Transient alteration in circulating IL-6, adrenaline, noradrenaline levels	[61]
Elite under 23 cyclists (n = 16)	Parallel randomized trial	Time-restrictive eating (TRE) (16 h fasting, 8 h eating periods) or normal diet; both the same energy and macronutrient composition	4 weeks	Pre- and post-diet: - A VO₂max test - A 45-min cycling ergometer at 45% peak power output	↔ VO₂max ↔ endurance performance ↑ PPO/BW ratio ↓ BW and body fat percentage ↔ Fat-free mass	[62]
Male trained cyclists (n = 11)	A non-randomized repeated-measures experimental study design	Ramadan fasting (15 h 15 min fasting period)	29 days	A slow progressively increasing training load period (endurance training at first, and then intensity training included progressively)	↑ Perceived exertion ↑ DOMS ↔ Total sleep time ↓ duration of deep and REM sleep stages ↔ Cognitive performance	[63]
Adolescent male cyclists (n = 9)	A partially double-blind, placebo-controlled, randomized design	A CHO mouth rinse (with 25 mL of the solution) (CMR), a placebo mouth rinse (PMR), and a no-rinse (NOR) trial during Ramadan fasting state (fasting period ~13.5 h)	The last two weeks of Ramadan	A cycling exercise at 65% VO₂peak for 30 min followed by a 10 km TT under hot (32 °C) humid (75%) condition	↑ TT performance in the CMR and PMR groups ↓ Perceived exertion in the CMR compared to the NOR ↔ Total sleep time	[64]
Trained male middle- and long-distance runners (n = 17)	A randomized, parallel-group, pre-and post-experimental design	A TRE (fasting: 16 h, ad libitum eating: 8 h) (n = 10) or normal diet (n = 7)	8 weeks	An incremental test until exhaustion	↓ BW ↔ VO₂max ↔ Running economy ↔ Blood lactate, glucose, and insulin ↓ Daily energy intake	[65]
Gluten-Free Diet
Non-coeliac or non-IBS competitive endurance cyclists (n = 13)	A controlled, randomized, double-blind, crossover study design	GFD or gluten-containing diet plus additional 2 gluten-free or gluten-containing food bars (total 16 g wheat gluten per day)	2 × 7 days, a 10 day washout period in between	A steady state cycling at 70% Wmax for 45 min followed by a 15 min TT	↔ TT performance ↔ GI symptoms ↔ Intestinal damage ↔ Well-being	[66]
Low-FODMAP Diet
Recreationally competitive runners with non-clinical GI symptoms (5 males, 6 females)	A single-blind, crossover design	Either a high-FODMAP or a low-FODMAP (<0.5 g FODMAP/meal) diet	2×6 days, 1 day washout period in between	- A 5 × 1000-m run on day 4 - A 7-km threshold run on day 5	In the low-FODMAP group; ↔ Well-being ↓ GI symptoms	[67]
A female ultra- endurance runner	Case study	A 4 week low-FODMAP diet, (3.9 g FODMAP/day)	4 week low-FODMAP diet + 6 week reintroduction of high-FODMAP foods	A 6-day 186.7 km multistage ultra-marathon	Minimal GI symptoms ↑ Nausea ↓ Energy, protein, CHO, and water intake compared to the recommended guidelines	[68]
A recreationally competitive multisport athlete	Case study; a single-blind approach	A 6 day low-FODMAP diet (7.2 ± 5.7g FODMAPs/day) vs. habitual diet (81 ± 5 g FODMAPs/day)	6 days	Same training period both diet trial (Swim 60 min (day 1); cycle 60 min (day 2); rest (day 3); run intervals 70 min (day 4); cycle 180 min and steady state run 65 min (day 5) and; run intervals 65 min (day 6))	↓ Exercise-induced GI symptoms	[69]
Endurance runners (n = 18)	A double-blind randomized crossover design	A high- (46.9 ± 26.2 g FODMAP/day) or low- (2.0 ± 0.7 FODMAP/day) FODMAP diet	2 × 1 day; before each experimental trial	A 2-h running at 60% VO₂max in 35 °C ambient temperature	In the low-FODMAP group; ↓ Exercise-associated disruption of GI integrity ↓ Exercise-associated GI symptoms ↓ Breath H₂ concentration	[70]

↓: A significant decrease after the diet manipulation in the experimental group; ↑: A meaningful rise after the diet manipulation in the experimental group; ↔: No change after the diet manipulation in the experimental group. Abbreviations: K-LCHF: ketogenic low-carbohydrate, low-fat diet; NK-LCHF: non-ketogenic low-carbohydrate, low-fat diet CHO: carbohydrate; HCD: high-carbohydrate diet; TT: time trial; CPT: critical power test; s-IgA: serum immunoglobulin A; Wmax: maximal power output; VO₂peak: peak oxygen uptake; VO₂max: maximal oxygen uptake; PCD: periodized carbohydrate diet; TTE: time-to-exhaustion; MIE: moderate intensity exercise; HIE: high-intensity exercise; LDL-c: low-density lipoprotein; HDL-c: high-density lipoprotein; CK: creatine kinase; LDH: lactate dehydrogenase; SS: steady state; HCO₃: hydrogen bicarbonate; KE: ketone ester; KME: ketone monoester; BW: body weight; βHB: (R)-3-hydroxybutyl (R)-3-hydroxybutyrate); VT: ventilatory threshold; GI: gastrointestinal; MCT: medium-chain triglycerides; RER: Respiratory exchange ratio; HR: heart rate; IMCL: Intra myocellular lipid; LOV: lacto-ovo-vegetarian; MDA: malondialdehyde; NO: nitric oxide; P/S ratio: polyunsaturated/saturated fatty acid ratio; MVC: Maximal Voluntary Isometric Contraction; IL-6: interleukine-6; PPO/BW ratio: peak power output/body weight ratio; DOMS: delayed onset muscle soreness; GFD: gluten-free diet; FODMAP: fermentable oligosaccharides, disaccharides, monosaccharides and polyols.