High-carbohydrate diet
In elite race walkers, 10 km race times improved about 5% to 7% over 3 weeks of training on a high-carbohydrate diet and did not improve on a ketogenic diet. Meta-analyses of other trials found little difference in aerobic capacity. Muscle glycogen rose with higher intake. Cohorts in the general population link intakes above 70% of energy to higher mortality.
- Status
- A dietary pattern, not a regulated product.
- Also called
- high-carb diet, high carb diet, high-carbohydrate diet for athletes, carb loading, carbohydrate loading, glycogen loading, high-carbohydrate low-fat diet, HCHO
- Followed for
- endurance performance, race preparation, glycogen stores, training quality during hard blocks, mood and fatigue during heavy training
Strong several reviews agree · Moderate one review or consistent trials · Limited one or a few small studies · Untested no study in people, listed with what it rests on
Shown to help3
- ModerateShown to raise muscle glycogen when daily carbohydrate rose above 6.5 g per kg, with wide variation between studies.
- LimitedOne small crossover trial in trained runners found less performance loss and less fatigue during a week of intensified training on 8.5 g per kg of carbohydrate a day.
- LimitedOne trial in elite race walkers found 6 days of a ketogenic diet raised hepcidin, IL-6 and cortisol responses to exercise, while the high-carbohydrate group did not change.
What people follow it for, and what was found
Shown to help3
Muscle glycogen
Shown to raise muscle glycogen when daily carbohydrate rose above 6.5 g per kg, with wide variation between studies.
Compared with lower carbohydrate intakes, under 6.5 g per kg a day [7]
The numbers and sources
- Effect
- Raising carbohydrate intake from under 6.5 to over 6.5 g per kg a day increased muscle glycogen by 191.9 mmol per kg dry mass (95% CI 142.8 to 241.1, I² 94%). Glycogen tracked relative carbohydrate intake in recreationally active people (r² 0.332) and endurance-trained people (r² 0.490) [7].
- Population
- 63 trials with 641 participants described and 18 pooled, randomized and non-randomized, all with muscle biopsies [7].
- Sources
- [7]
- Caveats
- Heterogeneity was very high, and the review included non-randomized trials [7]. Glycogen is a fuel store, not a performance outcome.
Performance and mood during intensified training
One small crossover trial in trained runners found less performance loss and less fatigue during a week of intensified training on 8.5 g per kg of carbohydrate a day.
Compared with 5.4 g per kg a day of carbohydrate, in the same runners [8]
The numbers and sources
- Effect
- During intensified training, 8 km run times slowed 61 s on 8.5 g per kg a day of carbohydrate and 155 s on 5.4 g per kg a day. 16 km times slowed 8.2% only on the lower intake. Fatigue scores were higher, and global mood scores worse, on the lower intake [8].
- Population
- 7 trained runners with VO2max of 64.7 mL/kg/min, two 11-day trials [8].
- Sources
- [8]
- Caveats
- Seven people over 11 days [8].
Iron and stress markers after exercise
One trial in elite race walkers found 6 days of a ketogenic diet raised hepcidin, IL-6 and cortisol responses to exercise, while the high-carbohydrate group did not change.
Compared with a ketogenic low-carbohydrate high-fat diet and a low-energy diet, each group measured against its own baseline, in elite race walkers [10]
The numbers and sources
- Effect
- After 6 days, the ketogenic group showed larger exercise rises in IL-6, hepcidin, white blood cells and cortisol than at baseline, and blood glucose fell after exercise. The high-carbohydrate control group and a low-energy group did not change on any marker [10].
- Population
- 28 elite male race walkers [10].
- Sources
- [10]
- Caveats
- Six days, markers only. The authors describe the changes as small [10].
Mixed results1
Endurance performance against low-carbohydrate high-fat diets
Mixed results: elite race walkers improved more on high-carbohydrate than ketogenic diets, while meta-analyses found little difference in aerobic capacity or time to exhaustion.
Compared with a ketogenic low-carbohydrate high-fat diet and a periodized carbohydrate diet, in elite race walkers [1], [2]; a ketogenic low-carbohydrate high-fat diet, in elite race walkers [3]; high-fat diets [4]; ketogenic low-carbohydrate high-fat diets [5]; low-carbohydrate and ketogenic diets [6]
The numbers and sources
- Effect
- Over 3 weeks of intensified training, 10 km race walk times improved 6.6% on a high-carbohydrate diet and 5.3% on a periodized carbohydrate diet, with no improvement (-1.6%) on a ketogenic low-carbohydrate high-fat diet [1]. A repeat study found 10,000 m times improved 4.8% on high carbohydrate and slowed 2.3% on the ketogenic diet [2]. After 5 to 6 days on each diet, all high-carbohydrate walkers improved their race times (5.7%), while 6 of 7 ketogenic walkers were slower [3]. Across 20 trials, high-carbohydrate diets let people exercise longer to exhaustion (effect size 0.60), with an effect of 0.05 in trained subjects and 2.84 in untrained subjects [4]. Across 10 studies in endurance athletes, ketogenic diets did not change VO2max or time to exhaustion [5]. A 2026 review of 33 studies found time to exhaustion maintained in 69.2% of studies on low-carbohydrate diets and economy impaired in half [6].
- Population
- 29 elite male and female race walkers [1]; 26 elite race walkers [2]; 13 world-class male race walkers [3]; trained and untrained subjects in 20 trials [4]; endurance athletes in 10 studies [5]; trained athletes aged 18 to 45 in 33 studies [6].
- Sources
- [1], [2], [3], [4], [5], [6]
- Caveats
- The race walk studies are small and come from one research group. Heterogeneity was significant in [4]. The 2026 review counted studies by direction instead of pooling effects, and found impairment within the first week and maintained or improved performance after it [6]. The ketogenic diet raised oxygen cost at race speeds by about 5% to 8% [3].
Not shown to help1
Against periodized carbohydrate restriction
Not shown to differ in performance from periodized carbohydrate restriction in trained endurance athletes.
Compared with a periodized carbohydrate diet, in elite race walkers [1]; periodized carbohydrate restriction in some training sessions [9]
The numbers and sources
- Effect
- Across 9 training studies, doing some sessions with restricted carbohydrate did not change endurance performance against training with normal high carbohydrate availability (SMD 0.17, 95% CI -0.15 to 0.49) [9]. In race walkers, a periodized diet improved 10 km times 5.3%, against 6.6% on constant high carbohydrate [1].
- Population
- Endurance-trained athletes with VO2max of at least 55 (women) or 60 (men) mL/kg/min, in interventions of a week or more [9]; elite race walkers [1].
- Sources
- [1], [9]
- Caveats
- Nine studies [9].
How trials defined it
The race walk trials fed 8.6 g per kg of carbohydrate, 2.1 g per kg of protein and 1.2 g per kg of fat a day, with carbohydrate before, during and after training, for about 3 weeks, against a ketogenic diet under 50 g a day of carbohydrate with 78% of energy from fat [1][2]. A shorter trial used 9.7 g per kg a day of carbohydrate against the same ketogenic limit for 5 to 6 days [3]. Another used 65% of energy from carbohydrate as its high-carbohydrate control [10]. The runner trial compared 8.5 g per kg a day (65% of energy) with 5.4 g per kg a day (41%) [8]. The glycogen review classed over 6.5 g per kg a day as high, in trials that fed carbohydrate for at least 24 hours before a muscle biopsy [7]. The 2026 review defined low carbohydrate as 130 g a day or less, or 25% of energy or less [6].
Risks
Reported risks1
Long-term mortality at very high carbohydrate intake
Linked to higher all-cause mortality at very high carbohydrate intakes in cohort studies of the general population, not of athletes.
The numbers and sources
- Effect
- In cohorts with 432,179 participants, intake above 70% of energy from carbohydrate was linked to higher mortality than moderate intake (HR 1.23, 95% CI 1.11 to 1.36), with the lowest risk at 50% to 55% [11]. In 135,335 people in 18 countries, the highest fifth of carbohydrate intake was linked to higher total mortality (HR 1.28, 95% CI 1.12 to 1.46) and not to cardiovascular disease [12].
- Population
- 15,428 US adults aged 45 to 64 followed for a median of 25 years, pooled with 7 other cohorts [11]; adults aged 35 to 70 followed for a median of 7.4 years [12]. All observational.
- Sources
- [11], [12]
- Caveats
- Observational studies of usual intake from food questionnaires, not trials. Mortality depended on what replaced carbohydrate [11]. No study here measured athletes.
Claims tested and not found
- That a ketogenic block followed by restored carbohydrate gives a performance rebound. After 2.5 weeks back on high carbohydrate, race walkers who had been keto-adapted showed no better 20 km performance [2].
- That periodized carbohydrate restriction improves performance beyond a high-carbohydrate diet. Across 9 studies in trained athletes, performance did not differ [9].
Sources
- Burke LM, Ross ML, Garvican-Lewis LA, et al. Low carbohydrate, high fat diet impairs exercise economy and negates the performance benefit from intensified training in elite race walkers. The Journal of Physiology. 2017. https://doi.org/10.1113/jp273230
- Burke LM, Sharma AP, Heikura IA, et al. Crisis of confidence averted: Impairment of exercise economy and performance in elite race walkers by ketogenic low carbohydrate, high fat (LCHF) diet is reproducible. PLOS ONE. 2020. https://doi.org/10.1371/journal.pone.0234027
- Burke LM, Whitfield J, Heikura IA, et al. Adaptation to a low carbohydrate high fat diet is rapid but impairs endurance exercise metabolism and performance despite enhanced glycogen availability. The Journal of Physiology. 2020. https://doi.org/10.1113/jp280221
- Erlenbusch M, Haub M, Munoz K, et al. Effect of high-fat or high-carbohydrate diets on endurance exercise: a meta-analysis. International Journal of Sport Nutrition and Exercise Metabolism. 2005. https://doi.org/10.1123/ijsnem.15.1.1
- Cao J, Lei S, Wang X, et al. The Effect of a Ketogenic Low-Carbohydrate, High-Fat Diet on Aerobic Capacity and Exercise Performance in Endurance Athletes: A Systematic Review and Meta-Analysis. Nutrients. 2021. https://doi.org/10.3390/nu13082896
- Gawelczyk M, Kaszuba M, Zając A, et al. Effects of Low-Carbohydrate and Ketogenic Diets on Aerobic Performance in Trained Athletes: A Systematic Review and Meta-Analysis. Nutrients. 2026. https://doi.org/10.3390/nu18050740
- Jones RO, Areta JL, Fortis HO, et al. Dietary Carbohydrate Intake and Skeletal Muscle Glycogen: A Systematic Review and Meta-Analysis to Determine Optimal Carbohydrate Loading Strategies. Scandinavian Journal of Medicine & Science in Sports. 2026. https://doi.org/10.1111/sms.70379
- Achten J, Halson SL, Moseley L, et al. Higher dietary carbohydrate content during intensified running training results in better maintenance of performance and mood state. Journal of Applied Physiology. 2004. https://doi.org/10.1152/japplphysiol.00973.2003
- Gejl KD, Nybo L. Performance effects of periodized carbohydrate restriction in endurance trained athletes: a systematic review and meta-analysis. Journal of the International Society of Sports Nutrition. 2021. https://doi.org/10.1186/s12970-021-00435-3
- McKay AKA, Peeling P, Pyne DB, et al. Six Days of Low Carbohydrate, Not Energy Availability, Alters the Iron and Immune Response to Exercise in Elite Athletes. Medicine & Science in Sports & Exercise. 2021. https://doi.org/10.1249/mss.0000000000002819
- Seidelmann SB, Claggett B, Cheng S, et al. Dietary carbohydrate intake and mortality: a prospective cohort study and meta-analysis. The Lancet Public Health. 2018. https://doi.org/10.1016/s2468-2667(18)30135-x
- Dehghan M, Mente A, Zhang X, et al. Associations of fats and carbohydrate intake with cardiovascular disease and mortality in 18 countries from five continents (PURE): a prospective cohort study. The Lancet. 2017. https://doi.org/10.1016/s0140-6736(17)32252-3