Carbohydrate for endurance exercise in the heat: what the evidence says
Summary
What is it? A look at whether carbohydrate taken during exercise (as a drink, gel or food) improves endurance performance for people exercising in the heat. The main source is a 2026 systematic review of 9 randomised crossover trials [1]Carbohydrate supplementation for endurance exercise in the heat: a systematic review with practical recommendations. Salame A, Brown D, Oueijan K, et al. J Int Soc Sports Nutr, 2026.
Why would I need it? Heat makes hard exercise harder, and it may make the body use up its stored carbohydrate faster. Athletes who train or race in hot weather want to know whether drinking carbohydrate helps them keep going [1]Carbohydrate supplementation for endurance exercise in the heat: a systematic review with practical recommendations. Salame A, Brown D, Oueijan K, et al. J Int Soc Sports Nutr, 2026.
Is it useful? Possibly, but not reliably. In the review, 5 of 9 trials found a significant gain (time to exhaustion up 13.4% to 19.3%, or time trials 3.3% to 12.7% better), and 4 found no significant effect [1]Carbohydrate supplementation for endurance exercise in the heat: a systematic review with practical recommendations. Salame A, Brown D, Oueijan K, et al. J Int Soc Sports Nutr, 2026. The trials were small, were all done in laboratories on cyclists, and mostly used young men. The authors conclude that carbohydrate does not consistently improve performance in the heat [1]Carbohydrate supplementation for endurance exercise in the heat: a systematic review with practical recommendations. Salame A, Brown D, Oueijan K, et al. J Int Soc Sports Nutr, 2026.
FAQ
Does carbohydrate improve performance when it is hot? Sometimes. In the 2026 review, 5 of 9 trials found that carbohydrate beat placebo, and 4 found no significant difference [1]Carbohydrate supplementation for endurance exercise in the heat: a systematic review with practical recommendations. Salame A, Brown D, Oueijan K, et al. J Int Soc Sports Nutr, 2026. A 2024 meta-analysis of 136 studies in all conditions found an overall gain, so the heat results are less consistent than the general picture [2]The ergogenic effects of acute carbohydrate feeding on endurance performance: a systematic review, meta-analysis and meta-regression. Ramos-Campo DJ, Clemente-Suárez VJ, Cupeiro R, et al. Crit Rev Food Sci Nutr, 2024.
How much carbohydrate did the helpful trials use? Two trials used a 6.4% maltodextrin drink at about 58 g per hour and saw time to exhaustion rise by 13.4% to 19.3%. Another found an 18.5% gain with a 6% drink at about 43 g per hour (p = 0.045). A 16% drink at about 90 g per hour improved a 15-minute time trial by 12.7% [1]Carbohydrate supplementation for endurance exercise in the heat: a systematic review with practical recommendations. Salame A, Brown D, Oueijan K, et al. J Int Soc Sports Nutr, 2026.
Can too much carbohydrate hurt? It may. One trial gave a 14% drink at about 140 g per hour. Time to exhaustion was 24.5% shorter than with placebo, but the difference was not significant (p = 0.09) [1]Carbohydrate supplementation for endurance exercise in the heat: a systematic review with practical recommendations. Salame A, Brown D, Oueijan K, et al. J Int Soc Sports Nutr, 2026. In another trial, a 12% glucose drink at about 99 g per hour caused more nausea, fullness and stomach upset than a 6% drink or placebo [1]Carbohydrate supplementation for endurance exercise in the heat: a systematic review with practical recommendations. Salame A, Brown D, Oueijan K, et al. J Int Soc Sports Nutr, 2026.
Does carbohydrate make you hotter or more dehydrated? The review found no consistent effect. Core temperature did not differ in 7 of 8 trials, and one trial found a higher rectal temperature with carbohydrate. Only 2 of 7 trials that checked hydration found a difference [1]Carbohydrate supplementation for endurance exercise in the heat: a systematic review with practical recommendations. Salame A, Brown D, Oueijan K, et al. J Int Soc Sports Nutr, 2026.
Does it make exercise feel easier? Mostly not in the heat. Six of 7 trials found no difference in perceived effort [1]Carbohydrate supplementation for endurance exercise in the heat: a systematic review with practical recommendations. Salame A, Brown D, Oueijan K, et al. J Int Soc Sports Nutr, 2026.
Article
What was studied
The review searched four databases up to 14 April 2026. It included trials in healthy, at least recreationally active adults aged 18 to 65 who ingested a carbohydrate product during continuous exercise lasting more than 30 minutes in a hot setting (above 23 °C), with a placebo comparison and a direct performance measure [1]Carbohydrate supplementation for endurance exercise in the heat: a systematic review with practical recommendations. Salame A, Brown D, Oueijan K, et al. J Int Soc Sports Nutr, 2026. The review was registered in advance, and it found 3151 records and included 9 trials [1]Carbohydrate supplementation for endurance exercise in the heat: a systematic review with practical recommendations. Salame A, Brown D, Oueijan K, et al. J Int Soc Sports Nutr, 2026. The authors did not pool the results, because the trials differed too much, and they described each result separately [1]Carbohydrate supplementation for endurance exercise in the heat: a systematic review with practical recommendations. Salame A, Brown D, Oueijan K, et al. J Int Soc Sports Nutr, 2026.
The 9 trials
| Item | What the review reports |
|---|---|
| Design | Randomised crossover, 9 trials; 6 to 16 participants each |
| People | Mostly young men; two trials included women; 4 trials reported that participants were not heat-acclimatised |
| Setting | Climate chambers, 27 to 35 °C, 20% to 78% humidity |
| Exercise | All cycling; 4 time-to-exhaustion tests, 5 steady rides followed by a time trial |
| Carbohydrate | Drinks in 8 trials (one with sago porridge); 14 to 140 g per hour |
| Placebo | A matched sweet drink in 7 trials, plain water in 1, nothing in 1 |
| Result | Significant gain in 5; no significant effect in 4 |
All rows are from the review [1]Carbohydrate supplementation for endurance exercise in the heat: a systematic review with practical recommendations. Salame A, Brown D, Oueijan K, et al. J Int Soc Sports Nutr, 2026.
What the dose results suggest
Gains appeared with drinks of 6% to 25% sugar, at about 43 to 90 g per hour. The two highest doses (about 99 and 140 g per hour) gave no gain, and the 12% drink caused stomach upset [1]Carbohydrate supplementation for endurance exercise in the heat: a systematic review with practical recommendations. Salame A, Brown D, Oueijan K, et al. J Int Soc Sports Nutr, 2026. The review notes that 140 g per hour is far above the usual advice of 30 to 60 g per hour for exercise of 1 to 2.5 hours, which it takes from other sources [1]Carbohydrate supplementation for endurance exercise in the heat: a systematic review with practical recommendations. Salame A, Brown D, Oueijan K, et al. J Int Soc Sports Nutr, 2026. The authors suggest, without testing it, that lower concentrations may suit hot conditions [1]Carbohydrate supplementation for endurance exercise in the heat: a systematic review with practical recommendations. Salame A, Brown D, Oueijan K, et al. J Int Soc Sports Nutr, 2026.
Why the results may differ
The authors list reasons: some trials lasted only about an hour, four trials gave a meal before exercise, time-to-exhaustion tests are less repeatable than time trials, and participants' heat acclimatisation was mostly not reported [1]Carbohydrate supplementation for endurance exercise in the heat: a systematic review with practical recommendations. Salame A, Brown D, Oueijan K, et al. J Int Soc Sports Nutr, 2026. A 2024 meta-analysis also found larger gains in time-to-exhaustion tests than in time trials [2]The ergogenic effects of acute carbohydrate feeding on endurance performance: a systematic review, meta-analysis and meta-regression. Ramos-Campo DJ, Clemente-Suárez VJ, Cupeiro R, et al. Crit Rev Food Sci Nutr, 2024.
Limits of this evidence
- Few small trials. Six to 16 people per trial, with no pooled analysis [1]Carbohydrate supplementation for endurance exercise in the heat: a systematic review with practical recommendations. Salame A, Brown D, Oueijan K, et al. J Int Soc Sports Nutr, 2026.
- Narrow group. Mostly young, well-trained men, and mostly not tested for heat acclimatisation [1]Carbohydrate supplementation for endurance exercise in the heat: a systematic review with practical recommendations. Salame A, Brown D, Oueijan K, et al. J Int Soc Sports Nutr, 2026.
- Laboratory cycling only. No running and no field trials, and 7 of 9 used a fan [1]Carbohydrate supplementation for endurance exercise in the heat: a systematic review with practical recommendations. Salame A, Brown D, Oueijan K, et al. J Int Soc Sports Nutr, 2026.
- Gut symptoms rarely measured. Only 2 of 9 trials recorded them [1]Carbohydrate supplementation for endurance exercise in the heat: a systematic review with practical recommendations. Salame A, Brown D, Oueijan K, et al. J Int Soc Sports Nutr, 2026.
- Risk of bias. All 9 trials were rated "some concerns", mainly because no analysis plan was published before the data were unblinded [1]Carbohydrate supplementation for endurance exercise in the heat: a systematic review with practical recommendations. Salame A, Brown D, Oueijan K, et al. J Int Soc Sports Nutr, 2026.
- Mostly drinks. The review says little about gels or solid food [1]Carbohydrate supplementation for endurance exercise in the heat: a systematic review with practical recommendations. Salame A, Brown D, Oueijan K, et al. J Int Soc Sports Nutr, 2026.
- Funding and ties. The authors state that there was no funding and no conflict of interest [1]Carbohydrate supplementation for endurance exercise in the heat: a systematic review with practical recommendations. Salame A, Brown D, Oueijan K, et al. J Int Soc Sports Nutr, 2026.
What the authors suggest
The authors advise athletes in the heat to focus on staying hydrated, eating well before exercise, restoring glycogen afterwards and practising "gut training", meaning getting the gut used to taking carbohydrate during exercise. They base this on the wider literature, not on these trials [1]Carbohydrate supplementation for endurance exercise in the heat: a systematic review with practical recommendations. Salame A, Brown D, Oueijan K, et al. J Int Soc Sports Nutr, 2026. This is the authors' view, not advice for you.
Talk to a doctor before you start a supplement, especially if you take medicines or are pregnant.
Verification
Checked on 2026-11-10.
| Claim | Result | What the check found |
|---|---|---|
| In the heat, carbohydrate gave a clear gain in 5 of 9 trials and none in 4 | Not verified | No second review of heat trials was found. A PubMed search for reviews on carbohydrate in the heat returned only this one [1]Carbohydrate supplementation for endurance exercise in the heat: a systematic review with practical recommendations. Salame A, Brown D, Oueijan K, et al. J Int Soc Sports Nutr, 2026 |
| Carbohydrate improves endurance performance in general | Verified | A 2024 meta-analysis of 136 studies found a significant overall gain. Read as abstract only [2]The ergogenic effects of acute carbohydrate feeding on endurance performance: a systematic review, meta-analysis and meta-regression. Ramos-Campo DJ, Clemente-Suárez VJ, Cupeiro R, et al. Crit Rev Food Sci Nutr, 2024 |
| Gains are larger in time-to-exhaustion tests than in time trials | Verified | The 2024 meta-analysis found a larger effect in time to exhaustion. In the heat review, 3 of 4 such trials were significant, against 2 of 5 time trials. Read as abstract only [2]The ergogenic effects of acute carbohydrate feeding on endurance performance: a systematic review, meta-analysis and meta-regression. Ramos-Campo DJ, Clemente-Suárez VJ, Cupeiro R, et al. Crit Rev Food Sci Nutr, 2024 |
| A very high dose (about 140 g/h) lowered performance | Not verified | One trial only, and not significant (p = 0.09). The 2024 meta-analysis found that dose did not change the effect size, but its abstract does not mention doses this high [2]The ergogenic effects of acute carbohydrate feeding on endurance performance: a systematic review, meta-analysis and meta-regression. Ramos-Campo DJ, Clemente-Suárez VJ, Cupeiro R, et al. Crit Rev Food Sci Nutr, 2024 |
| Carbohydrate may not reduce glycogen use in the heat | Contradicted | This is the authors' inference from breathing measurements, with no tracers. A 2026 meta-analysis of 31 studies in general conditions found a small significant sparing effect. It was not tested in the heat. Read as abstract only [3]Carbohydrate ingestion during prolonged exercise and net skeletal muscle glycogen utilization: a meta-analysis. Rothschild JA, Dudley-Rode H, Carpenter H, et al. J Appl Physiol (1985), 2026 |
| Carbohydrate did not change core temperature, perceived effort or hydration | Not verified | No second source on these outcomes in the heat was found [1]Carbohydrate supplementation for endurance exercise in the heat: a systematic review with practical recommendations. Salame A, Brown D, Oueijan K, et al. J Int Soc Sports Nutr, 2026 |
See also
Sources
Carbohydrate supplementation for endurance exercise in the heat: a systematic review with practical recommendations. Salame A, Brown D, Oueijan K, et al. J Int Soc Sports Nutr, 2026
Systematic review · About this source