Carbohydrate

Summary

What is it? Carbohydrate here means sugars and starches taken in a drink, gel or food during exercise to give the body energy. So far this page covers one question: endurance exercise in the heat.

Why would I need it? Hard exercise uses up the body's stored carbohydrate, called glycogen, and heat may use it up faster. Athletes who race or train in hot weather want to know whether drinking carbohydrate helps them last longer.

Is it useful? Possibly, but in the heat the results are inconsistent. A 2026 systematic review of 9 small trials found that carbohydrate drinks clearly improved cycling performance in 5 trials and made no clear difference in 4 ^{[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}. Across all conditions, a 2024 meta-analysis of 136 studies found an overall benefit ^{[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}. The two findings do not match, and heat-specific evidence is limited to young, mostly male cyclists tested in laboratories.

FAQ

Does carbohydrate help endurance performance in the heat? Not consistently. In 5 of 9 trials, cycling time to exhaustion rose by 13.4% to 19.3%, or time-trial performance improved by 3.3% to 12.7%. In the other 4 trials the difference was not statistically significant ^{[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 the result different in cool weather? A 2024 meta-analysis of 136 studies found a significant overall gain in endurance performance with carbohydrate, and it did not find that dose or carbohydrate type changed the size of the gain. Its abstract does not split results by temperature ^{[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}.

Does more carbohydrate work better? Not in the heat trials. A 14% drink given at about 140 g per hour was followed by shorter time to exhaustion than placebo (24.5% shorter, p = 0.09, not significant) ^{[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}. Only 2 of the 9 trials measured stomach and gut symptoms, so the reason is unknown ^{[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 cause stomach problems? It can. In one 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 change body temperature or hydration? In the review, carbohydrate did not change core temperature in 7 of 8 trials that measured it, and it did not change hydration markers in most 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}.

Article

What it is

Carbohydrate taken during exercise comes as sports drinks, gels or food. The 9 trials in the 2026 review used drinks in 8 cases and a sago porridge in 1 ^{[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 evidence says in the heat

A 2026 systematic review pooled no numbers, because the 9 trials were too different. It reported each result on its own ^{[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}. All 9 were randomised crossover trials, in which each person took both carbohydrate and placebo on different days. They had 6 to 16 participants each, all cycled in climate chambers at 27 to 35 °C, and most participants were young men ^{[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 intake ranged from 14 to 140 g per hour, and the exercise lasted about 50 to 152 minutes ^{[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}. Five trials found a significant gain. Two of them used a 6.4% maltodextrin drink at about 58 g per hour, and time to exhaustion rose by 13.4% to 19.3% ^{[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}. Four trials found no significant effect. Separately, the authors point to three studies whose non-significant average gains of 6.7% to 11.6% (in some drink groups) could still matter to elite athletes ^{[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 also reports that carbohydrate did not change core temperature in 7 of 8 trials, did not change perceived effort in 6 of 7, and did not clearly change hydration ^{[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 spare the body's glycogen?

Most of the 9 trials found no difference in how much carbohydrate the body burned. The authors read this as a sign that the body relied on its own glycogen even when it was fed carbohydrate. No trial used tracers to confirm it ^{[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 separate 2026 meta-analysis of 31 studies, not limited to the heat, found a small but significant glycogen-sparing effect of carbohydrate (standardised difference -0.16, 95% CI -0.30 to -0.02) ^{[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}.

Doses used in the heat trials

Limits of this evidence

1. Few small trials. Nine trials with 6 to 16 people each, and 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}.
2. Narrow group. Mostly young, well-trained men. The results may not apply to women, older people or heat-acclimatised athletes ^{[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}.
3. Laboratory cycling only. No running, and no field trials. Seven of the 9 trials 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}.
4. 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}.
5. Risk of bias. The review rated all 9 trials "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}.
6. Different tests. Time to exhaustion tests are less repeatable than time trials, and the trials differ in meals, drinks and duration ^{[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}.
7. 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}.

Talk to a doctor before you start a supplement, especially if you take medicines or are pregnant.

Verification

Checked on 2026-11-10.