Fuel the Fire: Can Carbohydrates Improve your Performance in the Heat?

At this time of year, many of us are training for marathons, entering cycling crits, or simply enjoying longer runs in the beautiful weather that we rarely experience in Britain. However, the warm weather brings its own challenges and exercising in the heat can be a challenge in itself. When the temperatures rise, your body isn't just working to feed your muscles, your body is also engaged with keeping you cool and staying hydrated. Therefore, your usual choice of nutrition may not work quite as well when the barometer starts to rise.

A recent review by Salame et al (2026) explored whether consuming carbohydrates during endurance exercise improves performance in heat. The evidence points to a resounding ‘yes’, but how much carbohydrates you consume is a key factor.

Carbohydrates are what the body prefers during prolonged periods of exercise. They help preserve the body’s glycogen stores, maintain blood glucose levels and delay fatigue. This allows athletes to maintain their performance for longer. And this role is undisputed when exercising in moderate temperatures. However, the heat can add an extra layer of complexity.

As the body’s temperature rises, it has to work harder to keep the athlete cool. As a result, blood is directed towards the skin as a kind of biological coolant. While this helps regulate the body’s temperature, it leaves less blood available for the stomach and intestines. So, digestion becomes slower creating all kinds of problems: reduced absorption of nutrients, a greater chance of gastrointestinal discomfort such as bloating, nausea, or stomach cramps. Alongside this, dehydration becomes a threat; this means that drinks must provide both fuel and fluid without causing the digestive system to become overwhelmed. However, if an athlete requires more hydration because of the heat, they may accidentally consume more carbohydrates than their body can absorb if they are using sports drinks alone. In these situations, it is better to treat hydration and carbohydrate intake as separate needs.

Salame et al (2026) analysed ten randomised crossover studies involving trained endurance athletes exercising in temperatures between 27°C and 35°C. Most participants were well-trained cyclists or runners with good levels of aerobic fitness. Half of the studies reported improvements in performance when the athletes consumed carbohydrates during exercise. Time-to-exhaustion improved by 13% to 19% and, impressively, time-trial performances improved from 3% to 13%. Also, researchers concluded that when athletes consumed a very concentrated 14% carbohydrate drink, the drink's high concentration caused stomach discomfort, making it harder for athletes to perform.

Discovering the Sweet Spot

The research identified practical guidelines that athletes and recreational exercisers can use. Sports drinks containing 6% to 8% carbohydrate consistently appeared to provide the best balance between delivering energy and maintaining digestive comfort. Drinks stronger than 12% carbohydrate are much more likely to cause stomach problems, especially in hot conditions where digestion is already slowed.

Don’t Chase the Social Media Headlines of Consuming 120g per Hour

For longer events and competitions, athletes often choose multiple-transportable carbohydrates, typically combinations of glucose and fructose; these allow the body to absorb more carbohydrates per hour than glucose alone. While these blends still offer advantages in the heat, the review suggests staying at the lower end of recommended intake, around 60 to 90 grams of carbohydrate per hour. Overwhelming the system can cause a biological traffic jam that renders the carbohydrate ineffective.

Do Carbohydrates Increase Your Body Temperature?

Research suggested that this is not the case. Nine out of ten studies conducted measured body temperature. Only one study found a minor increase in core temperature among athletes that consumed carbohydrates. Scientists conclude athletes should not avoid carbohydrates because of a concern they are worried they will overheat during their performance.

Gut Instincts: Practice Makes Perfect

The most interesting discovery from the review is that the digestive system often determines success in the heat. For endurance athletes, the gut needs to be trained as much as the heart, lungs and muscles. Practising carbohydrate intake during long training sessions, particularly in warm conditions, allows the digestive system to adapt and become more tolerant. Sports nutritionists recommend four to six weeks of gut training before important competitions. Practise taking carbohydrates on long runs and prior to hard training sessions. You should slowly build up to the required amount and consider what works best for you and your system.

Carbs: A Real Hot Topic

Heat places the body under stress but does not eliminate the benefits of carbohydrate supplementation. The evidence clearly suggests that athletes who consume moderate amounts of carbohydrates in appropriately diluted drinks can maintain performance without suffering digestive problems. Carbohydrate supplementation is required in hotter climates, but the million-dollar question is how to take the carbs in a way the body can handle. This is something that is often unique to every athlete.

Bibliography

Abbiss, C.R. et al. (2008). Study investigating carbohydrate supplementation, thermoregulation and endurance exercise in the heat.

Carter, J. et al. (1988). Effects of a 6.4% carbohydrate drink on endurance performance during exercise in hot conditions.

Che Jusoh, M.R. et al. (2010). Influence of pre-exercise feeding and carbohydrate supplementation during prolonged exercise in the heat.

Davis, J.M. et al. (1988). Effects of carbohydrate beverage concentration on gastrointestinal symptoms and endurance exercise performance.

Febbraio, M.A. et al. (1994, 1996). Studies examining carbohydrate concentration, hydration, gastrointestinal tolerance and endurance performance during exercise in the heat.

Flood, T.R. et al. (2020). Multiple-transportable carbohydrate ingestion and gastrointestinal responses during prolonged exercise in hot conditions.

Salame, H. et al. (2026). Carbohydrate supplementation for endurance exercise in the heat: A systematic review.Journal of the International Society of Sports Nutrition.