Carbohydrate and Heat: Why Individualised Fuelling Still Matters
Carbohydrate strategy is often reduced to a single question: how many grams should an athlete consume per hour? That number can be useful as a planning reference, but it is not a complete fuelling strategy—especially when racing in hot conditions.
The selected research in this week’s MCC Intelligence Report does not support a universal conclusion that increasing carbohydrate intake in the heat will consistently improve hydration, thermoregulation or performance. Findings across the available studies are mixed, and the evidence base has important limitations.
The heat changes the problem—but not in one predictable way
Heat increases physiological strain and can alter pacing, sweat losses, gastrointestinal comfort and the practical demands of fuelling. However, athletes do not respond identically. The outcome depends on factors such as exercise intensity, duration, environmental conditions, acclimatisation, body size, sweat rate, carbohydrate tolerance and the athlete’s existing strategy.
A fuelling plan that works during a moderate training ride may not work during a high-intensity race in humid conditions. Equally, an aggressive target copied from an elite athlete or online recommendation may exceed what another athlete can comfortably absorb.
What the evidence means in practice
The systematic review considered in the report found equivocal results across nine studies and no consistent benefit for hydration or thermoregulation from carbohydrate intake in the heat. A separate current-opinion review also challenges the idea that very high carbohydrate targets should be applied automatically to every athlete and event.
This does not mean carbohydrate is unimportant. Carbohydrate remains a key fuel source for many endurance efforts, particularly when intensity and duration rise. The point is that the strategy must match the demand and be tested by the individual rather than selected from a headline figure.
Questions athletes should ask
- How long will the event last?
- What intensity is realistic for the athlete?
- How hot and humid are the expected conditions?
- What carbohydrate sources can the athlete tolerate while moving?
- Has the strategy been practised during comparable training sessions?
- How will carbohydrate intake interact with fluid and sodium intake?
- What adjustments are needed if pace, conditions or gastrointestinal comfort changes?
Train the strategy, not just the fitness
Fuelling is a skill. Athletes should practise the products, quantities, timing and combinations they intend to use in competition. Training should also include representative conditions where possible, because heat, effort and gastrointestinal tolerance interact.
A sensible process is to start with a workable strategy, observe the athlete’s response, and make measured adjustments. The objective is not to chase the largest possible intake. It is to provide enough usable energy while maintaining comfort, pacing and race execution.
The MCC coaching perspective
The key principle is simple: coach the demand and the athlete, not the headline number. Research can inform the starting point, but individual response and practical testing determine whether the strategy is appropriate.
Source note: Verify the specific review titles, study populations and original source links before publication. The evidence summary should not be presented as a universal prescription.
Source:
Salame A, Brown D, Oueijan K, McCullough D. “Carbohydrate supplementation for endurance exercise in the heat: a systematic review with practical recommendations.” JISSN. 2026;23:2669307. https://pubmed.ncbi.nlm.nih.gov/42105255/ — systematic review supporting the article’s equivocal-performance and no-consistent-hydration/thermoregulation conclusions. Plews DJ, Booth PD, Krieger T, Maunder E. “Fuelled or Fooled? Examining the Evidence and Mechanisms Behind Ultra-High Carbohydrate Intake in Endurance Athletes.” Sports Medicine. 2026;56:2367–2388. https://pubmed.ncbi.nlm.nih.gov/42258036/ — review supporting caution against universal ultra-high carbohydrate targets.