Fuelling in the Heat

During exercise in the heat, the body must send blood to both the working muscles and the skin, where heat can be released. Dehydration can intensify this cardiovascular strain.

At the same time, high exercise intensity, heat stress and reduced blood flow to the gastrointestinal system can contribute to nausea, bloating, cramping and other GI symptoms — especially during prolonged endurance exercise.²

Heat can also change carbohydrate metabolism, although the effect is not identical in every situation. It depends on exercise intensity, whether workload or heart rate is matched, hydration, acclimation and the athlete's training status.¹

General endurance guidelines remain a useful starting point:

• Around 30–60 g of carbohydrate per hour for prolonged exercise.
• Up to approximately 90 g per hour for events lasting longer than 2.5–3 hours, using multiple transportable carbohydrates such as glucose and fructose.

These are starting ranges, not compulsory numbers. The appropriate target depends on duration, intensity, body size, experience, product choice and gastrointestinal tolerance.⁴

In the heat, the goal is usually not to abandon the carbohydrate target at the first sign of discomfort. The better strategy is to make delivery easier.

One of the most useful hot-weather adjustments is to avoid making one product perform every job.

A highly concentrated carbohydrate drink can provide substantial fuel, but it ties carbohydrate intake to thirst and fluid intake. In the heat, this creates two problems:

• Drinking more because you are thirsty may deliver more carbohydrate than your gut tolerates.
• Drinking less because the flavour becomes unpleasant may reduce both fluid and carbohydrate intake.

Use water and electrolytes to manage hydration; use gels, chews, drink mix or food to reach the carbohydrate target.

This does not mean carbohydrate drinks are unsuitable. It means knowing how much carbohydrate and fluid each serving provides, so one can be adjusted without accidentally losing control of the other.

A large carbohydrate dose may feel manageable in cool weather and overwhelming in the heat. Smaller servings taken more regularly are often easier to tolerate.

An athlete targeting 60 g per hour might divide it into:

• 20 g every 20 minutes, or
• 15 g every 15 minutes.

The hourly total is similar; each individual exposure is smaller. This is not a universal rule — the correct pattern is the one you have rehearsed successfully in hot training.

In warm conditions, athletes often become more sensitive to:

• excessive sweetness;
• thick textures;
• strong flavours;
• dry foods;
• large boluses;
• highly concentrated drinks.

A theoretically perfect product is not useful if the athlete stops consuming it after three hours. Build variety into the plan: mixed gel flavours, drink-based carbohydrate, chews, softer solids, neutral or savoury options, and plain water between sweet servings.

Glucose-fructose combinations can support higher carbohydrate delivery than glucose alone — but the product still needs to be tolerated and practised.¹

Do not assume that a cool-weather fuelling rehearsal proves hot-weather tolerance. Repeated carbohydrate practice during running has been shown to reduce gastrointestinal symptoms and carbohydrate malabsorption; roughly two weeks of gut training improved symptoms and running performance compared with placebo training.⁶⁷

The aim is progressive familiarity:

• Establish a tolerable intake in normal conditions.
• Practise the same plan during moderate heat.
• Test race products at race effort.
• Adjust serving size, texture and flavour.
• Rehearse fuel, water and electrolytes together.

A carbohydrate target is a tool, not a punishment.

During severe heat, pace often drops. Forcing a maximum carbohydrate intake through worsening nausea may not be productive.

Heat does not challenge only the gut. Sweat loss, dehydration, heavy mouth breathing and stress can reduce salivary flow — the remaining saliva becomes more concentrated, creating the familiar dry, sticky mouth of long hot efforts.⁸

At the same time, the athlete may be consuming:

• sweet gels;
• acidic sports drinks;
• concentrated chews;
• frequent carbohydrate servings;
• more fluid than usual.

The mouth becomes coated and overloaded by sweetness. Swallowing another gel feels increasingly unpleasant even when the athlete still needs the energy. This is where oral comfort becomes part of carbohydrate strategy.

UNBTN Oral Performance is not a carbohydrate product and does not replace water, sodium or cooling. Its role is narrower:

To stimulate natural saliva and support oral comfort between fuelling moments.

Use UNBTN when the mouth begins to feel dry, sticky, coated after repeated gels, overwhelmed by sweetness, or uncomfortable during prolonged mouth breathing.

Take planned fuel → drink as appropriate → use UNBTN between fuel servings → continue the nutrition plan.

UNBTN uses calcium-balanced HAp⁺, developed to stimulate saliva while remaining non-erosive under its validated testing conditions. It is sugar-free, so it does not add another conventional sweet between carbohydrate servings.

It should not be claimed that UNBTN prevents heat illness, hydrates the body, improves carbohydrate absorption, prevents GI distress, neutralizes every acidic gel, or guarantees an athlete can keep eating. Its value is practical:

Before

• Begin well fueled; avoid starting with an unnecessary fluid deficit.
• Prepare a primary carbohydrate target and a lower fallback target.
• Calculate fluid and electrolytes separately.
• Carry more than one flavour or texture, and a clear cooling plan.

During

• Steady intake from the beginning; small, familiar servings.
• Water according to thirst, plan and conditions; electrolytes to sweat losses.
• Cool whenever available. Respond early to oral or GI discomfort.

When tolerance falls

• Slow the next serving or take a smaller dose.
• Follow concentrated fuel with water; switch flavour or texture.
• Reduce unnecessary sweetness; cool the body.
• Use UNBTN between fuel servings for oral comfort.

Hot-weather fuelling is not simply the cool-weather plan with more water added. Heat changes pacing, circulation, thirst, gut tolerance, carbohydrate use and oral comfort.

The carbohydrate target still matters. But in the heat, execution matters more than the number written on the plan.

Fuel early. Separate fluid from fuel when useful. Use smaller familiar servings. Train the gut. Protect oral comfort. Adapt before the plan breaks.

Reset the mouth. Keep fuelling. Keep moving.