Whether you're lining up for a half marathon, marathon, IRONMAN 70.3 or a full IRONMAN, there is one thing every endurance athlete has in common:

You need a reliable supply of energy, fluid and electrolytes if you want to perform at your best.

Race fueling isn't simply about taking a gel when you start feeling tired. It is a strategy designed to make sure your body has enough carbohydrate available to support energy production, enough fluid to manage the water lost through sweat, and enough electrolytes to help maintain fluid and electrolyte balance throughout the event.

Carbohydrate, hydration and electrolytes are all part of the same performance equation.

The science behind endurance fueling has also evolved. We now understand more about how carbohydrates are stored and used, how different carbohydrates are absorbed, how fluid moves between compartments in the body, and why hydration strategies need to be individualised rather than based on a one-size-fits-all formula.

The good news is that you don't need an overly complicated nutrition strategy.

You need to understand a few fundamental principles, then practise them until they become part of your race routine.

Here are five of the most important.

1. Start the race with your carbohydrate stores and hydration in a good place

One of the biggest mistakes athletes make is thinking about race-day fueling only once the race has started.

Your fueling strategy actually begins well before the start line.

Carbohydrate is stored in the body primarily as glycogen, particularly in your muscles and liver. During endurance exercise, muscle glycogen becomes an important source of energy, particularly as exercise intensity increases.

The longer and harder you exercise, the greater the demand for carbohydrate.

This is why the objective before a long endurance event isn't simply to "eat a big breakfast."

It is to arrive at the start with:

• Adequate carbohydrate availability
• Well-stocked glycogen stores
• Appropriate hydration
• Normal electrolyte balance
• A stomach that feels comfortable and ready to exercise

For longer endurance events, increasing carbohydrate intake in the days leading into the race can increase muscle glycogen stores and help support performance.

Hydration follows a similar principle.

You don't want to begin a long race already significantly dehydrated, but you also don't need to spend the morning drinking litres of water in an attempt to become "extra hydrated."

The goal is to start normally hydrated, with sufficient time for fluids consumed before the event to be absorbed and any excess to be excreted.

What should you eat?

Good pre-race carbohydrate sources include:

• Maple syrup
• Oats and porridge
• Rice
• Pasta
• Potatoes
• Bread and toast
• Cereals
• Bananas and other fruit
• Rice cakes
• Pancakes
• Other familiar carbohydrate-rich foods

The closer you get to the start, the more important digestibility and familiarity become.

A pre-race meal should generally be carbohydrate-rich while being relatively low in fat, fibre and anything else you know causes digestive problems.

What about low-GI versus high-GI carbohydrates?

This is where the science becomes particularly interesting.

The glycaemic index (GI) describes how quickly a carbohydrate-containing food raises blood glucose compared with a reference food.

Low-GI carbohydrates tend to produce a slower and more gradual rise in blood glucose, while high-GI carbohydrates produce a faster rise.

You will often hear that low-GI carbohydrates are automatically better before endurance exercise because they provide a more sustained release of energy.

The reality is more nuanced.

Research comparing low- and high-GI pre-exercise meals has not consistently demonstrated a performance advantage for low-GI meals.

That doesn't mean GI is irrelevant.

Instead, think about carbohydrate type in the context of timing.

Several hours before the start, foods such as oats, wholegrain bread, rice, potatoes or other slower-digesting carbohydrate sources can form part of a balanced meal.

As you get closer to the start, however, the priority shifts towards providing readily available carbohydrate while minimising the amount of food sitting in your digestive system.

This is where more easily digested, higher-GI carbohydrate sources can have a practical role.

So the goal isn't simply:

"Low GI = good, high GI = bad."

It is:

"Choose the right carbohydrate, at the right time, for the job."

2. Start fueling early and keep your carbohydrate intake regular

One of the most common fueling mistakes is reactive fueling.

An athlete starts the race feeling fantastic, doesn't eat for the first hour, then suddenly feels flat and reaches for carbohydrate when fatigue has already arrived.

The problem is that your body has been using carbohydrate from the beginning of the race.

Muscle glycogen is being progressively consumed, while maintaining blood glucose becomes increasingly important as exercise continues.

Carbohydrate consumed during exercise provides an additional source of fuel, supports carbohydrate oxidation and helps maintain blood glucose. It can also reduce the rate at which the body's own carbohydrate stores need to be used. 

This is why fueling should be proactive rather than reactive.

Don't wait until you're hungry, you feel flat, and your legs are starting to feel heavy.

Start early and keep the carbohydrate coming.

How often should you fuel?

For many athletes, consuming carbohydrate in relatively small amounts at regular intervals works well.

Rather than taking a large amount of carbohydrate once every hour, you might divide your target into smaller amounts every 15–30 minutes.

For example, if your target were 70g of carbohydrate per hour, you could think about that as approximately:

17g every 15 minutes, rather than trying to consume 70g in one hit.

This can make your fueling more consistent and can also make it easier to coordinate carbohydrate intake with your hydration.

How much carbohydrate?

For many endurance athletes, 35–70g per hour is a useful starting range for prolonged exercise.

As event duration increases, athletes who have trained their strategy can potentially move towards 70–90g per hour or more, particularly when using multiple transportable carbohydrates such as glucose and fructose. 

The key word is trained. Your race nutrition should be something you have rehearsed repeatedly in training.

3. Understand the relationship between carbohydrate, fluid and electrolytes

This is where endurance fueling becomes much more than simply counting grams of carbohydrate.

What you drink matters just as much as what you eat.

During exercise, your body loses water and electrolytes through sweat. The amount can vary dramatically between athletes and is influenced by:

• Exercise intensity
• Temperature
• Humidity
• Body size
• Clothing
• Acclimatisation
• Individual sweat rate
• Individual sweat sodium concentration

This is why there is no single "correct" amount of water that every athlete should drink per hour.

Your objective is to manage fluid losses without either becoming significantly dehydrated or drinking excessive amounts.

Current sports hydration guidance recommends individualising fluid intake according to sweat losses and environmental conditions rather than simply drinking as much as possible.

Why does carbohydrate concentration matter?

Your gut isn't simply a pipe that allows anything you consume to instantly enter your bloodstream.

Water and dissolved substances move through the gastrointestinal system according to concentration gradients and transport mechanisms.

This is where osmolality becomes relevant.

Osmolality describes the concentration of dissolved particles in a solution.

When you consume a very concentrated drink containing large amounts of carbohydrate and other dissolved substances, its osmolality can be relatively high.

That matters because water movement across cell membranes is influenced by differences in solute concentration.

In simple terms, if the fluid in your digestive system becomes significantly more concentrated than the surrounding body fluids, water can move in the direction of the higher solute concentration. This is one reason why an overly concentrated carbohydrate drink can sometimes contribute to gastrointestinal discomfort rather than simply delivering carbohydrate and water efficiently.

This is also why carbohydrate and hydration need to be considered together.

You don't necessarily want to maximise carbohydrate concentration in your drink.

You want to find a combination that allows you to deliver the carbohydrate you need while still providing fluid your body can absorb effectively.

This becomes particularly important when athletes are targeting high carbohydrate intakes.

You might therefore use a combination of:

• Carbohydrate drink
• Water
• Gels
• Chews
• Food-based carbohydrate
• other Electrolyte sources

rather than trying to put everything into one bottle.

Electrolytes: where does sodium fit?

Sodium is the primary electrolyte lost in sweat.

It plays an important role in maintaining fluid balance and is involved in nerve and muscle function.

Sodium and glucose are also involved in intestinal transport processes that help facilitate fluid absorption.

This is one reason carbohydrate-electrolyte drinks have long been used in endurance sport. 

But more sodium isn't automatically better.

Sweat sodium concentration varies considerably between individuals, as does sweat rate.

A heavy, salty sweater competing in a hot and humid environment may have very different electrolyte requirements from an athlete racing in cool conditions who loses relatively little sweat.

The objective is therefore not to consume a predetermined amount of sodium simply because you're racing.

It is to understand your individual losses and build a strategy around them.

4. Train your body to use the carbohydrate you give it

There's an important difference between eating carbohydrate and being able to effectively use carbohydrate as fuel.

Your body has several ways of producing energy during exercise, but as intensity increases, carbohydrate becomes increasingly important.

Carbohydrate stored as muscle glycogen is an important source of energy during exercise, while carbohydrate consumed during exercise can be absorbed into the bloodstream and provide an additional source of fuel.

This is why endurance athletes don't simply need to eat carbohydrate.

They need to train their bodies to use it effectively.

Your body adapts to the fuel you repeatedly give it

When you consistently train with carbohydrate available, you repeatedly ask your body to process, transport and utilise that carbohydrate while exercising.

Endurance training increases the muscle's capacity for glucose uptake and carbohydrate metabolism. At the same time, consistently consuming adequate carbohydrate around training helps maintain and replenish glycogen stores so carbohydrate is available when you need it.

In other words, you're not simply training your legs to keep moving.

You're training the entire system responsible for getting carbohydrate from your food to your working muscles and turning it into usable energy.

This is where race fueling becomes part of training

Some of your key training sessions should replicate the nutritional demands of race day.

Practise:

• The amount of carbohydrate you intend to consume per hour
• The frequency at which you consume it
• The combination of carbohydrate sources
• Your hydration rate
• Your electrolyte strategy
• Consuming carbohydrate while exercising at race intensity
• Replenishing carbohydrate stores after demanding sessions

The objective isn't simply to prove that you can tolerate a gel or sports drink.

It is to progressively prepare your body for the carbohydrate, fluid and electrolyte demands of competition.

Train your fueling timing too

If your race plan is to consume carbohydrate every 20 minutes, practise doing exactly that in training.

If you intend to take a gel with water, practise the combination.

If you're using a carbohydrate drink, understand how much carbohydrate you're actually getting from each bottle.

If you're racing for four, five or ten hours, you need to know what your fueling strategy looks like hour after hour.

Race nutrition should become automatic.

You shouldn't be doing mathematical calculations about carbohydrate and hydration while you're 30 kilometres into a marathon.

5. Understand cramps and dehydration, and don't oversimplify them

Few things can derail an endurance race faster than a painful muscle cramp.

For years, the common explanation was straightforward:

You became dehydrated → you lost electrolytes → you cramped.

The reality is considerably more complicated.

Research now suggests that exercise-associated muscle cramps are likely multifactorial, with muscle fatigue and altered neuromuscular control appearing to play an important role. Dehydration and electrolyte disturbances may contribute in some circumstances, but they are not the sole explanation for cramps.

This distinction matters. It means that drinking more water or consuming more electrolytes isn't a guaranteed way to prevent cramping.

However, maintaining appropriate fluid and electrolyte balance remains an important part of an overall endurance strategy, particularly during prolonged exercise, in hot conditions and for athletes with high sweat losses.

Why does dehydration matter?

As you lose water through sweat, your total body water decreases.

This can reduce plasma volume and increase cardiovascular and thermoregulatory strain. As dehydration becomes more significant, maintaining exercise performance becomes increasingly difficult, particularly in the heat. 

At the same time, sweat contains sodium and other electrolytes.

Losing fluid without replacing any of it can therefore progressively alter both your hydration status and electrolyte balance.

But the answer isn't simply: "Drink as much as possible."

Over-drinking can be dangerous too.

Consuming excessive amounts of low-sodium fluid during prolonged exercise can contribute to exercise-associated hyponatremia, where blood sodium concentration becomes dangerously diluted.

So effective hydration sits between two extremes:

Don't arrive dehydrated.
Don't become excessively dehydrated.
And don't over-drink in an attempt to prevent dehydration.

What should you actually do?

Start by understanding your own sweat rate.

One practical method is to weigh yourself before and after a representative training session, accounting for the fluid you consumed and urine produced.

This can give you an estimate of how much fluid you are losing per hour.

From there, you can build a more personalised hydration strategy.

The same principle applies to sodium. If you know you are a heavy sweater or have previously struggled with significant salt losses during long, hot sessions, sodium becomes a particularly relevant part of your plan.

But don't assume that every cramp means you need more electrolytes.

Pacing, muscular fatigue, conditioning, hydration, temperature and electrolyte balance can all interact.

Your job is to manage the factors you can control.

Putting It All Together: A Complete Race-Fueling Strategy

The best endurance fueling strategy isn't one-dimensional.

It's not simply: "How many gels should I take?"

It is a combination of carbohydrate + fluid + electrolytes + timing.

Think about your strategy in three stages.

Before the race: Prepare the system

Carbohydrate: Build adequate glycogen stores.

Hydration: Start normally hydrated.

Electrolytes: Ensure your normal diet and fluid intake are providing adequate electrolyte availability.

Timing: Eat your final substantial meal early enough to digest it comfortably, then use smaller, easily digested carbohydrate sources closer to the start if appropriate.

During the race: Keep everything moving

Carbohydrate: Start early and consume regularly.

Fluid: Drink consistently according to your individual sweat rate and environmental conditions.

Electrolytes: Replace an appropriate proportion of sodium and other electrolytes lost through sweat.

Timing: Don't wait for thirst, hunger or fatigue to become extreme before responding.

Think about your fueling as a schedule rather than a reaction.

For example:

Every 15–30 minutes → carbohydrate

Regularly throughout the hour → fluid

Across the event → electrolytes according to your individual needs

The exact quantities will vary, but the principle remains consistent.

After the race: Replenish what you've used

Your race doesn't finish when you cross the line from a fueling perspective.

You've depleted carbohydrate stores, lost fluid and electrolytes, and placed significant stress on your muscles.

Post-race nutrition therefore becomes the beginning of recovery.

Carbohydrate helps replenish glycogen stores, while protein supports muscle repair and adaptation. Fluid and electrolytes help restore the water and electrolyte losses accumulated during the event.

The faster you need to recover for another training session or competition, the more important the timing of this recovery nutrition becomes.

The Bigger Picture: Fueling Is About Consistency

Ultimately, good race fueling isn't about finding one perfect gel, one perfect breakfast or one magic electrolyte product.

It is about creating a consistent supply of energy and fluid throughout the event.

Think of it as managing four things:

1. Energy: Start with adequate carbohydrate stores and continue supplying carbohydrate during the race.

2. Timing: Start early and consume carbohydrate regularly rather than waiting until fatigue appears.

3. Hydration: Replace an appropriate amount of the fluid you are losing through sweat without either allowing excessive dehydration or overdrinking.

4. Electrolytes: Consider your individual sweat losses, particularly sodium, alongside your fluid strategy.

And remember that these four elements are connected.

A high carbohydrate intake needs to be considered alongside fluid.

Fluid replacement needs to be considered alongside sodium.

Sodium and carbohydrate influence fluid absorption.

And your ability to use carbohydrate effectively depends partly on how well you've trained your body to handle the demands you're placing on it.

That's why your race nutrition shouldn't be something you invent on race morning.

Train it. Test it. Refine it. Then execute it.

Two athletes can complete the same marathon and require very different fueling strategies. The right approach depends on body size, intensity, duration, training status, environmental conditions, sweat rate, sweat sodium concentration, gastrointestinal tolerance and individual preference.

The most effective fueling strategy is therefore not necessarily the one with the most complicated numbers.

It's the one you have practised, your body is prepared to use, and you can execute consistently when the race gets hard.

Whether your next challenge is a half marathon, marathon, IRONMAN 70.3 or full IRONMAN, the fundamental principles remain the same:

Start prepared.
Fuel early.
Fuel regularly.
Hydrate intelligently.
Replace electrolytes appropriately.
And train your body to use the fuel you give it.

Because endurance performance isn't just about how strong your legs are.

It's about having the energy, hydration and resilience to keep asking them to work.

This article is intended as general sports nutrition education and isn't a substitute for individual advice from an accredited sports dietitian or sports nutrition professional.