How to practise fuelling for long runs

Start with the goals

Fuelling during a long run has two direct aims: maintain available energy and avoid ending early because of dehydration or gut discomfort. Performance is an indirect outcome. For sustained running beyond about an hour, carbohydrate and fluid choices before, during and after the run can all affect the experience; the actual need depends on duration, intensity, weather, sweat rate and personal tolerance.

A sports-nutrition position stand notes that the timing and amount of carbohydrate intake around exercise can affect performance and recovery, and that guidance should be individualised to the exercise demand and overall diet. What follows is therefore a method for testing, not a dose table for everyone.

Test in training, not on race day

Race day is no time to debut a new gel, drink or breakfast. Treat each long run as a small experiment:

1. Change one or two variables: for example, "a small carbohydrate portion every 40 minutes" or "swap to an electrolyte drink". Do not change everything at once.
2. Record intake and response: timing, product or food type, amount, weather, pace, and how your stomach, mood and late-run performance responded.
3. Repeat: use the same approach in two or three similar long runs before deciding it suits a race.
4. Keep an exit: if nausea, bloating or diarrhoea appears, reduce the amount or return to a familiar option. Seek professional advice if problems persist.

A practical carbohydrate approach

Eat normally before training; do not make chronic fasting the default for long runs. During the run, start small and take carbohydrate at planned intervals rather than waiting for an obvious energy crash and then eating a large amount. Options include sports drinks, gels, chews, bars or easy-to-digest real food. The key is that you can take it while moving and that your gut accepts it.

When reading labels, compare the carbohydrate actually consumed per serving or per hour, not the number of packets. Products vary widely in concentration and volume, so copying someone else's "packets per hour" is meaningless. Some runners tolerate a mix of carbohydrate sources better, but that still needs personal testing.

Fluid and electrolytes

Fluid needs vary with temperature, humidity, altitude, sweat rate and the individual. There is no single millilitre target that fits everyone. A simple everyday reference is urine colour: pale yellow generally suggests reasonable hydration. During exercise, stomach comfort and access to toilets also matter. The NHS notes that people may need more fluid when physically active for long periods or in a hot environment.

When sweat losses are large, a sodium-containing drink or electrolyte tablet may help, but cramps should not be reduced to "low sodium". If you have kidney or heart conditions, or have been advised to restrict salt, follow medical advice for fluid and electrolyte plans.

Caffeine and other supplements

Caffeine may help some endurance athletes, but dose, timing and individual response vary and it can affect sleep. Do not try a high dose for the first time on race day. Treat other supplements the same way: look at the evidence, the conditions of use and the race rules before deciding. This article recommends no brand or dose.

After the run and recovery

Return to normal eating soon after a long run, prioritising carbohydrate and protein, and drink according to thirst. For the broader picture, see what to do on a recovery day. If gastrointestinal problems, dizziness or unusual palpitations recur during long runs, stop the approach and seek medical advice.

Sources and scope

This article draws on the International Society of Sports Nutrition position stand on nutrient timing and the NHS guidance on water and hydration. It is general sports-nutrition education, not medical advice, and does not apply to people who need individual nutrition therapy. It was checked on 2026-10-27.