Running and marathon nutrition, built around your training

At a glance

• Energy demands: High, rising sharply in marathon blocks
• Key fuel: Carbohydrate, matched to mileage and sessions
• Race-day risk: Gut upset and late glycogen depletion
• Health watch: Low energy availability and bone stress

What running asks of your body

Running demands vary hugely with distance. A 5k or 10k is run close to maximal aerobic effort and is over quickly, so the priority is arriving fresh and well fuelled rather than eating during the race. The marathon is a different problem: at goal pace, most runners rely heavily on muscle and liver glycogen, and when those stores run low in the final third, pace drops sharply. This is what runners call hitting the wall.

Training is built around weekly mileage, with easy runs, a long run, tempo or threshold work and intervals. As a marathon block builds, energy and carbohydrate needs climb, often faster than appetite does. Running is also a weight-bearing, high-impact sport, so repeated under-fuelling tends to show up not only as heavy legs but as bone stress injuries, frequent illness and stalled progress.

The gut is a bigger performance factor in running than in most endurance sports. The jolting action, reduced blood flow to the gut at higher intensity and race-morning nerves make cramps, urgency and nausea common. Pre-race meals, gels and drinks need practising in training, at race pace, so that race day feels familiar rather than experimental.

Nutrition priorities for runners

Match carbohydrate to mileage

Runners training 1–3 h a day at moderate to high intensity typically need around 6–10 g/kg/day of carbohydrate, with less on easy and rest days. We periodise this around your long run and key sessions. [1]

Rehearse marathon race fuelling

For races of 1–2.5 h, 30–60 g/h of carbohydrate is the usual guide. Runners on their feet for longer than 2.5–3 h may benefit from up to 90 g/h using glucose–fructose products, built up gradually in long runs. [1]

Train the gut

Gut tolerance improves with practice. We plan which long runs and race-pace sessions to rehearse gels, drinks and timing in, and change products if symptoms persist.

Protect bone health

Repeated low energy availability raises the risk of bone stress injuries and other RED-S consequences, especially in runners under pressure to be light. We screen for warning signs and put fuelling training first. [2]

Recover between quality runs

Spread protein through the day, with about 0.3 g/kg after key sessions, alongside carbohydrate to restock glycogen before your next interval or tempo run. [1]

Hydrate for race conditions

Aim to avoid losing more than 2% of body mass through sweat, particularly at warm spring marathons. Weighing before and after long runs helps us estimate your losses without encouraging you to over-drink. [1]

Marathon race-day fuelling

1. 36–48 hours before: Carbohydrate loading at around 10–12 g/kg/day over the final 36–48 h tops up glycogen for the marathon. Lower-fibre choices help many runners keep their gut settled. [1]
2. Race morning: Eat a familiar breakfast providing 1–4 g/kg of carbohydrate 1–4 h before the start, using the amount and timing you rehearsed before long runs. [1]
3. During the race: Take carbohydrate at regular intervals from early on, aiming for 30–60 g/h, or up to 90 g/h if you will be running for longer than 2.5–3 h and have trained your gut. [1]
4. After the finish: Start with fluids, carbohydrate and about 0.3 g/kg protein once you can face food, then return to regular meals. The days after a marathon are for recovery, not restriction. [1]

General guidance from sports nutrition consensus statements. Your practitioner will tailor amounts to you.

Race distances and their demands

5k and 10k

Short and intense, so in-race fuelling is rarely needed; the focus is a well-timed pre-race meal and day-to-day fuelling for interval training.

Half marathon

Long enough that a little carbohydrate during the race can help, particularly for runners finishing in more than 90 minutes, and a carbohydrate-focused day before is worthwhile.

Marathon

Glycogen becomes the limiting factor, so carbohydrate loading, a rehearsed in-race plan and gut training are central.

Masters runners

Recovery and protein spread deserve more attention with age, alongside bone health as training load builds.

What we help with

• Hitting the wall in the final miles of a marathon
• Stomach cramps, urgency or nausea during races
• Constant hunger or fatigue during marathon training blocks
• Recurrent bone stress injuries or missed periods
• Pressure to be lighter affecting fuelling and health
• Choosing gels, drinks and caffeine without endless trial and error

Ongoing support, not one-off sessions

We do not work with athletes on a one-off basis. Sports nutrition works best when it adapts to your training, so we recommend an initial consultation followed by at least three follow-ups.

Who you could work with

• Jenaed Ruddock, HCPC-registered Sports Dietitian (SENr)
• Beatriz Ribeiro, HCPC-registered Dietitian
• Melissa Bosch, Eating Disorder Nutrition Specialist

Book your consultation

Book an initial consultation or book a free discovery call to talk it through first. All consultations are online.

Explore more

See all the sports we work with, our RED-S nutrition support, or meet the team.

Frequently asked questions

How much carbohydrate do I need when training for a marathon?

It depends on your mileage and the intensity of your sessions. As a guide, runners training 1–3 h a day typically need around 6–10 g/kg/day, with more on long-run days and less on easy days. We build a personalised plan from your training schedule rather than giving you a fixed number.

Should I carb load before a half marathon?

Full carbohydrate loading, at around 10–12 g/kg/day, is generally reserved for events lasting more than 90 minutes, so it suits marathoners and half-marathon runners who will be out for longer than that. Faster half-marathon runners usually do well with a carbohydrate-focused day before and a good breakfast. We help you decide based on your expected finish time.

Why do I get stomach problems when I run?

Running jolts the gut, and blood flow to the gut falls as intensity rises, so symptoms are common. Fibre or fat before the race, unfamiliar gels, dehydration and nerves can all add to the problem. We look at the pattern of your symptoms and build a gut-training plan, and recommend GP assessment if your symptoms suggest something beyond exercise-related upset.

Can a dietitian help if I keep getting stress fractures?

Yes. Bone stress injuries in runners are often linked to low energy availability, a central feature of RED-S. Our RED-S specialists assess your fuelling, training load and other warning signs, and recommend medical assessment where bone health or hormonal changes need investigating.

Can I book a single consultation before my marathon?

We do not work with athletes on a one-off basis. A marathon fuelling plan needs testing in long runs and adjusting as your mileage builds, so we recommend a minimum of three follow-up consultations after your initial consultation, spread across your training block.

Do you work with young runners?

These pages are for adult runners. Young runners are supported through our paediatric team, who tailor advice to growth, school and training.

References

1. Thomas DT, Erdman KA, Burke LM. Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and Athletic Performance. J Acad Nutr Diet. 2016;116(3):501–528.
2. Mountjoy M, et al. 2023 International Olympic Committee (IOC) consensus statement on Relative Energy Deficiency in Sport (REDs). Br J Sports Med. 2023;57(17):1073–1097.