Marathon nutrition tips from our Sports Dietician

Isabella Alfonso

Isabella is a registered dietitian specialising in sports nutrition, with a holistic approach to supporting performance, health, and well-being. She has a particular interest in working with female athletes and is part of the RED-S clinic delivery team.

Looking to understanding your fueling needs or get your tailored fueling plan? Book your session with Isabella here.

The importance of ‘carb-loading’ before a marathon is widely known but did you know your daily carbohydrate intake in the weeks leading up to race day is just as important?

Carb needs by training volume

Your daily carbohydrate needs should reflect your training volume:

Training Duration	Recommended Carb Intake [1]
~1 hour/day	5–7 g/kg/day
1–3 hours/day	6–10 g/kg/day
4–5 hours/day	8–12 g/kg/day

Your diet should also include:

●      Protein and healthy fats for muscle repair and energy balance

●      Fiber-rich carb sources in your main meals for digestive and micronutrient support

Carbs fuel your training, reduce injury risk, and prepare your body for race-day performance [1]. It’s important to note, that whilst these are the recommendations, that even professional athletes often struggle to get in their recommended daily intake. One 2019 review found that 15 out of 17 studies reported athletes consumed 2.4–4.9 g/kg/day, which is below the minimum guideline of 5 g/kg/day.

Getting the balance right of having enough carbohydrates, protein and fats for your training, your specific body composition and to prevent injury can be tricky, we’d recommend speaking to our team to get some more insight into a nutrition plan that makes sense for you, as nutrition is never ‘one-size fits all’.

Carbohydrates are your body’s primary fuel during endurance exercise. You need to train with carbs to race with them efficiently.

During training (i.e. during your runs) and racing, guidelines recommend:

●      30–90 grams of carbs per hour for runs over 60 minutes

These can come from: sports drinks, gels, dried fruit, sweets, essentially, whatever works for your gut!

Gut training: why it matters

Your digestive system is trainable, just like your muscles.

Practicing your fueling strategy during training helps:

●      Improve carbohydrate absorption

●      Reduce risk of GI distress, cramping, or urgent bathroom stops

Trying something new on race day is risky. Stick with what your gut knows.

What about caffeine?

Many sports gels and drinks include caffeine to boost performance.

A pre-race dose of 3–6 mg/kg body weight can enhance endurance [4During long events, ~50 mg/hr can help sustain performance

⚠️ BUT caffeine can cause GI issues and a laxative effect in some individuals, this is why it’s important to test it in training first.

⚠️ General guidance: do not exceed 400 mg/day

Hydration & electrolyte tips

Start each session well-hydrated, and drink to thirst during training.

Most runners perform best when they avoid >2% body weight loss from sweat

You lose sodium through sweat, and replacing it helps prevent hyponatremia

The American  College of Sports Medicine recommends:

●      300–600 mg sodium/hour during prolonged exercis

Salt replacement can come from electrolyte drinks, tablets, or gels.

Why this matters:

If you don’t fuel and hydrate properly in training:

-       Increased risk of fatigue, cramps, or gut issues

-       Slower recovery

-       Unpredictable race-day performance

But when you train your nutrition like your mileage:

-       Better long runs

-       More reliable gut performance

-       Race-day confidence with a practiced fueling plan!

Looking to understanding your fueling needs or get your tailored fueling plan? Book your session with Isabella here.

References:

[1] Thomas DT, Erdman KA, Burke LM. (2016). 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.

[2]Jenner SL et al. Dietary Intakes of Professional and Semi‑Professional Team‑Sport Athletes Do Not Meet Sport Nutrition Recommendations — A Systematic Literature Review. Nutrients. 2019;11(5):1160. This review found the majority of athletes under-consumed carbohydrates compared to ISSN guidelines

[3] Jeukendrup AE. (2017). Training the Gut for Athletes. Sports Medicine.

[4] Burke LM, et al. (2013). Caffeine and Sports Performance. Appl Physiol Nutr Metab.

[5] EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA). (2015). Scientific Opinion on the safety of caffeine. EFSA Journal.

[6] Sawka MN, et al. (2007). Exercise and fluid replacement. ACSM Position Stand. Med Sci Sports Exerc.