Nutrition for runners: what to eat from 10K to marathon

How much energy and how many carbohydrates do you need for your training?

Energy availability is the energy left for your body’s functions after exercise. If you increase your mileage without eating more, you may fall short even if your meals seem sufficient. Intense hunger at the end of the day, persistent tiredness or slow recovery are reasons to review your plan [2].

For light activity days, the guideline is 3–5 g/kg/day. The sports nutrition guide suggests around 5–7 g of carbohydrates per kilo of body weight per day for about an hour of moderate exercise [1]. For higher-volume endurance training, it recommends 6–10 g/kg/day [1]. With very high training loads, this can reach 8–12 g/kg/day. These are planning ranges, not targets to force without considering your training and health.

For someone weighing 70 kg, the first range is equivalent to 350–490 g of carbohydrates per day [1]. The second is 420–700 g [1]. These are carbohydrates from all foods, not grams of rice.

One meal might combine potatoes, bread, fruit and yoghurt; another might be rice with vegetables and egg. The sports nutrition guide explains how to spread your food intake around training.

What changes on long-run days?

A long run is also a chance to practise your fuelling. Note how long it lasts, what you have, how fast you run and how your stomach responds. Repeat the practice well ahead of time before changing amounts. A route with known water fountains and aid stations lets you plan without carrying more than you need.

Prepare dinner and your post-run meal with familiar foods. If you head out early, sort out the logistics the night before. For your pre-run meal and questions about fasting, see the athlete breakfast guide. Choose a combination you have tolerated during similar training sessions; do not try new recipes the night before a race.

How do you carbohydrate-load before a marathon?

Carbohydrate loading aims to start a long event with full muscle glycogen stores. The reference plan for efforts lasting more than 90 minutes is 10–12 g/kg/day during the 36–48 hours beforehand, together with a reduction in training [1].

For someone weighing 70 kg, that would be 700–840 g of carbohydrates per day [1]. The cited plan combines more carbohydrates with less training, without requiring a prior depletion phase [1].

This is a large amount. Spread it across meals and snacks, using familiar foods and simple preparations. Rice, pasta, bread, potatoes, fruit or yoghurt let you vary textures without relying on a single dish. If the volume causes discomfort, plan a workable strategy with a dietitian-nutritionist. The expected duration and your training, not just the distance, help determine whether carbohydrate loading beforehand makes sense [1].

What should you take during a long race?

The duration helps guide the amount of carbohydrates to have during exercise. For races lasting 1 to 2.5 hours, the guideline is 30–60 g of carbohydrates per hour [1].

For efforts lasting more than 2.5–3 hours, the guide allows up to 90 g of carbohydrates per hour using combinations of sugars you have practised with [1]. These are reference points to adapt, not mandatory targets for every runner.

A gel, a carbohydrate drink or solid food can each provide part of the same plan. Check the grams of carbohydrates per serving and add up what you take from all sources. Texture, eating pace and the water you take with a gel can affect tolerance.

If you prefer solid food, practise chewing and swallowing it while running. Your strategy needs to be repeatable at the aid stations available.

Why do digestive symptoms occur while running?

Digestive symptoms can include nausea, an urgent need to use the toilet or abdominal pain. Exercise, heat and food can all play a part. A consensus statement by sports dietitians recommends assessing the factors that trigger or worsen symptoms during exercise and adapting the strategy to each person [3].

Getting your digestive system used to eating during a race means practising over several sessions, starting with amounts you can tolerate; the guide says this practice may help, although responses vary between people [3]. Adjust one variable at a time: amount, frequency or format. If symptoms return with different products, we review the context before removing entire food groups.

Practise during training with what you plan to eat and drink in the race.

Why plan hydration for long races?

Hydration should be adapted to the heat, pace, sweat and available drink stations. The 2007 ACSM position stand recommends adapting fluid intake to individual losses. NATA warns that too much fluid, including some sports drinks, can cause exercise-associated hyponatraemia [4].

Practise how much you drink during comparable training sessions and avoid setting the same fixed volume for everyone. During prolonged events, sodium from food or drinks may be part of an individual plan, especially if you sweat a lot [4].

If you have a medical condition or take medication, agree on your strategy with your doctor. The sports drinks guide compares water with drinks containing carbohydrates and sodium.

How should you organise recovery after a marathon?

After crossing the finish line, aim for a recovery meal that includes carbohydrates, protein and fluid. For example, an omelette sandwich and fruit; later, rice with vegetables and fish. If you have another demanding session in a few hours, replenishing carbohydrates quickly becomes more important [1]. If you are going to rest, spread enough food across the day.

Recovery includes returning to normal eating when your appetite comes back. Digestive discomfort after running may make it easier to start with small portions of familiar foods. If you cannot keep fluids down, you need medical assessment. Also review rest and training load; food does not replace those adjustments.

What should women runners monitor regarding energy and iron?

Low energy availability can affect women and men. In women runners, changes in menstruation, stress fractures and persistent tiredness require clinical assessment [2]. Do not simply attribute them to hard training. We review food intake, training load and symptoms together with the medical team, without using weight as the only indicator.

For iron, the US NIH fact sheet sets an upper limit for total intake of 40 mg/day (40,000 µg/day) up to age 13. From age 14 onwards, including adulthood, the limit is 45 mg/day (45,000 µg/day) [5]. This includes food and supplements; it is not an amount you need to reach.

Blood tests and medical judgement determine whether there is a deficiency. Meat, seafood, pulses and other foods can provide iron [5].

What we see in consultations

In consultations, we often hear that people start planning their race fuelling when they pick up their race number. By then, no one knows whether the chosen gel sits well or how many carbohydrates the drink provides. We also see weeks of increasing training load with the same meals as on rest days. Before changing products, we write down the distances, schedules and what you already tolerate.

A useful strategy distinguishes between an easy training session, a long run and a race. With that record, we can make adjustments without turning every outing into an experiment. If you also cycle, the cycling guide offers another way to organise long rides.