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A nutritionist’s guide to marathon training

What to eat when training for a marathon

Jo Scott-Dagleish

Endurance Sports Nutritionist

A marathon runner eating a healthy lunch

How do you successfully fuel yourself to run a marathon? Jo Scott-Dalgleish, a BANT-registered nutritionist who specialises in dietary support for endurance athletes, offers her advice on what to eat while training.

When it comes to training for a marathon, what you eat is key. Yet with time tight, lots of runners don’t focus enough on their nutrition, which may contribute to injuries, abandoned runs and hitting the dreaded wall. Jo Scott-Dalgleish, a nutrition practitioner who works with long-distance runners, cyclists and triathletes, believes that success comes down to planning. "To perform well you need to think about what you are eating, how much and when," she says. "The mistake I often see people make is finishing a run hungry and grabbing something, anything, from the fridge, which might not be what your body needs. Nutrition is too important to leave to chance."

Here’s Scott-Dalgleish’s guide to getting your diet marathon-ready.


The primary source of energy for runners is carbohydrates, but as Scott-Dalgleish points out, not all carbs are created equal. “During the training period it's not about having lots of extra sweets or honey,” she says. “This is the time to focus on whole grains. So whole wheat bread, porridge oats, whole grain rice… Think brown foods, which will produce a steady supply of energy.” Scott-Dalgleish’s recipe for a successful long run is a breakfast of porridge oats with some dried fruit, banana or a teaspoon of honey. “The whole grain foods are for steady energy and the little bit of sugar tops it up”. Scott-Dalgleish recommends eating more carbohydrates on days when you run than on rest days.


Every run does microscopic damage to your muscles, which your body repairs, with the muscles coming back even stronger. Proteins aid this process, so Scott-Dalgleish recommends incorporating more into your training diet, ideally within an hour of completing a run. "Meat, fish, yoghurt, milk, cheese and eggs are all good sources of protein," she says. “Alternatively, if you’re on a plant-based diet, look at nuts, beans, quinoa and soya yoghurt.”


Scott-Dalgleish recommends having plenty of good quality fats as part of your diet. She particularly rates olive oil, oily fish like salmon, and dairy products such as yoghurt, cheese and eggs – or avocado, nuts and seeds if you are plant-based. "I'm not promoting good quality fats to help you run, I'm doing it to help you stay healthy," she says. "Fats are important for maintaining healthy hormone levels, for immunity so that you're less prone to colds and coughs, and as anti-inflammatories, which can help you avoid injuries while training."

When to eat

One of the mistakes Scott-Dalgleish often sees marathon runners make is to not increase their food intake in line with their training runs. “Marathon training usually takes place over 12 to 16 weeks,” she says. “Over that period you are going to gradually increase the amount of time you spend running, and if you do not increase the amount of food that you eat as well, you run the risk of underperforming, becoming demotivated or, if you significantly under-eat, getting injured.” Runners should build up their food intake gradually alongside their mileage. “What you shouldn’t do is jump in and say, 'Oh, I'm now training for a marathon' and suddenly start eating an extra 500 calories a day. It's about matching your energy intake with your energy expenditure.”

It's also important for runners to think about when they eat as well as what they eat. If you are a morning runner, Scott-Dalgleish believes it is fine to do short runs before breakfast, but you should have some starchy foods in your evening meal the night before. "Brown rice or sweet potato are good options," she says. "They will give you some carbohydrates to run in the morning." If you run on empty, then Scott-Dalgleish says that within an hour of finishing you should take in some protein and carbohydrates, perhaps a breakfast of yoghurt and muesli.

If you’re running after work, Scott-Dalgleish thinks it’s important to eat something before you set off. "There's too long a gap between lunch and a 6pm run,” she says. “I’d go for a whole grain chicken sandwich and a piece of fruit at lunch and then about an hour before your run, something that offers quick energy like raisins, a banana or a rice cake."

Building up to the big day

As you build up the length of your runs, Scott-Dalgleish says you should think about fuelling yourself on the go. "Once you're doing more than about 75 minutes of running, you need to start taking on some carbohydrates during your run, so you can keep going," she says. "Your body can only store limited amounts. 'Hitting the wall' happens when you haven't fuelled yourself while running and eventually you just run out of gas." Many turn to glucose drinks or energy gels, and while Scott-Dalgleish agrees that they can be useful, she advises experimenting with these well in advance of marathon day. "Sports drinks or gels can disagree with your stomach," she says. "You don’t want to discover this on the day of the marathon – it is not going to make for a happy day out!"

Ultimately, Scott-Dalgleish believes that, like any healthy diet, a successful training diet is about balance. "It takes a lot of effort to train for a marathon and nutrition is an important part of that training," she says. "It's vital that you eat good quality foods that provide various nutrients and not rely on highly processed foods. It's not just about calories, it's about quality foods that are going to help you get ready to run the distance."

You can read more of Jo Scott-Dalgleish's nutritional advice for marathon runners on her blog,

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