Marathon Training

The Diet

Running a marathon is no mean feat, so before we begin, hat tip to you for taking the plunge.

The chances are you have a well structured, periodised and planned training programme to follow to prepare yourself for the marathon. But perhaps you are still wondering how to adjust your diet to best fuel and prepare yourself?

Alongside training, nutrition is equally important in your preparation, getting it right can certainly improve your performance and make the experience more enjoyable. On the other hand getting it wrong can leave you struggling and in a world of pain. In the following two part series we will cover exactly what you will need to do to adjust your diet in training for and then in the days leading up to the marathon.


The first and most fundamental adjustment you need to make to your diet when commencing marathon training is simply increasing your daily energy intake. The energy cost of running a marathon has been estimated to be between 2200 - 3200 kcal, while energy expenditure of training could be anywhere between 500 - 800 kcal per hour.

If you were to maintain your normal diet, with no adjustments the chances are you would create a negative energy balance, which will not only mean you lose weight, but will also reduce the amount of energy available to your body to support performance and recovery. Low energy intake for extended periods of time can also impact the immune system, making you more susceptible to picking up frustrating illnesses, not what you need when trying to prepare for a marathon.


Carbohydrate is used as a fuel for intense actions such as running, jumping and changing direction at speed. Carbohydrate is stored in small quantities as glycogen in both the muscle and liver, the best way to imagine this is whenever you eat a carbohydrate rich food the likelihood is that it will be used to top up small petrol tanks in your muscle and liver. Those petrol tanks are fuel reserves for intense activity.

Given that running is relatively intense, most of the energy you burn during your training runs will come from carbohydrate. So when increasing serving sizes at meals, it will be the carbohydrate component that needs to be adjusted the most, to top up those tanks and ensure they are suitably full for future sessions.

If we assume that you currently consume 2000 - 2500 kcal each day, you will likely need to add an additional 500 kcal of carbohydrate to your daily diet to meet the demands of daily training. That’s the equivalent of an additional banana and tablespoon of honey in your morning porridge, with a bottle of apple juice, a slightly larger serving of rice with your evening meal and three caramel rice cakes before you train.

Consuming between 5 - 7 grams of carbohydrate per kilogram of body weight should be sufficient to maintain the fuel tanks and support your performance and recovery. That is between 350 - 490 grams of carbohydrate for a 70 kg runner. Some recommended carbohydrate-rich fuel foods include oats, bran flakes, wholegrain bread, pasta, rice, cous cous, quinoa, potatoes, rice cakes, granola or cereal bars, fruits and fruit juices.

Carbohydrates can be categorized based on how quickly they deliver fuel to the body, this is often referred to as the glycemic index. High glycemic index foods such as white bread, white spaghetti, mashed potatoes, sports drinks, energy gels and candy deliver fuel rapidly and can be referred to as fast fuels. These foods, snacks or drinks are ideal before, during and after training and races, when the body needs fuel fast. Slow fuels are generally wholegrains such as wholemeal breads, pasta, bran flakes, wholegrain rice, quinoa, chickpeas, lentils and high fibre fruits such as apples. They deliver fuel slowly, over an extended period and should be prioritized at all other meals and snacks.  


Protein rich foods are digested, absorbed and broken down into individual amino acids which are primarily used to support growth and repair processes in the body, particularly in muscles. Imagine amino acids are like small bricks, these bricks are used to rebuild tissues. Running is incredibly taxing on muscles and joints, so consuming protein in sufficient amounts and at regular periods across the day is important to aid growth and repair processes.

Consuming around 1.6 grams of protein per kilogram of body weight should be sufficient to optimise the rebuilding processes, splitting this total daily dose into 4 or 5 equal parts will also ensure that the body receives a steady supply of building blocks throughout the day. That is roughly 112 grams of protein for a 70 kg runner, and 28 grams of protein per meal.

Suitable protein sources to aid repair processes include lean meats such as chicken, turkey and lean beef, eggs, fish, dairy products such as milk and Greek yogurt,soy, beans and pulses, and even whey or vegan protein powder if you struggle to meet the daily requirements from wholefoods.

Salmon, mackerel and sardines are particularly worthy of mention as they not only provide quality protein, but they are also rich in omega-3 polyunsaturated fats which are known to reduce inflammation, muscle damage and soreness. A very nice addition to the daily diet during intense training.


Fruit, vegetables and healthy sources of fat could easily be referred to as boost foods as they have the ability to boost numerous aspects of our health and functioning as humans, thanks to their vast quantities of vitamins, minerals, fibre, fatty acids, water and other phytonutrients.

Dietary nitrates have received serious attention in the sports nutrition space in recent years, owing to their ability to boost nitric oxide production, widen blood vessels, reduce blood pressure, improve blood flow, endurance performance and power output. The perfect storm for a runner in marathon training.

When selecting which vegetable to add to your meal, nitrate-rich vegetables such as beetroot, spinach, rocket, swiss chard and lettuce are certainly worthy of consideration. Current research suggests a dosage of around 800 mg may be required to boost performance in endurance events, with 100 grams of beetroot and spinach providing roughly 300 and 240 mg respectively. Including a variety of nitrate-rich vegetables each day, with each meal is a worthy consideration. Interestingly Power Beets contains 105 mg of nitrates per bottle, certainly a valued addition to your daily training diet.

Including a wide variety of fresh fruits into your diet is also likely to help your performance and recovery during this intensified period of training. We have known that fruit offers a host of health benefits for many years, but in recent times we have developed a detailed understanding of how fruit-derived polyphenols can benefit the body. Polyphenols have antioxidant and anti-inflammatory properties, which support the body, brain, heart and muscles train, compete and then recover. Current evidence suggests that doses of between 300 - 1000 mg per day maybe optimal. Interestingly cloves, peppermint, cocoa, dark chocolate, coffee, berries, cherries, pomegranate, beans, green tea and red wine are all rich in polyphenols and should feature in your training diet.


The human body is around 60% and you can lose anywhere between 500 ml and 3 litres of fluid per hour through sweat during intense marathon training. Consuming sufficient fluid each day to maintain hydration status is important. Dehydration impacts the brain, cardiovascular system and muscle strength and power. A tell tale sign of dehydration is lethargy and general fatigue, this can make daily life more difficult, nevermind your training. Drinking 1 ml per kcal consumed is a good general guide, so that could be anywhere from 2000 - 3000 ml per day and then an additional 500 - 1000 ml per hour of training.

The best way to monitor your hydration status is checking the colour of your urine. This certainly makes the next trip to the loo a little more interesting. Urine should be a pale, almost clear colour. The darker the urine the more dehydrated you are. Note that urine colour can be influenced by a variety of factors, including some vitamin supplements and beetroot juice, and other things, but as a proxy measure it is useful.

Individual sweat rates can vary considerably too and when body mass loss exceeds 2% your performance can suffer, so it maybe worthwhile assessing how much fluid you lose via sweat during your training sessions. Simply weigh yourself before you train and then again after, in the same clothing, ideally just boxer shorts. Any difference in body weight is assumed to be fluid losses through sweat, with 1 kg assumed to be the equivalent of 1 L of fluid. As an example, if I start my run weighing 70 kg and finish weighing 69 kg, that is 1 kg loss or 1 L of fluid lost through sweat. This is only 1.4% of my body mass, so is not going to hurt my performance, but I would need to consume around 1.5 L in the coming hours to fully rehydrate post-run.


Finding the motivation to get up and go, especially when it’s cold, wet and windy outside is challenge in itself. So adding in foods and fluids that can help get you amped up, ready and raring to go is most certainly worthwhile. Caffeine and caffeinated beverages such as coffee and the B.Fresh Focus shot can do just that. Caffeine is an adenosine antagonist, which in simple terms means it blocks the actions of adenosine and has a stimulant effect on the brain, improving attention, focus and generally get you more up for a long-grueling run. Interestingly caffeine can also reduce perceived exertion, making tough training feel easier and more enjoyable and it can also boost endurance so you can run faster. Quite literally the perfect addition to your daily training diet!

Be mindful that the stimulant effects of caffeine last for many hours, so drinking caffeinated drinks after 3 PM can interfere with your sleep, not such a good idea. So it’s best to consume these drinks earlier in the day and ideally around 30-minutes before you train.

Your Daily Diet

To conclude, you will need to increase your energy intake in training for the marathon, this can be achieved by adding more carbohydrate rich fuel foods into your normal diet. We have mapped out a recommended daily diet for an average 70 kg male in this document here, this can be used as a rough guide. Eating protein rich build foods at regular intervals throughout the day, with omega-3 rich options such as salmon multiple times per week, combined with some polyphenol rich fruits can help support recovery and optimise repair processes so you are less sore. Selecting nitrate rich vegetables such as beetroot and spinach, and including Perform into your diet are valued considerations too. Finally, a focus on maintaining hydration with sufficient fluid and timing caffeine intake to boost your mental and physical performance is essential.

Enjoy the struggle, training is hard but achieving a goal is incredibly rewarding. Keep going and we hope that these small diet tweaks can help make the process a little more enjoyable for you.

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