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ISSA, International Sports Sciences Association, Certified Personal Trainer, Nutrition, Marathon, Nutrition for a Marathon Runner: Before, During, and After

Nutrition for a Marathon Runner: Before, During, and After

Reading Time: 6 minutes 6 seconds


DATE: 2020-09-02

Marathon training and running a marathon is nothing less than a feat of both mental and physical strength, endurance, and stamina. The 26.2-mile run isn't something you just wake up one morning and decide to try. Becoming a marathoner takes time, dedication, and preparation. Proper physical preparation is important when training for a marathon. But equally important is having a proper nutrition plan.

Nutrition for Endurance Runners

Food is more than simple nutrition. Food is fuel. Nutritional needs look different during the weeks of preparation leading up to the event, race week, the day of the event, and even during the event itself.

Physical preparation for running a marathon starts weeks, even months, in advance of the actual event. Nutritional preparation similarly needs to start weeks before the event itself. This time leading up to the event allows you to fuel your body so it can meet the physical demands being placed upon it.

Additionally, this window of time provides the space to figure out what nutrition works best for you. This includes not only foods and food products consumed, but timing as well.

Pre-Run Nutrition

Carbohydrates are probably the single most important nutrient in a marathon training diet. Endurance runners need about 7-10 grams of carbohydrates per kilogram of body weight during training. Runners should be closer to the upper end of this range as they get into longer runs. For a distance runner, about 55% of daily calories should be from carbohydrate sources during training and close to an upwards of 65% before a long duration event like a marathon. High amounts of carbohydrates ensure saturation of the glycogen stores within skeletal muscles. Glycogen is the storage form of carbohydrates and is used to fuel the body during exercise.

Fueling up before a long-duration event is critical. Encourage your clients to experiment with various types of foods before they plan to exercise. This will help determine what works best and feels best for their body. Try eating something high in carbohydrates that is relatively easy to digest. Digestion during exercise is challenging. The body is diverting blood to the working muscles and not really focusing much on digestion. To help with this, encourage your clients to avoid processed foods and foods that are high in fat and protein. These macronutrients will slow down the digestion process. Stick to easily digestible carbohydrates to keep digestion calm while running.

Mid-Run Nutrition

If your clients are interested in training for a marathon, they need to get comfortable fueling during their runs. Their body must learn to accept food during training runs. This may be one of the biggest challenges that endurance runners face. Yet, for continuous endurance exercise that lasts more than 45, fueling during exercise is a must.

In order to run 26.2 miles, your body will need some refueling during that time. A helpful tip to remember is to fuel early and often. It is critical to build this into your client's training routine in the weeks and months leading up to the race. It is better to fuel early before you feel you really need it than to wait until you hit a slump and be waiting on that energy to come.

Think of it like taking Tylenol for a headache. It's best to take the Tylenol when you feel a headache coming on. You don't wait for the headache to arrive and then take the Tylenol, waiting 30 minutes for it to kick in. You take it early so that by the time you need it, it's already started working. It is important to stay ahead of feelings of exhaustion rather than trying to fight them when they are in full swing. Keep topping up the tank even if you think you don't need it. You do. And your body will thank you for it later.

Smaller snacks are best during a run as they are more easily digested and still fill up muscle glycogen and provide a boost of energy. Try to find something that provides easy to digest carbs like dried fruit or an energy gel. Experimenting during training will help your clients discover which foods work best for them while running. Runners should aim for 30-60 grams of carbohydrate intake per hour during their run. Experiment with using sports drinks, energy gels, chews, and bars. It depends on runner preference here and what you feel works best for your body. At the end of the day, it's about healthy eating and finding the right fuel to power your game plan.

Post-Run Nutrition

Focusing on pre-race nutrition as well as race day nutrition is critical for overall performance. But just as important, is fueling after completing a run. Try to consume a recovery snack of protein and carbs 30-45 minutes after a run. This is a very important window when your body is very responsive to nutrition and will utilize nutrients to rebuild and repair muscles.

Post-race nutrition is where protein intake becomes a bigger focus. Protein provides an edible upgrade for your legs and leg muscles. It helps the body build new muscle and recover quickly while also avoiding injury. Encourage your clients to find healthy protein sources whether animal or plant-based. Chicken is a great animal-based lean protein. It provides selenium which helps protect muscles against free-radical damage during exercise, and niacin which helps regulate fat burning while running. Protein will also help to stabilize blood sugars and keep you feeling fuller longer.


Hydration is a key factor to consider when training and running a marathon. It's important to hydrate before, during, and after a long run. Fluids help to regulate body temperature, flush out waste, and ensure joints are healthy and lubricated. This is extremely important if you're going to be putting some miles on those legs.

Fluid intake must match fluid loss when running for endurance training. Hydration balance is a key component to performing well on long-distance runs. Too little fluid intake can lead to hypernatremia. This results in the sodium levels in the blood becoming too concentrated. Likewise, too much water can result in hyponatremia which dilutes sodium levels in the blood.

Understanding your sweat rate can help you prepare and understand your hydration needs while training. Sweat rate can be determined by tracking weight loss during a training run. Weigh yourself before and after a run to see how much fluids you lose during your training sessions. You can calculate your sweat rate by subtracting post-run weight from the pre-run weight and adding the volume of fluids consumed during your run. Try out this sweat rate calculator to determine your client's individual sweat rate. If your clients are training at a similar pace to their actual marathon race day pace, then their sweat rate should hold fairly similar. To prevent dehydration, you should drink amounts similar to your sweat rate.

Some runners may choose to consume a sports drink with electrolytes during their runs. Electrolytes are minerals such as sodium, potassium, chloride, and bicarbonate, which help to regulate nerve and muscle function. They also help in maintaining pH and water balance within the body. One thing to note is that large amounts of sodium are not typically lost during a marathon so be cautious of overdoing it as it may lead to hypernatremia.

Another addition some runners choose is caffeine. Some athletes choose caffeine before or during a race to boost their overall performance. This depends on individual differences in tolerance as well as perception. Only small amounts of caffeine are needed to provide optimal effects. The general recommendation is not to exceed a daily intake of 400mg of caffeine.

Nutrition Plan

Following a few simple rules will help you have a successful running experience all the way from the start of your training to that oh-so-sweet finish line.

Preparation is key. Experimenting and finding which foods provide adequate energy for your runs and when to consume those foods is critical. This varies from person to person, so capitalize on those weeks of training leading up to the event to determine what works best for you. When race day comes, stick to the game plan you have developed and try not to stray off course. Race day is not the time to be experimenting with new foods. Stick to what you know.

Increase carbohydrate intake in the days leading up to the event. This means eating more carbohydrate-rich foods, not just more food. Be smart about the foods you choose. Nutritional choices have an impact on your race time of course. But they also influence your energy levels, avoiding dehydration, and optimizing your recovery.

Fuel early and hydrate often. Don't wait until you feel like you need it. Beat those needs to the punch and stay ahead of fatigue and exhaustion. Stick to your game plan and enjoy your achievement. And don't be afraid to indulge a little after those 26.2 miles. You've earned it!

Add another tool to your personal training toolbox with ISSA's Nutrition course. You'll learn how to successfully leverage food and it's nutrients to help your clients hit their goals in no time!

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ISSA | Nutritionist

By becoming an ISSA Nutritionist, you'll learn the foundations of how food fuels the body, plus step by step methods for implementing a healthy eating plan into clients' lifestyles.

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