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5 Fueling Mistakes Marathon Runners Make

Updated: Mar 1, 2022

When you sign up for a marathon, it's not just the training you sign up for. Proper nutrition, hydration, sleep, stress management, and rest all play important roles in keeping a runner happy and healthy before making it to the race start line. As a Dietitian Nutritionist working with athletes to fuel their training, I see these common mistakes in newbie marathoners up to runners that have a couple races under their belt. Here are 5 fueling mistakes marathon runners make and how to avoid them.

Mistake #1: Dieting + Marathon Training

It’s tempting to use a marathon as a way to lose weight. However, this could very likely backfire. Marathon training involves logging high mileage and hitting the pavement/gym frequently. This takes a lot of energy from the body, and being in a calorie deficit could wreak havoc on training, health and well-being. It’s a common occurrence in marathoners attempting fad dieting/calorie deficits to find themselves later overeating/binging because of the body’s high demand for energy. This can cause a runner to end up gaining weight during their training cycle. Dieting will make workouts more difficult, will impair the ability to recover from those workouts, and increase risk of injury before a runner can even get to the start line.

These, among others, are reasons I discourage marathoners from fad dieting/focusing on weight loss while training for a marathon. There are so many other fantastic reasons to run a marathon! An adequate, frequent, and varied nutrition plan during marathon training is incredibly important for the aforementioned reasons. Avoiding this mistake will make a runner feel stronger at workouts, improve recovery, and decrease risk of injury.

This RDN recommends;
  • Prioritize at least 3 meals per day, no skipping meals.

  • Have snacks at the ready, perhaps at least 1-2 per day.

  • More often than not, have a source of carbohydrate, protein and fat at each meal.

Mistake #2: Not planning pre- and post-run fueling

I work with many runners that are busy. Full time employees, parents, students - you name it. Not only are they figuring out to incorporate their workouts (that can be up to 4 hours at a time), but they also have multiple other responsibilities in a day. Sometimes, proper fueling before and after workouts gets thrown out the window. I see scenarios like forgetting a snack/skipping a meal due to work, or a runner getting home after an evening workout with no plan for dinner.

Going too long between fueling up for a workout can cause runners to feel light-headed and extra fatigued at their workouts; making them fall short of their scheduled paces that day, or even having to cut their workout short. While this can happen during your training cycle, because we are all human and don’t have perfect days, it’s the consistent poor workouts that will limit your training.

I also see runners waiting too long to have their post-workout fuel due to forgetting, simply not planning, or because of a decreased appetite. Going too long without refueling after will not only make a runner feel ravenous, but will also limit proper recovery; poor muscle growth and adaptation, impaired glycogen (energy) storage, and prolonged inflammation. I also see this play out where runners will more often opt to go through the drive thru, order in, and/or overeating due to being so famished and fatigued.

This RDN recommends;
  • Have a meal/snack within 4 hours of a scheduled workout. If it’s 3-4 hours, a meal is a good choice. If it’s <2 hours, a snack is a good choice.

  • Have the post-workout fuel within an hour after a workout. If having a meal within an hour is not an option, have a snack that includes carbohydrate and protein.

  • Plan ahead & prioritize fueling like workouts. See this blog post for a list of easy grab’n’go snacks for runners.

  • Poor appetite is common after strenuous exercise, but does not mean the body doesn't need to refuel. Have an easier to digest snack, like; a smoothie, chocolate milk, or greek yogurt.

Mistake #3: Not eating enough carbohydrates

Everyone need carbohydrates! Runners have especially increased carbohydrate needs! Carbohydrates get a bad wrap in a culture today for a myriad of reasons. However, many of these claims are simply false or misguided, and can negatively impact a runner when they choose to restrict their carbohydrate intake.

Carbohydrates are our body’s most efficient source of fuel when compared to other nutrients like protein and fat. Carbohydrates are the exclusive fuel used for our brains and central nervous system. Carbohydrates benefit runners by providing more energy, more quickly for the body to use for workouts. Because of the amount of energy demanded by the body during marathon training, a runner will need to eat enough carbohydrates to keep up with what is expended. Research shows us that runners that eat plenty of carbohydrates see improved performance; they are stronger and faster.

Not eating enough carbohydrates can leave a runner feeling fatigued, light-headed, foggy, and irritable during workouts and throughout the day. Runners may also find themselves with increased cravings for refined carbohydrates, like; cookies, cakes, candy, muffins, etc. when not eating enough carbohydrates. Many athletes come to me saying they are “addicted to sugar!”, when in reality, their body’s are naturally responding to the lack of energy it desperately needs by increasing the desire for foods that will provide that quick energy.

When a runner incorporates adequate carbohydrate intake, particularly from whole grains and fruits, they have better energy for workouts and day to day responsibilities. They also avoid the constant, intense desires for foods like cakes, cookies, muffins, etc. These types of foods are absolutely fine to have! However, when they make up the majority of our diet, we are missing the opportunity for more nutrient-dense foods that will help marathon training and a runner's overall health.

This RDN recommends;
  • Have a source of carbohydrate at each meal and snack, such as; bread, cereal, fruit, potatoes, rice, pasta.

  • See if you can make at least half your intake of grains from whole grains, like; whole wheat bread, oatmeal, brown rice.

  • Don’t be afraid of fruit! Fruit’s natural sugar, fiber, and antioxidants are an excellent choice for runners to increase their carbohydrate intake.

Mistake #4: Forgetting to eat and drink during long runs

Have you ever experienced a “bonk” or “hitting the wall”? I know my clients have - and it is not a fun place to be! If you are unfamiliar with this term, bonking occurs when the body’s glycogen (energy) stores have depleted, and the body then begins to rely on solely fat for energy (a less efficient source of energy), causing the runner’s brain and body to essentially quit working.

Our body stores carbohydrates, glucose, as glycogen in the body. As we run, the body can pull from that energy storage. The problem is that the body has only so much glycogen it can actually store. Therefore, as a runner hits higher mileage, we need to “restock” this energy to avoid reaching a point of depletion or “bonking”. Here is a more in-depth Runner’s World article on the science of bonking.

In addition to using up glycogen stores, the body loses fluid through sweat during workouts. Like carbohydrates, fluids will need to be replaced once a runner is hitting higher mileage. See this post for more on hydration and fluid for a runner. Fluids also help the body absorb the highly concentrated carbohydrate fuel sources used on the run to replace lost energy stores.

The time to start implementing fuel and hydration occurs when training runs start to creep up to 75 minutes or longer. Focus on easy to digest carbohydrates, such as; gels, gummies, liquids, or fruit (whole and dried) as examples. Plan out how you will be able to drink water, whether that is by placing water stops along your route or bringing a portable fluid container with you. I highly recommend heading to your nearest local running store to purchase easy to pack and accessible options for both fuel and hydration to have on the run!

This RDN recommends;
  • Consume between 30-60 grams of easy to digest carbohydrate every hour of a training run that is 75 minutes or longer.*

  • Drink ~13-27 oz. fluid per hour on a long run, more may be needed in extreme temperatures or if you are a heaver sweater.*

*These are general recommendations, individual needs will vary, but this could be a good place to start.

Mistake #5: Relying too heavily on supplements; vitamins, minerals and protein powders.

Marathon training is intense. It pushes the body to the limit. It takes a lot of time and energy. It can be easy to take the “easy route” when it comes to nutrition. I find a lot of my clients and others in the running community turning to supplements for any number of reasons, but more often than not, it’s to “make up” for not eating enough vitamins and minerals in their diet, or they feel like they have to use protein powders to meet their needs or be healthy.

Supplements can absolutely be necessary, however, they shouldn't be used to substitute a varied and adequate diet. Think of supplements as the frosting on a cake - they can add some flare or really round out the overall product, but they are not the star of the show (in full transparency I do love frosting, but the cake is and always will be the star of the show!). Supplements are not regulated by the FDA, meaning what is said to be in the supplement, the amount it states it has, and the claims are not regulated. Check out this Instagram post for more on supplements.

Whole foods are going to give a runner the biggest bang for their buck when it comes to performance, recovery and health. This is especially true in marathon training when the body is being pushed to the limit.

This RDN recommends;
  • Before taking a supplement, consider if you can get the nutrients found in that supplement from food, and speak with your physician or registered dietitian nutritionist.

  • Use “processed” food to your advantage! Pre-cut, pre-sliced, frozen, canned fruits and vegetables can be just as nutritious as fresh options. Low on vitamins, minerals and time? Use these quicker cooking/prepared options to get in those valuable nutrients! Check out this post for my top quick cooking pantry staples.

  • Reserve protein powders for times when getting adequate protein from whole foods is impractical or impossible. Otherwise, focus on getting your protein from whole foods!


Are you training for a race and are interested in one on one nutrition coaching to fuel better and decrease risk of injury? Click here to learn more about working with Maddi.

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