If you, like many runners, have ever slogged through what you thought would be an easy jog, or completely bonked during a marathon for which you had trained properly, then you have probably asked yourself, “what went wrong?” Often, the problem isn’t in your kilometres, but your fueling, which is one of the key aspects of any runner’s workout and racing plan.

Fueling is highly personal, but nutritional guidelines can help you find what works for you. Choosing the right foods to eat and when is as important as wearing the right running shoes, drinking water, and knowing how far and where you plan to run. “If you are experiencing chronic fatigue, lack of focus, or persistent headaches it might be a sign that you need to change your fueling,” Ellen Davis, a sports dietitian with The Performance Collective tells Runner’s World.

Here are three common pre-run fueling problems that runners face and how to avoid them.

A number of things seem to contribute to hitting the wall, according to a large-scale data analysis of recreational marathon runners, published in PLOS One in 2021. The researchers define hitting the wall as running out of glycogen, which is often due to poor race nutrition, as the researchers note. This is why they say in-race fueling is crucial for maintaining energy stores and avoiding an energy crash, particularly in marathons. (Steady pacing is another way to avoid bonking, according to the study.)

When fueled properly, your body stores about 90 minutes worth of glucose, Dr Carl Paige, chief medical officer and cofounder of the Medical Transformation Center explains to Runner’s World. Glucose is the sugar used for energy in your bloodstream, and after that, your body turns to glycogen, a source of energy stored in your muscles and liver.

If you’re eating three meals a day, plus a couple of snacks, it’s unlikely you will feel fatigued during a very short run, unless you haven’t eaten within the last couple of hours, but if you don’t fuel properly for longer runs, you may not be able to perform at your optimal level.

You also need to make sure the fuel for efforts lasting longer than an hour is the type of energy that your body can burn steadily, and you need to replenish that fuel as you clock more kilometres.

The Fueling Solution: Choose the Right Carbs at the Right Time
The glycemic index (GI) is a rating system from 0 to 100 for foods that are made up of mostly carbohydrates. For example, the glycemic number of white bread is 71, while meat, poultry and fish do not rank on the GI scale because they do not contain carbohydrates.

The GI number measures how quickly a food will cause a person’s blood sugar (glucose) level to rise. Lower numbers mean a food takes longer to change your blood sugar, while higher numbers change your blood sugar rapidly.

According to a few studies (most of which involve a small number of participants), it’s often best to eat foods on the lower end of the scale, because low-glycemic food offers more sustained energy — important for endurance athletes. Options for low-GI foods include rolled oats and brown rice.

Also, a pre-run meal should contain a balance of macronutrients, including protein and healthy fats, as well as complex carbs (those lower on the GI scale). But if you’re having a smaller pre-run snack closer to the start of your run, then you’ll want to focus primarily on carbs, Katelyn Greenleaf, a dietitian explains to Runner’s World. For that, Greenleaf suggests a handful of dried fruit, a few bites of a granola bar, or even just a few sips of a sports drink (all of which are higher on the GI scale).

“Simple carbs will provide an increase in blood glucose without feeling like your food is jumbling around in your stomach. Protein, fibre and fat can linger in digestion, therefore leading someone to feel like they ate too much before their workout,” Greenleaf says.

Also, avoiding bonking involves refuelling in the middle of a long run. The typical recommendation is 30 to 90 grams of carbs every hour.

The Problem: You’re Too Tired to Run
What if you can’t even find the energy to get off the couch and jog around your neighbourhood? Aside from noticing how you feel on a run, athletes also need to pay attention to how they feel throughout the day to determine if they need a change in fueling. You can’t expect to push yourself through a training run if you’re tired before you even begin.

If something feels off in your “recovery, sleep, mood, and focus,” says Davis, then it may be a sign that your daily nutrition plan is probably off. If you’re getting through your days and your runs without fatigue, headaches, or irritability, it’s likely your diet is working.

The Fueling Solution: Eat Consistently
The body’s process of turning food into energy is called metabolism. Your metabolism, Davis explains, produces energy for bodily functions including breathing, digestion, muscle contraction and relaxation, cellular growth and repair. Inadequate caloric intake may affect your ability to carry out these functions efficiently.

Most of us assume that our bodies use hunger to tell us when to eat, but being an avid runner can confuse those signals. Studies have shown that exercise suppresses appetite signals, so a highly-active person may miss some of their body’s calls for fuel.

Not relying on your fitness trackers to see how many calories you burn every day is also important, because those are only estimations, Davis says. “Take those numbers with a grain of salt,” she adds.

Davis reminds her runners that they need to fuel for both their life and their runs. “I tell my clients to practice frequent fueling,” Davis says. Three meals, plus snacks, during the day will typically help you meet your nutrition and calorie needs.

Also, while you may be getting the right amount of food, certain health issues may keep you from absorbing the nutrients. “Allergies or food intolerances can also make you feel tired, despite having eaten in that Goldilocks ‘just right’ zone,” Paige says.

If you notice you feel super fatigued, despite potentially eating more, it might be time to consult with your doctor to see if you have any underlying issues.

The Problem: You Slog Through Runs
Training involves all types of runs — intervals, tempos, long runs, easy days — and at least in the beginning of a workout, you should feel energetic. However, if you feel sluggish and like you’re dragging your feet when you start running, it could be a sign that you need to fuel differently — in this case, maybe you need to eat a smaller meal or snack before hitting the road or give yourself more digestion time.

“If someone is feeling lethargic, heavy, weighed down or slothful, this could be due to eating too much before exercise,” says Greenleaf. This may also cause some digestive discomfort.

The Fueling Solution: Shorten Your Run or Take Time to Digest
Consider cutting your workout a little short if you’ve eaten a large meal, especially a big meal close to when you started running.

It’s a good idea to plan your meals so that you have more time to digest before hitting the road, says Davis. Remember, your body uses energy to digest a meal, and asking it to perform intense exercise while it’s digesting is asking a lot of your body — and it’s a request that can lead to an upset stomach.

While what works for you in terms of a pre-run meal or snack and when to eat it will be personal, if you’re looking for a general rule of thumb, go for a meal with a little protein, a little fat and a lot of carbs, Dr Pam Bede, author of Fuel the Fire, told Runner’s World in a previous article on over-fueling. Aim for 1 gram of carb per 500g of body weight and wait about two to three hours before running if you have this full meal.

You can get away with less digestion time if you have a smaller snack, made up of mostly simple carbs, as Greenleaf suggested.

The key with both options is to try out different foods at different times and see what works best for you.

The Bottom Line on Pre-run Fueling to Maintain Your Energy
Nutrition for daily fuel and nutrition for training is very individualised, so following a friend’s plan or even a plan laid out in a training plan may or may not work for you. “The true value of eating lies in finding the approach that works well for you and helps you stay on the road or the trails,” says Davis.

To that end, save some time after a training session to reflect on whether your fueling routine worked well. Make connections between what you ate and how you performed. Then, says Davis, stick to that strategy that works for you while continuing to monitor your body’s feedback, in the form of performance and recovery.

Finally, don’t forget to refuel after your run to prevent ravenous eating later in the day or night, says Davis. Refuelling should include a combination of complex carbs, protein, and fat to keep your energy up and your hunger at bay.

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