Imagine you’re in the midst of your long run, feeling completely invincible, when out of nowhere, your legs start to feel like lead, you’re exhausted and lightheaded, and you just can’t keep going. It’s safe to say that most of us have experienced this nightmare scenario of “hitting the wall” or “bonking” before.

Bonking occurs when your body runs out of glycogen (stored carbohydrates), its primary fuel source, explains Amy Stephens, RDN, CSSD, a licensed dietitian who specialises in sports nutrition. When these reserves deplete, your muscles have to rely on fat for energy instead, she says, which burns much more slowly, causing sudden and intense fatigue.

“Your body can only hold about 90 minutes of fuel for running,” Stephens says. “Once that glycogen is used up, your body needs to slow down.”

If you keep hitting the wall, it’s a major sign your overall nutrition strategy requires some serious readjustment…

If you keep hitting the wall during your long runs, it’s a major sign your overall nutrition strategy requires some serious readjustment, since fuelling properly ensures you avoid the dreaded bonk. Luckily, some easy signs tell you when it’s time to make a change to your fuelling routine. Follow this guide to improve not only your nutrition, but your overall training.

Signs Your Nutrition Plan Isn’t Working for You
If you relate to any of the following experiences when training, you may be underfuelling.

1. You’re Constantly Thinking About Food
One major tell you aren’t fuelling correctly (read: enough) is that you’re feeling unusually hungry and thinking about food way more than you’re feeling unusually hungry and thinking about food way more than you typically do, especially leading up to a long run, according to Tara Collingwood, RDN, CSSD, a board-certified sports dietitian. You might also crave sugar when you don’t usually, she says.

If this happens, your body is signalling that your glycogen stores are low and need to be replenished, she explains. As a training runner, it’s important to incorporate enough carbs into your meals every day so you can deepen your glycogen stores and have enough fuel come race day, Stephens adds.

What does “enough carbs” look like? On an easy day where you’re exercising for an hour or less, one-third of your plate should be filled with carbs, according to Stephens. On a harder day where you’re exercising for more than an hour, half of your plate should be filled with carbs.

2. Your Mood Is Taking a Turn for the Worse
Irritability, brain fog, low motivation, and feeling unusually emotional can be signs of inadequate fueling, according to Collingwood. “The brain depends heavily on glucose, so when energy availability drops, mood and focus can suffer,” she says.

Constant underfueling can even put you at risk for developing depression or anxiety, according to a 2023 study published in the Clinical Journal of Sports Medicine. Researchers found that many women with low energy availability (when your calorie intake isn’t enough to cover the amount of energy you need to support your daily life and training) also had moderate to severe symptoms of anxiety and depression.

3. Your Runs Feel Unnecessarily Hard
Feeling heavy legs, sluggish early in a run, or unusually fatigued despite good training are also red flags your nutrition plan isn’t working for you, according to Collingwood. “Many runners assume they just need more fitness, when in reality they may need more carbohydrates and overall calories,” she says.

4. You’re Not Recovering Well From Your Workouts
Does your entire body feel heavy and sore, like you’re dragging around a ton of bricks, in the days after a run? This is yet another telltale sign you’re fuelling incorrectly, according to Katie Whitson, RDN, registered dietitian nutritionist at Health Loft.

“Noticing poor recovery from your runs indicates insufficient protein and carbohydrate intake for recovery,” she says. “It’s important to note how you feel while running and how you recover from your runs throughout your training process to ensure you are fuelling adequately with enough carbohydrate and protein.”

If you’re not eating enough to offset your training, you may also be more susceptible to recurring injuries, especially bone stress injuries.

How to Fuel for a Long Run the Right Way
Now that you know what’s not working, here’s what will, according to our experts.

“To prevent hitting the wall, runners should focus on consistent carbohydrate intake throughout the day rather than trying to ‘rescue’ themselves right before a run,” Collingwood says.

Here’s exactly how to fuel before, during, and after a long run to perform and feel your best.

Before a Run
A good rule of thumb is to avoid starting a long run hungry, according to Collingwood. Prioritise a high-carb, easy-to-digest meal between one and four hours before your long run, Whitson adds. (Avoid fat and fibre to reduce GI distress.) This meal should contain 1 to 4 grams of carbs per kilogram of bodyweight, according to Whitson.

Collingwood recommends eating oatmeal with banana (or fruit of choice) and honey or toast/bagel/waffle/English muffin with peanut butter or jam and some fruit.

“Hydration matters, too,” Collingwood says. “Starting even mildly dehydrated can worsen fatigue and increase perceived effort. If you are a heavy or salty sweater, you can start with electrolyte drinks before your run to get some extra sodium on board.”

During a Run
In order to maintain blood sugar levels and prevent fatigue during a long run, you want to consume 60 to 90 grams of carbs per hour, which is around two to three gels depending on the brand, according to Stephens. You can also get your fuel from chews, sugary candies (like jelly babies/beans), dried fruit, or sports drinks, Whitson and Collingwood add.

After a Run
Consuming carbohydrates plus protein within about 30 to 60 minutes after a long run helps replenish glycogen stores and supports muscle repair, according to Collingwood. “Underfuelling after long runs can create a cycle of poor recovery that impacts the next several workouts,” she says.

She recommends getting about 1 to 1.2 grams of carbs per kilogram of bodyweight and 0.2 to 0.3 grams of protein per kilogram of bodyweight within an hour of your long run. A simple recovery meal might include chocolate milk, yoghurt with fruit and granola, or a protein smoothie.

Follow that with a full meal within two hours of your long run, Collingwood says. This might be a lean protein with rice or a turkey wrap with veggies and fries, Whitson adds.

This article first appeared on the Runner’s World USA website.

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