How Your Nutrition Habits affect Your Runs

Let me tell you about my first half marathon. Bless my heart.

The race started at 8am. We drove two hours to get there that morning, which meant I was up before the sun and out the door fast. Breakfast was a coffee and a single pack of instant oatmeal eaten somewhere around 5:30am in the dark. I had a pack of gels with me because I'd heard that was a thing runners did. I felt prepared.

I did not use those gels until mile nine. By mile ten and a half I hit the wall so hard I didn't know what happened. My legs felt like lead. My heart rate wouldn't come down no matter how slow I went. Drinking water made me nauseous. My muscles started cramping one at a time, like they were taking turns giving up on me. The last mile of my first half marathon was a rotation of stop, stretch, shuffle, walk, stretch, repeat. It is probably the second worst I have ever felt in my entire life.

I crossed the finish line and called my coach.

The answer, it turned out, was breakfast. And the gels I waited until mile nine to use. And the two hours between eating and racing that I hadn't accounted for at all. My body ran out of fuel and then kept running anyway, pulling from reserves it didn't really have, until everything shut down at once.

Fast forward about six months. Second half marathon, Middle Tennessee, August. If you know, you know—it was brutally hot. Hotter than any of my training runs, hotter than I expected, hotter than I was ready for. This time I knew how to fuel. I knew how to hydrate. I did both. And I made it much further before I felt it coming.

But after the race—after the heat and the miles and the not-quite-enough of everything—the lead legs came back. The nausea came back. The "I hate everything about running and I am never doing this again" feeling came back with a vengeance.

Two different races. Two different problems. Same wall.

And both of them came down to the same thing: I hadn't fueled my body the way it needed to perform. Not before, not during, not enough.

What’s Happening in Your Body When You Run Under-Fueled

Running requires fuel. That sounds obvious, but most women don't realize how much fuel it actually requires—or how quickly the tank runs dry when you haven't eaten enough before you lace up.

Here's the short version: your body runs on glycogen, which is just stored glucose—the energy your muscles pull from when they're working hard. You build up glycogen stores by eating carbohydrates. When you run, you burn through those stores. When the stores run out, your body has to find another way to keep going—and that's when everything starts to fall apart.

Your legs feel heavy because your muscles are essentially running on empty. Your heart rate spikes and won't come down because your body is working harder to do the same amount of work with less available energy. You feel nauseous because your digestive system is competing with your muscles for whatever blood flow is left. You cramp because your electrolytes are depleted and your muscles are fatigued beyond what they had fuel to handle.

That wall I hit at mile ten and a half? That was my glycogen stores running out. My body had been sending signals for miles—slow down, something's wrong, I need fuel—and I hadn't been listening because I didn't know what I was hearing yet.

The good news is that this is almost entirely preventable. Not with complicated nutrition protocols or expensive supplements or perfect race-day planning. Just with food. The right food, at the right time, before you head out the door.

What To Eat Before A Run and When To Eat It

The timing matters almost as much as the food itself. This is the part nobody tells you when you first start running—you can eat the right things and still feel terrible if the timing is off. I learned this the hard way at 5:30am with my instant oatmeal and a prayer.

Here's a simple way to think about it:

If you have two or more hours before your run, you have time for a real meal. Something with carbohydrates for quick fuel, protein to support your muscles, and not too much fat or fiber—both of those slow digestion and can cause stomach issues mid-run. Think oatmeal with a scoop of protein powder. Eggs and toast. Greek yogurt with fruit and granola. A banana with peanut butter and a hard boiled egg on the side.

If you have thirty minutes to an hour, keep it small and simple. Your stomach doesn't have time to process much, and the last thing you want is to feel heavy and sluggish when you start moving. A banana. A piece of toast with a little peanut butter. A handful of crackers. Something easy, something fast, something your stomach knows how to handle.

If you're running first thing in the morning with almost no time before you head out—which I know is most of you—even something small is better than nothing. A few bites of a banana. A small handful of cereal. Half a granola bar. It won't fully stock your glycogen stores but it will tell your body that fuel is coming and take the edge off the first few miles.

And if you're going out for longer than an hour, you need to fuel during the run too. This is where gels, chews, or even real food like dates or banana pieces come in. Don't wait until mile nine like I did. Start fueling around the forty-five minute mark and keep going every thirty to forty-five minutes after that. By the time you feel like you need it, you're already behind.

Morning Anchors Matter Even More On Run Days

Remember Shift One from the Add, Don't Subtract guide—anchoring your morning with something that has protein before the day takes over? On run days, that shift becomes even more important.

Here's why: if you're running in the morning, your glycogen stores are already partially depleted from overnight. You've been fasting for seven or eight hours. Your blood sugar is low. Your body is already asking for fuel before you've even put your shoes on. Sending it out for a run in that state is like starting a road trip on an empty tank and hoping you find a gas station before things go wrong.

And if you're running later in the day—after work, during lunch, whenever you can fit it in—what you ate that morning still matters. A lot. The morning anchor sets the tone for your entire day of energy. Women who skip breakfast and run at 5pm are often running on a full day's worth of under-fueling, not just the hour before their workout. That's why the run feels so hard. It's not the run. It's everything that came before it.

I see this constantly with new runners. They think their fitness isn't there yet because their runs feel so difficult. And sometimes that's true—fitness takes time to build. But more often than I'd like to admit, the run feels hard because they haven't eaten enough. Full stop. We fix the fueling and suddenly the same route feels completely different. Same legs, same lungs, same pace. Just enough fuel this time.

Your fitness isn't always the variable. Your breakfast might be.

Food Isn’t Separate From Your Running. It’s Part of It.

I want to bring this back to where we started—me at mile ten and a half, legs like lead, wondering what was happening to my body. And then six months later in the August heat, same wall, different race, same root cause.

I wasn't undertrained. I wasn't too slow. I wasn't built wrong for this sport. I just hadn't learned yet that what I put in my body before I ran was going to determine almost everything about how that run felt.

That's the thing nobody tells you when you start running. You spend so much energy thinking about pace and distance and shoes and training plans—and all of that matters—but the variable that will change your runs faster than almost anything else is what you consume before, during and after the run.

Fueling well isn't juust for elite runners. Or fast runners. Or people who can run a certain distance. It's a human thing—whatever level you're at, whatever pace you're running, whether you're doing a 5K or a half marathon or just trying to make it through thirty minutes without stopping. Your body needs fuel to do the work. Give it fuel and it will show up for you. Don't, and it will remind you—usually about halfway through—that it had other plans.

Your legs are capable of more than you think. Feed them and find out.

-bk

If you want to start simple, grab my free guide Add, Don't Subtract here. The morning anchor shift alone will change how your runs feel. And if you're ready for a full four weeks of running and nutrition built around these exact principles, Run Ready has everything you need to get started here.