5 Foods You Should Really Avoid Before Working Out

Unless you’re into nausea, heartburn, and sudden poops.

August 14, 2024

If you’ve ever snacked on leftover pizza right before going on a jog or starting your Pilates class, then you’re probably well aware that what you eat can significantly influence your workout.

Foods affect your body in all kinds of ways, and that’s especially true when it’s on the move. “Some support your athletic performance, and some don’t help it at all,” Julia Long, RDN, LD, a performance dietitian with RC13 Sports, tells SELF. Sure, your body will get through exercise even if you just threw back a few handfuls of movie theater popcorn as you were lacing up, but the big question is: At what cost? Some foods can upset your stomach or make you feel sleepy, Long says, whereas others make you feel strong and energized.

Now, this doesn’t mean that any of these foods are “bad”—there’s a place for all of them in your diet if you enjoy them! It’s just that eating them right before your workout might not do you any favors.

So if you tend to reach for whatever’s in your snack cabinet only to feel nauseous 15 minutes into your cycling class (just me?), this guide is for you. We asked two sports dietitians who train professional athletes about the foods they recommend steering clear of about an hour before exercising. Here’s what they said.

Protein shakes

Lots of folks grab a protein shake before a workout—they’ll help your muscle grow and recover faster, right?—but it’s actually not doing you any favors then. Protein is pretty much the last nutrient your body needs before exercising, Nyree Dardarian, EdD, RDN, LDN, an assistant clinical professor and director of the Center for Nutrition & Performance at Drexel University, tells SELF.

What you really want pre-workout is carbs, ideally within a few hours of your workout, because they quickly give you the energy you need to power through your routine. Protein, on the other hand, “slows down digestion and interferes with your carbohydrate digestion,” she says. As a result, taking in too much of it pre-workout can make you feel nauseous. Don’t get us wrong—protein shakes are definitely a healthy snack, since they aid with recovery and muscle-building and help keep you satisfied—but they’re best used after your workout, says Dardarian.

Fried foods

Delicious as they may be, doughnuts and fries might not be the best choice right before your hot yoga class. When you work out, you want blood to flow freely throughout your body—to your muscles, your heart, brain and lungs. Blood powers up your muscles so you can reach that PR or hit a tricky pose.

Fried foods are tough to digest, though, so when you munch on chicken fingers, blood rushes to your stomach to aid with digestion. This reduces the amount of blood reaching your arms and legs. “You don’t want your body to be focusing on digestion and taking blood flow away from the rest of your body during your workout,” Long says. The result: You might feel like you’re giving 100%, but you might not be able to do as many reps or run as fast. “It’s like putting crappy gas into your car and expecting it to last forever,” Long says. What’s more, because your body is working hard to digest those kinds of foods, it can make you feel lethargic.

Nuts and avocados

Nuts and avocados are rich in monounsaturated fat, and while that might be good for your heart health, it might not be quite so helpful for your workout if you nibble on them prior to your cardio dance class, Dardarian says.

Fatty snacks take a while to be digested and, similar to fried foods, can mess with blood flow throughout your body. Snacking on a bowl of almonds can reroute blood flow away from your brain, heart, and extremities, says Long. And like we mentioned, if it’s still sitting in your stomach when you’re exercising, it can give you nausea or heartburn, or even make you feel bloated.

Is a handful of walnuts going to absolutely obliterate your workout? No. But “it can leave you feeling heavy and slow,” says Dardarian.

High-fiber bars, granola, or cereals

Eating more fiber in general can do wonders for your gut health, cholesterol, and blood sugar levels. But unless you don’t mind booking it into the nearest porta-potty mid bike ride, hold off the fiber-rich cereals until you’ve logged your miles. The reason: It can make you poop, and “nobody wants that in the middle of a workout,” Dardarian says.

Your body can’t absorb or digest fiber, so it passes right through your gut. Then couple that with the fact that exercise makes your gut muscles contract, and you can see why you might be searching for a toilet, stat.

Best case scenario, having a bowl of fiber-heavy cereal will just give you a normal bowel movement before your workout. But many people who graze on bran flakes ahead of their exercise wind up with the runs or, if they’re not drinking enough fluids, backed up. Because of this, Dardarian says that professional athletes are trained to avoid fiber entirely the day before and morning of a big game or race. “That’s when everyone has white pasta and white bread, as they contain less fiber,” she says.

A glass of milk, a hunk of cheese, or any other dairy-based treat

If Michael downing a pan of fettuccine Alfredo before Dunder Mifflin’s fun run hasn’t forever turned you off to a pre-jog dairy-based snack, then you might be one of the lucky ones who can stomach dairy before bouncing around on a treadmill. But for most folks, it doesn’t go so well.

That’s because dairy, which contains both protein and fat, can agitate your GI system, even if you’re not lactose intolerant and especially if you’re working out in hot weather, says Long. Maybe, like Michael, you’ll feel like you have a ton of bricks sitting in your stomach. Or worse, you puke it all up. Because of this, Long, who previously worked with the Chicago Cubs, advised players to avoid milk, cheese, and yogurt on gameday.

So what should you eat before a workout?

In general, the best thing to eat soon before working out—whether that be taking your dog on an easy walk, doing hot yoga, or running a half marathon—are simple carbs. They’re the easiest thing for your stomach to break down and, unlike protein that takes a while to be converted into energy, give you instant fuel. “Carbs help your body operate more efficiently so you can exert more power with less effort,” says Long. “I call it bang for your buck.” If you need help whipping up a plan, check out SELF’s pre-workout meal and snack guide.

But one thing to keep in mind is that everything here comes with one major caveat: Foods can have vastly different effects on different people. For instance, Dardarian says her daughter isn’t a big fan of breakfast, so she opts for cheese (yep, dairy) and crackers (some fiber in there!) before field hockey practice. It doesn’t make her feel sick and it gives her the carbs she needs to perform. Would Dardarian recommend this combo for everyone? No, of course not, she says.

So yep, consider these recommendations general guidelines, but remember, how you eat before a workout is very individualized. Experiment with different foods—remember, “nothing new on race day” though, so save your tests for a lesser-stakes day—and tune in to how you feel. You just might find the best way to fuel a workout for your body.