If you’ve ever felt dizzy or lightheaded during a workout, you’re not alone. I can definitely say that I’ve been there a handful of times.
“Remember, food gives you energy,” Albert Matheny, M.S., R.D., C.S.C.S., cofounder of SoHo Strength Lab in New York City and advisor to Promix Nutrition, tells SELF. “Specifically, carbohydrates are what give you the energy you need for moderate- to high-intensity exercise. If you don’t have enough in your system, you won’t be able to output any significant amount of energy.”
If you’re not fueling properly, “Short term, you’ll feel crummy. Long term, you won’t make progress, you’ll get frustrated, and you’ll start to think exercise is full of false promises,” Rob Sulaver, C.S.C.S., C.S.N., founding trainer at Rumble Boxing and founder/CEO of Bandana Training, tells SELF.
Whether your goal is to build strength, increase endurance, or lose weight, you need to make sure you’re giving your body the fuel it needs. Here are the top signs you’re not eating enough before exercising. Plus, when and what you should eat.
1. You’re dizzy, lightheaded, or lethargic.
“If you do a moderate-high intensity workout without properly fueling, your blood sugar can drop very low, making you feel dizzy or faint,” Matheny explains. You’re also likely to feel straight-up tired or lethargic if you’re not giving your body energy, yet are demanding a lot from it during a tough workout. “If you get dizzy and lightheaded, stop exercising immediately,” Alissa Rumsey, M.S., R.D., C.S.C.S., owner of Alissa Rumsey Nutrition and Wellness, tells SELF. If you can, eat some form of a quick carbohydrate or sugar—like a banana or glass of juice—which can help raise your blood sugar and let you get back to working out. Dizziness is also a symptom of dehydration, so drink some water too.
Though not as common, there are some health conditions that can make you lightheaded or dizzy during a workout, like heart problems or even asthma. If you feel this way often, despite properly fueling and hydrating, it’s worth seeing your doctor.
2. You’re nauseous.
This is usually more of a matter of hydration than fuel, Lauren Antonucci, M.S., R.D.N., owner, and director of Nutrition Energy in New York City, tells SELF. If you’re feeling nauseous, think about how much fluid and electrolytes you’ve had so far that day. It could be that you forgot to drink enough water, or maybe you haven’t had enough salt. Being low on electrolytes (like salt) can result in nausea, among other symptoms like muscle cramps and confusion.
“I see a lot of healthy active women following really low-sodium diets and drinking a ton of water, but that doesn’t really work when it’s summer and you’re working out,” Antonucci says. Sodium is an important electrolyte that’s essential for regulating nerve and muscle function in our bodies. When we don’t have enough (usually because we’ve lost it through sweat), our cells can’t send signals properly, and we experience symptoms like cramping, dizziness, headaches, and nausea.
So if you’ve recently cut back on sodium and have been getting nauseous during exercise, try adding some salt back into your diet, suggests Antonucci. Pickles or soup are a healthier route than potato chips since they’re high in sodium but not saturated fat.
3. You’re not performing as well as you know you can.
If you haven’t had enough to eat that day, “you’ll just feel zapped,” Matheny says. “You won’t be able to hold a fast pace on a run and you won’t be able to move through a circuit with as much speed as you normally would.” In general, you’ll probably feel like you can’t work out as hard as you normally do, Rumsey adds. Which can be really frustrating if you put on your spandex and made it to the gym expecting to get a good workout in.
4. You’re injuring yourself, or even passing out.
This is where things can get dangerous. “If you are under-fueling and are not consuming enough calories and/or carbohydrates, you run the risk of low blood sugar and potentially passing out,” Rumsey says. This naturally puts you at higher risk for injury. “You could fall or trip while running, or, say, miss a lifting motion when you have weight overhead,” Matheny says. “Also, you are more apt to injury in general if you are not at your best/most alert/strongest.”
5. You’re not seeing results.
Whether you’re looking to get stronger, increase your endurance, or lose weight, your success will be impacted if you’re not eating enough. There’s a few reasons for this. “If you don’t eat enough, your body may start breaking down muscle to use for fuel,” Rumsey says. Plus, when you’re not properly fueled, you may be too tired to push through as many reps.
Finally, depriving your body of the fuel it needs may actually mess with your metabolism and make it harder to lose weight. “Your body won’t lose weight if you’re not fueling it right. You’re short-changing it, so your metabolism goes down and your body starts conserving [calories],” Antonucci says. She says when someone is having a tough time losing weight, she tests their metabolic rate in her office, and when someone’s rate is lower than it should be, the first thing she looks at is whether they’re eating enough—sometimes, increasing calories is what helps people end up losing weight.
So when and what should you eat before a workout? Here are some basic guidelines:
Figuring out how soon before a workout you need to eat may take some trial and error, since everyone’s bodies and metabolisms are different. “Depending on what time of day your workout is and what your individual needs are, you can either eat a normal-sized meal two to three hours before a workout or a small snack 30 to 60 minutes beforehand,” Rumsey suggests. “The meal and/or snack should include both carbohydrates and protein with some fat and fiber. If you’re eating less than an hour before a workout, limit the amount of fat and fiber you eat, as large amounts can slow down digestion and cause stomach cramps or nausea.”
In terms of a snack, think pretzels and hummus, a banana or slice of toast with some nut butter, or even a hard-boiled egg and a slice of toast, Rumsey suggests. (Here are 11 more R.D-approved pre-workout snack ideas to inspire you.)
Make sure you’re hydrated, too. “If you’re even slightly dehydrated, you might see a difference in both your workout performance and recovery,” Rumsey says.
And last, but certainly not least, it’s important to make sure you’re fueling and hydrating throughout the day so “your body can repair, recover, and get stronger from the workout you did previously,” Matheny says. “Food is necessary for refilling your stores of glycogen—the form of carbohydrate that is stored within your muscles and is quickly accessible for energy during exercise.” Eating haphazardly throughout the day and then scrambling to make up for it right before a workout won’t let you refill those stores properly, Sulavar says, because “our metabolism isn’t shortsighted. You’ll just end up with a full belly with little usable fuel.” That can impact your workout, too—making you feel slow, heavy, tired, and gassy, he says.
A good rule of thumb: If you haven’t eaten in three or more hours, you need a snack. You may find you need a snack closer to your workout than your friends do, but the truth is that “no one is going to feel good going for a workout” if their last meal was four hours ago, Antonucci says. So listen to your body, give it what it needs, and you’ll be one step closer to reaching your goals, whatever they may be.