You’re practically in your running shoes, ready to hit the track for your speed session before the alarm goes off. But in your haste to get out the door, do you stop for breakfast? Or do you simply grab a sports gel and get on with it? Some athletes prefer to push through a workout on empty, and focus on post-workout fuel to rebuild and recover muscles. While others need some gas in the tank. What’s best for you might come down to personal preference, but when a PR is on the line, nutrition could give you an edge. Which begs the questions: Should you eat before you work out? And, if so, what?

“It’s hard to give a do-or-don’t, yes-or-no answer,” sighs Lauren Antonucci, RD, specializing in sports nutrition. “What are your goals? And what did you eat for dinner last night?” On the most basic level, what you eat gives you energy. The right foods can boost your workouts, as well as make them a more pleasant experience. And at a competitive level, that pre-workout snack is an important factor to prevent fatigue and fuel performance.

If you’re short on time and just trying to squeeze in a quick sweat session before work, Antonucci says, don’t even worry about food. Just drink some water and get out the door. If you’re stepping it up with your workouts, running farther, hitting a harder spin class, or working out with a trainer, you might want to grab something. That’s especially true if you didn’t have a great dinner last night, and wake up starving. But don’t overthink it—you just need a few bites of carbs.

When you’re working out for more than an hour, doubling up on workouts, or training for a marathon, triathlon, or other competition, you need to put some thought into your pre-workout fuel. The Academy of Nutrition and Dietetics has an official recommendation when it comes to carbo-loading for an event: 1 to 4 g of carbs per kg of body weight, consumed 1 to 4 hours before exercise. For a person of average weight (150 pounds), that means 68 to 272 g of carbs, or 272 to 1,088 calories! And that’s why the pros reach for gels, sports drinks, honey, jam sandwiches, and other sweet tricks—it’s simply hard to take that much in.

For her performance athletes, Antonucci also pushes protein—just a little bit. Protein really comes into play as a workout recovery food, but Antonucci and other experts believe in the benefits of powering up early. Carbs offer energy, but protein is the first step toward muscle recovery, getting amino acids moving in your bloodstream, so they’re immediately available to replenish tired muscles. For endurance and strength-training work, Antonucci recommends taking in 6 to 8 grams of protein, along with your carbs before exercise.

Still, no one is suggesting you eat a cheeseburger right before a long run. (Collective ugh.) “If I have an athlete who’s training for a marathon,” explains Antonucci, “My first question is, ‘What time does the race start?’ The best timing is simply what works best with your schedule—what’s going to be the least disruptive, that leaves you feeling good.” If you’re going to be working out in the next 30 minutes, she recommends a snack-sized 100 to 200 calories of carbs. If you won’t be working out for a few hours, that looks more like a meal, at 500 calories. And of course, you can slide that scale in between.

Gut check: Dairy doesn’t work for everyone. Milk and yogurt offer a balance of carbs and protein, so they’re great foods for athletes. But Antonucci says that many of her athletes report gastrointestinal distress when they eat dairy right before a workout, so she often recommends enjoying it at other times of day. Foods high in fiber and fats (even healthy fats!) may not do you any favors, either. Whole nuts, whole grains, and high-fiber fruits and veggies are slower to digest, which is usually a good thing, giving you energy over time. But right before a workout, that energy won’t be available to you—it’ll be sitting in your stomach. So, skip the full fat Greek yogurt and granola bars. Save those hummus and carrots for later. But you do have permission to raid your toddler’s pantry stash. Antonucci is all about those easy-to-digest carbs, or as she likes to call them, “Kid food! Graham crackers and animal crackers, bunnies and teddy bears, and o-shaped cereal are actually great options.”

It’s the afternoon snack that most people struggle with. If you’re going to work out in half an hour, and you’re sweating for less than 90 minutes, stick with carbs and just grab a banana, piece of toast, or a handful of cereal. But if you’re pushing the length and intensity, you might want to add in a bit of protein and ramp up the carbs.

• Banana with 1½ tablespoons peanut butter | 32 g carbs, 7 g protein, 246 calories

• ½ cup oatmeal with 1 tablespoon peanut butter | 32 g carbs, 9 g protein, 248 calories

• Toaster waffle with 1 tablespoon each nut butter & jam | 31 g carbs, 7 g protein, 242 calories

• 1 slice toast with 2 teaspoons peanut butter, 1 teaspoon honey & ½ banana | 33 g carbs, 7 g protein, 207 calories

• 1 cup o-shaped cereal with ½ cup nonfat milk | 28 g carbs, 8 g protein, 155 calories

• Fruit smoothie with ½ banana, ½ cup mango, ½ cup nonfat yogurt | 35 g carbs, 8 g protein, 171 calories

• 2 slices toast with 1 large egg & 1 tablespoon ketchup | 28 g carbs, 13 g protein, 237 calories

• 14 animal crackers & part-skim string cheese | 27 g carbs, 10 g protein, 241 calories

• ½ protein bar & ½ cup grapes | 31 g carbs, 11 g protein, 198 calories

If either dairy or nut butters don’t agree with you, skip those options. At the end of the day, the perfect pre-workout food is a personal choice. Keep it simple and stick to portions that are going to sit well in your stomach. And of course: Wash it down with water.