It’s every runner’s favorite day of the week—long-run day! You’ve got your most cushioned pair of shoes on, your pump-up playlist blasting and your route mapped out. Nothing but you and the open road ahead, right? Not so fast. As it turns out, you need more than just good vibes and an awesome route to crush your long run. According to Roxanne Vogel, Nutrition and Performance Research Manager at GU Energy Labs, your body needs calories for any run longer than an hour.

But figuring out what type of fuel to consume during a long run can be tricky. The distance you’re running, your rate of perceived effort, your body’s ability to digest certain ingredients and even the weather can all play a role in what you should eat during long runs. We spoke with Vogel to answer these questions so you can avoid bonking on your next big adventure.

Before we dive into what you should eat during a long run, it’s important to understand why you need to eat in the first place. If you’ve ever hit the wall during a race, you’re familiar with the feeling that your legs have filled with lead while your pace slows until you're plodding along like a snail that’s lost its shell. This feeling can be attributed to a variety of factors, like starting out too fast, not being acclimated to current weather conditions and not fueling enough during the run. While you can load up on all the carbohydrates imaginable before you run, you need to also consume fuel along the way to carry you through the later stages of a long run or race.

“We recommend consuming calories, usually carbohydrates, for any runs longer than an hour because the carbs you store in your muscles and liver, known as glycogen, are finite,” Vogel says. “The longer you run, the more you burn through those stores and need some external source of carbohydrates. Energy drinks and gels are a really easy and convenient way to get those calories in once you run out of your own source.”

While drink mixes and gels are certainly the most popular choices among runners, there are a variety of other options.

“There have been several research studies that have tried to figure out what the best form for carbs is,” Vogel says. “It turns out that, as long as you're getting the carbs in, it doesn't really matter what form they are in, whether that's a solid, like a chew, or a liquid, like a sports drink or gel. It's all going to be used by the body and turned into a fuel source.”

You’re likely familiar with the old saying “nothing new on race day,” and this holds true for nutrition as well. It will likely take some trial and error to figure out what type of fuel works best for you, from both a digestive and a logistical standpoint. You’ll want to make sure the type of fuel you use is tolerable, meaning it won’t leave you feeling nauseous or running to the bathroom. The best way to do this is by testing the fuel on a shorter, easier run before bringing it along during a longer effort.

It’s also important to think about what types of fuel you’ll use for different types of runs. For example, if you’re heading out for an easy-paced long run, you can find time to open a packet of chews or chow down on a waffle. But if you’re racing a marathon or half-marathon at high intensity, you’ll want something easier to carry, open and consume, like a gel or a pre-mixed drink in a handheld bottle.

“Energy gels are formulated to be the most concentrated source of carbohydrates and energy that can be fit into that little packet,” Vogel says. “That means we take out any water, but water makes it easier for your body to absorb the gel. Think of your small intestine like a drain, and imagine trying to squeeze the gel through the holes of a drain without any water.”

Some runners don’t want to take gels, chews or drink mixes and prefer to consume real foods during their run. Vogel reminds us that the intensity of the run will come into play, as you likely don’t want to chow down on bananas or dates as you’re huffing and puffing at maximum intensity.

“Bananas, potato chips, soda, and dates are all pretty common at trail and ultra races,” Vogel says. “All of those things can work if the intensity is low enough that you're able to digest the food. When you’re running at a higher intensity, blood is flowing to your muscles and not your stomach to help your food digest. That’s when a sports solution, like a gel, is going to be easier to take down.”

Most energy gels, chews and drinks have time-based recommendations on the packaging. For example, GU Energy suggests consuming one gel every 30 to 45 minutes while running.

Some runners find it easier to consume fuel at certain mileage increments, using their beeping watch as a reminder to chow down. For example, if you take a gel every 5 miles and you know you’re going to run at about a 9-minutes-per-mile pace, you’ll be taking in fuel every 45 minutes. The only downside to this approach is that, if you end up running slower than your expected pace, your body will be waiting longer for that much-needed fuel.

“Ultimately, the time-based recommendations are just a suggestion. It’s all about what's comfortable for you,” Vogel says. “The most important thing is to practice your fueling strategy during long runs as you lead up to your race so you know your gut is prepared to take in those calories during the race.”

While we wish all of our runs could be at an ideal temperature, blazing hot summer months and long, bone-chilling winters are a staple of most runner’s calendars. The weather impacts the way we dress, the time of day we choose to run and, believe it or not, our fueling strategy.

During the hotter months, you should pay extra attention to your fluid intake. You’ll need more than just water to stay hydrated during an extra sweaty run.

“You can lose as much as 3 liters per hour of exercise in some cases, and that means you're losing a lot of sodium,” Vogel says. “You need to make sure you're carrying water and adding electrolytes in there, like an electrolyte drink tab.”

Vogel recommends GU’s new Energy Hydration Drink Tabs as a handy (and tasty!) way to stay on top of your hydration needs.

Not only does the weather influence your hydration strategy, but it can impact the type of fuel you find appealing, too.

“In the summer you might crave something more citrusy and light with a thinner texture, like drinks and gels, where in the winter you might crave something more indulgent or something with a little more substance to it, like a Stroopwafel,” says Vogel.

For some runners, that morning cup of joe just isn’t enough. If you need a little boost of caffeine during your run, there are plenty of nutrition products offering just that.

“Caffeine is known to be a strong performance aid for endurance activities,” Vogel says. “Not only does it help you feel less tired, but it decreases your perceived level of pain, making your run feel easier. Runners should start with a moderate amount of caffeine before exercises, one to two cups of coffee, for example, and then add smaller doses throughout the rest of your run.”

Brands like Maurten, GU and Huma all offer caffeinated gels to put a little pep in your step during your next long run or race. Vogel recommends alternating between a caffeinated gel and a non-caffeinated one throughout the duration of your run.

Remember, there’s no one-size-fits-all approach to fueling for long runs. You’ll likely need to try a few different things before you settle on an efficient routine that makes your tummy happy. The good news is that there are plenty of options out there to choose from. A good idea is to keep a training log detailing what you ate, when you ate it, how your run felt, along with the weather conditions and duration of the run. Looking back on this log can help you get an idea of what’s worked and what hasn’t, so you can dial in your fueling strategy for future runs.