To eat or not to eat before running is a common running conundrum. Newbies, elites, and ultra-endurance runners alike may be challenged by how and what to fuel their bodies with before stepping out the door. Experienced runners may have a list of go-to fueling foods, but even those staples have the potential to ruin a perfectly good run on a bad day.

Why eat before running?

Research has consistently shown a benefit to fueling before exercise—more energy, delayed fatigue, and hitting harder intensities—especially workouts focused on endurance or high-intensity work. A pre-workout snack ideally provides energy the brain and muscles can use quickly and efficiently, before the body taps into its energy stores (e.g. glycogen in the muscles, or body fat). While some runners can and do run in a fasted state, that’s rarely the best approach. If a runner consistently doesn’t eat before running, they may tap out their energy stores, fatigue sooner, and are at risk of chronically underfueling.

Here are a few things to consider as you decide whether or not to eat before running:

  • – Duration
  • – Intensity
  • – Time of day
  • – Weather

“Don’t feel guilty if you run in a fasting state,” says Jonathan Valdez, registered dietitian and runner. For short or easy workouts, this may suit a runner’s preferences. Duration and intensity are relative to a runner’s fitness level and training goals. It’s likely that a fasted state is only experienced in the morning (or after long periods of sleep), which is also when some runners have a low appetite. And some research supports exercising in a fasted state for easy workouts, if it doesn’t interfere with overall health or training goals.

READ MORE: Are You Overtraining or Underfueling?

What should you eat before running?

This question may have a variety of answers, depending on a runner’s experience, goals, nutrition needs, and the workout du jour. Sports nutrition guidelines provide runners with an arsenal of fueling tools to pick from, but even then, the real trick is finding what foods, or combinations, work best for you.

The body prefers to run off of carbohydrates. Both the brain and the muscles burn carbohydrates efficiently, making them the first recommendation for fueling exercise. Cara Harbstreet MS RD, and former collegiate track athlete, advises runners to reduce high-protein and high-fat foods prior to running. “These nutrients, while necessary and beneficial for athletes, are more complex so they take longer to digest,” Harbstreet says. Carbohydrates, on the other hand, can be digested quickly and more easily turned into energy we can use while on the move.

If a runner is interested in nutrition, chances are most of their carbohydrate sources are high in fiber (e.g. whole grains, vegetables, legumes, fruits, and nuts). This is beneficial throughout the day, but may be problematic to eat before running. Fiber is another nutrient that slows digestion time (akin to protein and fat). For a pre-run snack, this is less than ideal. It may cause digestive discomfort, and delay energy availability to our muscles. A tip for beginners: Reserve most high-fiber foods for a post-run recovery meal, or other meals and snacks.

As a new runner experiments with what to eat before running, they may find that some fiber, fat, and protein are tolerable. For example, a banana with peanut or almond butter is what some runners eat before running. This snack contains fiber, protein, and fat, as well as carbohydrates from both the nut butter and banana. After trying this out a few times, runners may find it holds them over and doesn’t cause any issues on the run.

How to experiment with what to eat before running

1) Don’t stick to one meal or snack for too long!
Runners tend to be creatures of habit, taking comfort in routine and ritual. But I strongly recommend experimenting with different pre-workout meals and snacks. Getting too rigid with pre-exercise foods may lead to anxiety while traveling or running with others, and may reduce the variety of nutrients a runner consumes each week. And some days, those go-to meals or snacks may not sit well in the gut, or even sound appetizing, for whatever reason. I prefer to have a variety of viable options.

READ MORE: Ignore These Food Rules and Run Better

2) Take note of what time you eat before running.

If your workout is long or hard, allow at least a one to two hour window for fueling and digesting. “If you’re closer to exercise opt for just fruit or dried fruit so you don’t feel too full,” recommends Kelly Jones, MS RD CSSD. She adds that GI distress can be caused by not only what you eat before running, but also when you eat. In a rush, Valdez opts for just the glass of milk, omitting the fruit. Experimenting with your meal timing, and race-day timing, is equally important to meal composition.

3) Prioritize high-carbohydrate snacks that are low in fiber, protein, and fat.

Jones suggests oatmeal with fruit or a peanut butter and banana sandwich if there’s a two to three hour time window for fueling and digesting before running. Valdez notes his go-to snack to eat before running is half a banana and a cup of fat-free milk. Harbstreet advocates for choosing any snack that satisfies your taste buds, running goals for the day, and gut. I often go with fruit, toast with jam, or half of a snack bar, depending on what’s available.

4) Eat in proportion to the day’s workout, and give it time.

Longer, harder runs will require more energy. Allow more time before fueling (e.g. up to two hours) on those days. For ultra runners, I often recommend a meal up to three hours before, then a carbohydrate-based snack up to 45 minutes prior to running. If you’re heading out for a shorter or easier run, eating within a 30-45 minute window will probably suffice. Depending on your gut sensitivity, fueling before running may be part of your training—teaching your gut to absorb and digest food prior to and during exercising. Be patient with this process.

5. Keep a log of what works and what doesn’t.

If you’re training for a big endurance or speed goal, practice your race-day fueling strategy often, include a variety of foods, and take notes of how you felt both before and during your run. This can help you identify your best options for long training runs and, most important, your big race day.