The biggest mistake I’ve made before a half marathon is loading up on too much coffee. I wasn’t much of a coffee drinker at the time, but I was a young and very novice distance runner. I read that coffee could improve both endurance and speed, so I wanted to try it out.

Yet, I neglected to consider my low tolerance for caffeine, or the effects it has on overall hydration. Instead of being smart about my race-day fueling, I filled a 20-ounce to-go cup with a hot brew, and sipped on it all the way to the starting line. Then I drank some water.

This ended up being one of my worst 13.1-mile runs, due to a variety of factors but in no small part thanks to my caffeinated experiment. My lips were dry at the start, and my mouth tasted of coffee for miles on end. I couldn’t figure out how to fight the high, then subsequent low, of the energy buzz. I just hadn’t trained for it!

My experience isn’t the norm, but it’s not far off from what many runners have dealt with on a big race day. Why not try something new? Or have a little more of something that seems to work? It’s really a fantasy search for the magic PR formula, in which the risk is rarely worth the possible (but unlikely) reward.

After polling a group of registered dietitians (RDN) and certified specialists in sports dietetics (CSSD), it’s clear that “experiment” is the one thing we definitely should NOT do on race day. Alternatively, it’s clear the one thing we should definitely do is fuel up. A pre-race meal or snack is a necessity. Practicing this race-day fueling strategy, and knowing what to eat before a run, are both key to a successful training cycle.

Here are additional tips for fueling any race day, from the 5K to the 50K, from sports nutrition experts:

Keep it to your norm for up to 48 hours before race day!

Race day isn’t the only time to focus on keeping things simple. Philadelphia-based dietitian Kelly Jones, CSSD and co-author of Fit Fueling: Mindful Eating for Active Women, cautions runners to stick to their “normal” foods and drinks for up to two days before the race. Make sure you know what’s going through your system, and how you’ll tolerate it as it digests over the course of time.

READ MORE: How to Replace Electrolytes With Real Foods

Plan ahead: Practice your fueling!

Personally, I always have clients take notes during their training, so they can review some of their best runs and how they fueled both before and during those efforts. Practicing race day fueling during long runs, and speed workouts, is key to developing this plan. Running coach and sports dietitian, Lauren Thomas CSSD, stresses this with her clients as well.

“Make a plan and STICK TO IT!” Thomas advises. This can be especially hard during the late miles of a race, when fatigue sets in…or doesn’t. “While it may be tempting to skip aid stations if you are feeling great,” she says, “trust that attention to your nutrition early and often will make for a strong finish.”

Hone in on hydration and sodium.

When hydration is mentioned, it implies a balance of electrolytes and fluids, not just chugging water! Washington DC-based dietitian Lauren Trocchio, CSSD notes, “Many athletes I have worked with are shocked to learn how much [fluid and electrolytes] they’re losing!” And she adds, “few make the connection between dehydration and digestive issues,” both of which could derail race-day efforts quickly. Trocchio recommends staying on top of sodium and hydration, especially during the race.

Caffeinate … if you’re used to it!

My story above is one potential caffeine scenario, but as I mention, I hadn’t practiced this strategy. I’m not shocked it backfired. In the races since, I’ve had a small cup of coffee (8 ounces or less) before a race, if any at all.

Jonathan Valdez, dietitian and certified personal trainer, notes that “research shows that caffeine may assist with your performance during short runs.” However, he emphasizes including caffeine in your training regimen, to be aware of your personal tolerances.

Knowing what kind of drinks and energy gels are on the course in advance will help you refine your fueling strategy. Photo:

Be patient and consistent with your fueling (and hydrating).

For each of my clients, I give them time or mileage markers for fuel—every 35-40 minutes, or every 2 to 4 miles, depending on their pace and personal needs. Consistency can be key, and can help a runner get ahead of their fuel and hydration needs, avoiding the “wall.”

Another tip from Anne Mauney, sports dietitian and co-author of “Nutrition for Runners” suggests eating gels, chews or other energy snacks slowly over the course of a few miles. “This can help to provide more stable energy—and to avoid any gastrointestinal issues during the race!”

READ MORE: How to Develop a Race-Day Fueling Strategy

Know what will be available on the course.

While it’s preferable to have your own tried-and-true fuel and hydration sources, there are plenty of distances during which that may pose a challenge. It’s not easy to carry everything you need for a marathon, or ultramarathon. If it will ease your mental and actual weight load, know what will be available on the course and whether it works for you.

For example: Marine Corps Marathon lists food items by specific aid stations (e.g. gels in a variety of flavors at Mile 12, animal crackers at Mile 24). Almost all races will list the hydration provided (e.g. Gatorade Sport, Nuun, etc.), in addition to having plain water.

If you’re at a local race, or traveling with family or friends, you can also plant them at strategic places on the course to hand you a snack, or filled water bottle.

At the end of your training, NC-based Ritter Sports dietitian Steph Saullo, urges all runners to remember this: “Nutrition is just like another piece of equipment. Don’t forget about it!” Train for your nutrition plan and goals, and execute your fueling strategy with the same energy you put into every goal race pace mile.

READ MORE: Ignore These Food Rules and Run Better