The Runner's Complete Guide to Race-Day Fueling: From Training to Finish Line

You've logged the miles, conquered the long runs, and fine-tuned your pacing strategy. But here's the hard truth: all that training means nothing if you bonk at mile 20 because you didn't fuel properly.

Marathon nutrition can feel overwhelming. Walk into any running store and you're confronted with walls of gels, chews, drinks, and bars, each promising to be the key to your best race. Add in conflicting advice about carb loading, hydration protocols, and fueling windows, and it's enough to make you want to just wing it on race day.

Don't. A strategic fueling plan is as essential as your training plan, and getting it right can mean the difference between crossing the finish line strong or crawling through those final miles.

Understanding Your Body's Fuel Tank

Muscle glycogen provides the key fuel for training and racing a marathon, and carbohydrate loading can enhance performance by allowing you to run at optimal pace for a longer period before fatiguing. Think of glycogen as your body's battery. Your body can store approximately 500g of glucose as glycogen in skeletal muscles and about 100g in your liver.

The challenge is this: those stores fuel roughly 90 to 120 minutes of running at marathon pace. Most recreational marathoners are out there for three to five hours. The math doesn't work unless you have a plan to refuel along the way.

Research from a 2025 Sports Medicine-Open study of 160 Seville Marathon runners found that those who met carbohydrate intake recommendations during the race (60 to 90 grams per hour) were more likely to finish in under three hours compared to runners who didn't hit those targets. The science is clear: fueling matters.

Close-up of energy gels, sports drink bottle, and running nutrition products laid out on wooden surface, natural lighting, product packaging visible

The Pre-Race Fueling Window: 2-3 Days Out

Modern research shows there's no need to deplete glycogen stores before loading, and carb loading for just 24 to 36 hours is adequate, especially for trained athletes, with 2 to 3 days pre-race being the sweet spot for most recreational marathoners.

Forget the old-school depletion phase that left runners exhausted and cranky for days. The current approach is simpler and more effective. Research shows adequate carbohydrates to fully load glycogen stores are 10 to 12 grams per kilogram for 2 days or 8 grams per kilogram for 3 days. For a 70kg (154-pound) runner, that's 560 to 840 grams of carbohydrate per day during the loading phase.

What does that actually look like on your plate? More than you think. You'll need to prioritize carbohydrate-rich foods at every meal and snack. Research published in the Journal of Applied Physiology shows you should focus on fast carbohydrates, refined sugars, white rice, and starches that digest easily, with white bread, pasta, potatoes, and rice as go-to foods.

Yes, that means temporarily swapping your usual whole grains for refined carbs. Low fiber and low fat options are ideal for carb loading before a marathon because avoiding high fiber and high fat options aids digestion and means you can eat the large volume required without feeling too full.

Practical Carb Loading Tips:

Spread your intake throughout the day (three meals plus three snacks)
Consider making lunch your largest meal the day before an early morning race
Drink some of your calories (sports drinks, juice, lemonade)
Stay well hydrated (carb loading requires extra fluids)
Accept that you'll gain 1 to 2kg of water weight (this is normal and beneficial)

Race Morning: The Final Top-Up

Aim for at least 100 grams of carbohydrates for breakfast, eaten 3 to 4 hours before the start, though 2 to 3 hours before might work if you don't suffer from gastrointestinal distress. This meal replenishes liver glycogen depleted during your overnight fast.

Your breakfast should be familiar, tested multiple times during training, and easy to digest. Popular choices include bagels with jam, oatmeal with honey, white toast with banana, energy bars, or even rice with a bit of salt.

Bring a water bottle to sip and a gel to take in the 15 minutes before the race starts. That pre-race gel will become available energy about 30 to 45 minutes into your run, right when you need it.

Overhead view of marathon start line with thousands of runners packed together, colorful race bibs, early morning light

During the Race: Fueling for Performance

This is where your strategy becomes critical. The general recommendation is to consume 30 to 60 grams of carbohydrates per hour, which could include two one-ounce bags of sport beans or two energy gels. Your body can comfortably absorb a maximum of 60 to 90 grams of carbohydrates per hour, with elite runners often targeting the higher end.

Timing Your Fuel Intake

For most people, start fueling 30 to 45 minutes into the run to get a head start on your glycogen storage. Don't wait until you feel tired. By then, you're already behind and playing catch-up is nearly impossible.

Studies suggest taking 25 to 30 grams of carbohydrate (the equivalent of one energy gel) every 30 to 45 minutes. Some runners perform better taking smaller amounts more frequently, every 15 to 20 minutes. This is individual and requires practice.

Energy Gel Essentials:

How they work: Energy gels are essentially liquid carbohydrates, most based on maltodextrin made from corn starch combined with fructose, which are simple sugars that bodies can digest quickly.

How many you need: For a half marathon (1.5 to 2.5 hours), plan for 2 to 4 gels spaced 30 to 45 minutes apart, while marathons (3 to 5 hours) require 4 to 8 gels depending on your fueling needs and tolerance.

Practical considerations: Mix your sources. Combining gels with sports drinks can help you absorb more carbohydrates and prevent flavor fatigue. Calculate your total needs based on your projected finish time and bring extras in case the race doesn't go as planned.

Hydration: The Other Half of the Equation

For most runners, aim for 60 to 90 grams of carbohydrates per hour, 200 to 500mg of sodium per hour, and 5 to 10 ounces of fluids every 15 minutes during races over one hour. Hydration and fueling work together. Dehydration can worsen stomach issues and reduce gel effectiveness, so sip water regularly.

Sports drinks serve double duty, providing both hydration and carbohydrates. Factor this into your total carb intake so you don't exceed your body's absorption capacity.

The Golden Rule: Practice During Training

Practicing fueling techniques on long runs prior to your race is critically important because you need to figure out what your stomach can handle and use your long runs as trial workouts, never introducing anything new when you toe the line.

Your gut needs training just like your muscles. You want to train your gut to digest carbohydrates during running, as trying to eat while running for the first time in a race scenario can cause stomach and gut upset.

Start experimenting with nutrition at least 10 weeks before your race. Try different products, test various timing protocols, and simulate race conditions during your long runs. Some runners tolerate gels beautifully. Others do better with chews, waffles, or even real food. There's no single right answer, only what works for your system.

Testing Protocol:

Weeks 10-8: Try different products on easy runs
Weeks 7-5: Practice your planned fueling schedule on long runs
Weeks 4-2: Fine-tune timing and amounts at marathon pace
Race week: Stick with what you know works

Check your race's website or contact organizers to learn what will be available at aid stations. Many races supply water, Gatorade, and gels at different aid stations, so check if there's a course map that tells you what's available and where to figure out what you need to carry versus what you can grab at aid tables.

Runner's hand reaching for water cup at aid station, volunteers in background, motion blur, race atmosphere

Common Fueling Mistakes to Avoid

Overcomplicating it: Your fueling strategy should be simple enough to execute when you're tired and your brain is foggy at mile 18.

Trying something new on race day: This applies to everything from the brand of gel to the flavor to the timing. Race day is for execution, not experimentation.

Forgetting about caffeine: Research shows caffeine can increase alertness and increase time to exhaustion. If you're a regular caffeine user, plan when you'll take caffeinated gels (many runners save these for the second half).

Ignoring your body's signals: Guidelines are starting points. Some runners need more fuel, some need less. Pay attention during training and adjust accordingly.

Underfueling because you're worried about stomach issues: Athletes who met carbohydrate intake recommendations during competition (60 to 90 grams per hour) were more likely to finish the marathon in less than 180 minutes. The risk of bonking is greater than the risk of minor GI discomfort.

Building Your Personal Fueling Plan

Every runner's plan will look slightly different based on body weight, running pace, stomach tolerance, and personal preferences. Here's a framework to build yours:

Calculate your hourly needs: Target 60 to 90 grams of carbohydrate per hour for most recreational marathoners.

Choose your products: Select 2 to 3 options you've tested thoroughly (gels, chews, drinks).

Map it to your race: If you run 10-minute miles, fuel every three miles. Faster runners can use 4 to 5-mile intervals or set your watch to beep every 30 to 45 minutes.

Account for aid station logistics: Know where stations are located and what they offer.

Pack strategically: Carry what you need in a way that's comfortable and accessible.

If you're looking for races to test your fueling strategy, the 42cal Race Directory offers a comprehensive global database of marathons searchable by location, date, and distance, helping you find the perfect training races leading up to your goal event.

Final Thoughts

Marathon fueling isn't rocket science, but it does require planning, practice, and a willingness to learn what works for your unique physiology. The runners who nail their nutrition strategy don't just survive the final miles. They own them.

Start building your fueling plan now, test it relentlessly during training, and trust it on race day. Your legs might get tired, but with proper fueling, you'll never have to experience that empty-tank, can't-take-another-step feeling of bonking.

The marathon is hard enough. Don't make it harder by showing up with an empty fuel tank.

The Runner's Complete Guide to Race-Day Fueling