How to Carb-Load Effectively Before a Marathon

With just a few days left until the Portland Marathon, most of the hard work is already behind you. The long runs are done, the taper is nearly complete, and your body is primed for the challenge ahead. Now it’s about making sure you arrive at the start line with the right fuel.

Carb-loading can make a big difference for marathon day. Carb-loading isn’t new. Even for season athletes, it’s worth revisiting how to do it effectively and avoid mistakes that can take away from all the work you’ve already put in.

Your body relies on stored carbohydrates (glycogen) to fuel endurance exercise. During a marathon, glycogen stores are the primary energy source for your muscles. Without enough, fatigue sets in and performance suffers, often what runners call “hitting the wall.”

1. Timing Is Everything
   Carb-loading should happen in the final two days before the marathon, not all week long. Start increasing carbohydrates about 36–48 hours before the race while keeping meals balanced.
2. Focus on Familiar Foods
   Now isn’t the time to try something new. Stick with foods your body tolerates well during training. Rice, oatmeal, pasta, potatoes, bread, and fruit are simple, effective options.
3. Balance with Protein and Vegetables
   Carbs are the star, but don’t ignore lean proteins and vegetables. Protein supports muscle repair, while vegetables provide fiber and nutrients. Just keep portions moderate to avoid stomach upset.
4. Stay Hydrated
   Water helps store glycogen in muscles. Pair carb-rich meals with steady fluid intake throughout the day to maximize energy storage.
5. Portion, Don’t Pile
   Carb-loading doesn’t mean overeating. Think balanced, frequent meals rather than a single oversized pasta dinner the night before.

The last few days before the marathon are about two things: giving your body rest and giving it fuel. Tapering reduces mileage so muscles can be repaired, while carb-loading ensures those muscles have the glycogen stores they need to power 26.2 miles. Together, they help you line up on race day feeling fresh, fueled, and ready.

Carbs may get the spotlight before a race, but a runner’s overall nutrition plays an even bigger role in long-term performance and injury prevention. Balanced meals with lean protein, whole grains, fruits, and vegetables give your body what it needs to recover from training, support joint health, and reduce inflammation. For many athletes, simple routines like eating a protein-rich breakfast after long runs or staying consistent with hydration throughout the week make a measurable difference.

Instead of overhauling your diet, think of carb-loading as a fine-tune. In the 36–48 hours before race day:

• Choose familiar, easy-to-digest carbs like rice, pasta, bread, potatoes, and fruit.
• Keep meals balanced with moderate protein and vegetables.
• Stay hydrated since glycogen stores best when paired with water.
• Spread intake over smaller, steady meals instead of one oversized dinner.

How many carbs should I eat before a marathon?
Sports medicine guidelines recommend 7–12 grams of carbohydrate per kilogram of body weight in the final 24–48 hours. For a 150-pound runner, that’s about 475–800 grams per day.

What are the best foods for carb-loading?
Familiar, easy-to-digest carbs like rice, pasta, oatmeal, bread, and potatoes are ideal. Add fruit for variety and simple sugars. Avoid high-fat, high-fiber foods that may upset digestion.

Can I eat protein and fat while carb-loading?
Yes because carb-loading doesn’t mean cutting everything else. Include lean proteins and small amounts of healthy fats to balance meals but let carbs make up most of the plate.

What if I feel bloated while carb-loading?
Bloating is common if you suddenly increase fiber or try unfamiliar foods. Stick with simple, familiar carbs, and spread intake across smaller meals throughout the day.

Do I need to carb-load for shorter races?
Carb-loading is most effective for endurance events longer than 90 minutes, like a marathon. For 5Ks or 10Ks, a normal balanced diet is usually sufficient.

In the end, you’ve trained for months. You’ve built mileage, managed recovery, and prepared your body for the challenge ahead. Carb-loading is the final piece of the puzzle and a simple, proven way to help you feel strong from the start line to the finish.

At ROC, our sports medicine specialists support runners through every step of marathon training, from long-run strategies to recovery and injury prevention. If pain or fatigue is interfering with your ability to train or fuel properly, our team is here to help you adjust and protect your long-term health so you never miss a mile.

ROC is a proud sponsor of the 2025 Portland Marathon. This post is part of our “Never Miss a Mile” campaign. To see all of our running tips, please visit our Portland Marathon page.