For endurance runners, fueling isn’t just about what you eat on race day — it’s about preparing your body in the days before. One of the most effective strategies is carbohydrate loading, designed to maximize glycogen stores so you have the energy to sustain long distances without “hitting the wall.”

Why Carbohydrates Matter

Primary Fuel: Carbs are stored as glycogen in muscles and the liver, the main energy source for running at moderate-to-high intensity.

Storage Limits: The body can store enough glycogen for about 90–120 minutes of steady running. After that, fatigue sets in if fuel isn’t replenished.

Carb Loading Goal: Maximize glycogen storage so the body has more “in the tank” before the race begins.

When to Carb Load

Best for races lasting 90 minutes or longer (half marathons, marathons, ultras).

Not necessary for short races (5K, 10K), where glycogen stores are usually sufficient.

How to Carb Load

Step 1 – Taper Training

  • Reduce training volume in the 3–7 days before race day (depending on distance).
  • Less mileage + high carbs = more glycogen storage in muscles.

Step 2 – Increase Carbohydrate Intake

  • Target 7–12 g carbs per kg body weight per day during the final 2–3 days.
  • Example: A 70 kg runner needs 490–840 g of carbs daily.
  • Spread carbs across meals and snacks.

Step 3 – Choose the Right Carbs

  • Best Sources: Pasta, rice, potatoes, oats, bread, fruit, smoothies, low-fiber cereals.
  • Avoid: Excessive fiber or greasy/fatty foods — they can cause stomach discomfort.

Example Carb-Loading Day (70 kg runner, aiming for ~600 g carbs)

Breakfast: Oatmeal with banana + honey (100 g carbs)

Snack: Bagel with jam (60 g carbs)

Lunch: Rice bowl with lean protein + veggies (120 g carbs)

Snack: Fruit smoothie (70 g carbs)

Dinner: Pasta with tomato sauce + bread (180 g carbs)

Snack: Low-fiber cereal with milk (70 g carbs)

Race Morning Fuel

Eat a carb-rich breakfast 2–3 hours before the start.

Aim for 1–4 g carbs per kg body weight depending on what you can tolerate.

Keep it simple and familiar: bagel with peanut butter, rice with honey, or oatmeal with fruit.

Fueling During the Race

Even with carb loading, glycogen isn’t unlimited. Mid-run fueling is essential for races beyond ~90 minutes.

Guideline: 30–60 g carbs per hour (up to 90 g for elites using glucose + fructose blends).

Options: Energy gels, sports drinks, chews, bananas, or a mix of these.

The Takeaway

  • Carb loading is a proven strategy to maximize glycogen and delay fatigue in endurance races.
  • Best for events lasting 90 minutes or more.
  • Requires both tapering and high carb intake in the final 2–3 days.
  • Combine with smart race-day fueling to sustain energy from start to finish.

Think of carbohydrate loading as filling your fuel tank — so you can run stronger, longer, and finish with power.