The Science-Backed Carb Loading Strategy Every Marathon Runner Needs
What Is Glycogen and Why Does It Matter for Marathon Runners?
Glycogen is your body's stored form of carbohydrates, kept primarily in your muscles and liver. Glycogen breaks down into glucose as you run, and serves as your main fuel during long-distance efforts—especially in a marathon where sustained energy is key.
When glycogen runs out, your body shifts to burning fat, which is slower and less efficient. This is what causes the dreaded “hitting the wall.”
Carb loading aims to maximize these glycogen stores so you start your marathon with a full fuel tank.
The Optimal Carb Loading Protocol: 36–48 Hours Before Your Race
Instead of a last-minute pasta dinner, research shows it’s better to gradually increase carbohydrate intake 36–48 hours before your marathon.
✅ Recommended intake:
10–12 grams of carbohydrate per kilogram of body weight per day
This slow uptake reduces the chance of excess glucose sitting in the gut (which draws water into the intestines and causes bloating).
Example:
60 kg runner: 600–720g carbs/day
This strategic increase gives your body time to synthesize and store glycogen efficiently.
What Does That Actually Look Like in Food?
You don’t need to overeat—just shift your calorie intake toward carbs.
Note: This is not a “race morning breakfast” - your breakfast on the morning of the marathon should be the exact same thing you have ben eating prior to all of your long runs in training (i.e. high in carbohydrates, low in fibre).
Day 1 Carb Loading Meal Plan
Goal: 10g/kg carbs (~600g) and 1.8g/kg protein (~108g) for a 60kg runner
This plan is based on whole foods, includes vegetables at lunch and dinner, and avoids protein shakes or processed options. All meals are designed for sustained energy and optimized glycogen storage heading into marathon race day.
🥚 Breakfast: Veggie Scramble + Potatoes
- 2 whole eggs
- 3 egg whites
- ½ turkey-feta sausage (~50g)
- Veggies: peppers, mushrooms, onions, spinach
- 1.5 cups baby potatoes or 1.25 cups hashbrowns
Protein: ~30g
Carbs: ~45g
🍌 Morning Snack: Toast + Peanut Butter + Banana
- 2 slices whole grain toast
- 1 tbsp peanut butter
- 1 medium banana
Protein: ~9g
Carbs: ~60g
🥗 Lunch: Quinoa Chickpea Salad Bowl
- ¾ cup cooked quinoa
- ½ cup chickpeas
- 100g grilled chicken
- Chopped cucumber, red onion, mixed greens
- Lemon vinaigrette
Protein: ~40g
Carbs: ~65g
🍓 Afternoon Snack: Oatmeal + Berries + Yogurt
- ¾ cup rolled oats (cooked)
- ½ cup mixed berries
- ¾ cup Greek yogurt (or DF alternative)
Protein: ~20g
Carbs: ~55g
🍣 Dinner: Salmon + Rice Bowl
- 100g air-fried salmon
- 1.25–1.5 cups cooked white rice
- ½ cup edamame beans
- Cucumber + mixed greens
Protein: ~38g
Carbs: ~60g
🧀 Evening Snack: Turkey Pepperoni + Crackers + Grapes
- 2 turkey pepperoni sticks
- 12 whole grain crackers
- 1 cup grapes
Protein: ~12g
Carbs: ~55g
📊 Total Daily Macros
- Total Carbohydrates: ~600g
- Total Protein: ~114g
✅ This whole-food based day hits your marathon carb-loading targets without sacrificing digestion or quality nutrition. Day 2 will follow a similar structure with different food choices to avoid monotony and keep digestion on track.
Why You Shouldn’t Rely on a Massive Carb-Heavy Dinner the Night Before
Big mistake: Waiting until the night before to “load up.”
Why it backfires:
Bloating from water retention
Excess glucose from your meal sits in the GI tract → pulls water into the intestines via osmosis → bloatingDisrupted sleep
Late-night digestion and sugar spikes interfere with recovery.Ineffective storage
Glycogen synthesis takes time; one big meal isn't enough.
However, when you spread your carb intake over 2 days:
Glycogen synthesis occurs gradually, giving muscles time to store both glycogen and water efficiently
Meals are smaller and spaced out, avoiding sharp glucose and insulin spikes
Your gut has time to digest, absorb, and clear food properly between meals
Water associated with glycogen is pulled into muscle tissue, not left floating in your stomach or intestines
Summary: Smart Carb Loading = Marathon Fueling Success
Carb loading is about more than carbs—it's a science-backed strategy to maximize glycogen and give you a performance edge.
Skip the panic pasta dinner. Instead, follow a structured plan:
📆 Start 36–48 hours out
🍚 Aim for 10–12g carbs/kg/day
🚫 Avoid last-minute bloat
✅ Arrive at the start line fueled and ready to go
References
Burke LM, Hawley JA, Wong SHS, Jeukendrup AE. (2011). Carbohydrates for training and competition. Journal of Sports Sciences, 29(S1), S17–S27.
Thomas DT, Erdman KA, Burke LM. (2016). Nutrition and Athletic Performance. Journal of the Academy of Nutrition and Dietetics, 116(3), 501–528.