Carb loading before a marathon means filling muscle and liver glycogen stores with very high-carb eating. According to Tufts University, runners load for 36–48 hours before the race with tapered training and build meals around white rice, pasta, bagels, and bananas Tufts University carb-loading guide. Glycogen is limited fuel that runs out before fat. A full store delays hitting the wall during efforts over about 90 minutes.
Medical information disclaimer: This article is for general educational purposes only and does not provide medical advice, diagnosis, or treatment. Always consult a physician or other qualified health professional about symptoms, medications, tests, or treatment decisions.
Table of Contents
- When should you start and stop?
- How many carbs do you need?
- What should loading meals look like?
- What should you eat on race morning?
When should you start and stop?
Start loading 36–48 hours before race day and taper training during the same window. This combination maximizes muscle and liver glycogen for endurance fuel.
According to Harvard Health Publishing, finish the heaviest loading about 12 hours before the start. That gap allows digestion and storage, so you line up fueled rather than full.
How many carbs do you need?
According to Tufts University, citing ACSM guidance, the loading target is about 10–12 grams of carbohydrate per kilogram of body weight per day. For a 70-kg runner, that is roughly 700–840 grams of carbs daily.
That amount is far above normal eating, so carbs must dominate every meal and snack. Spread intake across breakfast, lunch, dinner, and snacks to make the total manageable.
What should loading meals look like?
Choose low-fiber, low-fat carbs that digest easily and reduce GI upset. According to Canadian Running Magazine, useful choices include white rice, white pasta, white bread, peeled potatoes, bagels, oatmeal, bananas, jam, juice, and sports drinks carb-loading fuelling basics.
Keep fat, fiber, and large salads low for these two days. Eat familiar foods and avoid trying new products right before the race.
- Breakfast: bagel with jam and banana, or oatmeal with honey and juice
- Lunch and dinner: white rice or pasta with a small portion of lean protein
- Snacks: toast, rice cakes, applesauce, honey or syrup, sports drink
What should you eat on race morning?
Eat a familiar low-fiber carb meal 1–4 hours before the start. According to Sanford Health, aim for 1–4 grams of carbohydrate per kilogram, or about 70–140 grams for a 70-kg runner, plus fluids marathon-week nutrition guide.
Shorter races do not need this process, says Science in Sport. Expect 0.5–1 lb of extra weight and a full feeling from water stored with glycogen; that is normal fuel, not overeating.