Carb Loading Calculator — Race Nutrition by Body Weight

What Is Carb Loading?

Carbohydrate loading (glycogen supercompensation) is a nutritional strategy used before endurance events. By systematically increasing carbohydrate intake 2–3 days before a race, athletes can store 20–40% more glycogen than normal, delaying fatigue and improving performance.

When Does It Matter?

Carb loading provides a meaningful performance benefit for events lasting longer than 90 minutes. For 5K and 10K races, a simple carbohydrate top-up the night before is sufficient.

| Race Distance | Est. Duration | Carb Loading Protocol | | :--- | :--- | :--- | | 5K | 20–45 min | Not required. Eat normally. | | 10K | 40–70 min | Light top-up (5g/kg) the day before. | | Half Marathon | 1h 30m–3h | 2-day moderate loading (7–8g/kg/day). | | Marathon | 3h–6h+ | Full 3-day protocol (9–10g/kg/day). |

The Science Behind Glycogen Supercompensation

Your muscles store approximately 400–500g of glycogen in a rested state. This provides around 1,800–2,000 kcal of energy — barely enough for a 3-hour marathon at race pace. By loading carbohydrates beforehand: * Muscle glycogen stores increase by 20–40% * You effectively delay "The Wall" by 20–30 minutes at target pace * Brain glucose availability is improved, reducing perceived effort

Foods to Use During Carb Loading

Focus on low-fibre, low-fat, low-protein carbohydrate sources: * White pasta, white rice, white bread * Potatoes (no skins), bagels, pretzels * Sports drinks, energy gels, bananas * Avoid: High-fibre foods, cruciferous vegetables, large amounts of fat or protein (all slow gastric emptying and risk GI issues on race day)

Q: Will carb loading make me gain weight? A: Yes — temporarily. Each gram of glycogen is stored with ~3g of water. Expect 1–2kg of additional body weight, which disappears over the race as glycogen is burned. This is normal and desirable.

Q: Should I rest completely during carb loading? A: Yes. Combine high carb intake with reduced training volume (a standard taper week). Exercise during carb loading burns the glycogen you're trying to store.