One of the most common race-week mistakes runners make is gorging on a massive, heavy Italian dinner the night before a marathon. By then, it is too late. Your digestive system becomes overloaded, leading to restless sleep and sluggishness on race morning.
Proper carbohydrate loading is a calculated metabolic strategy designed to super-compensate your muscle and liver glycogen stores. When executed correctly, it delays the onset of fatigue and protects your pace when you hit the wall.
The Math: What is a True Carb Load?
Carb loading is not just eating "more" food; it is shifting your macronutrient ratios while tapering your training volume.
- Carbohydrate Target: Aim for 8 to 10 grams of carbohydrates per kilogram of body weight per day during the final 48 to 72 hours. For a 70kg runner, this translates to roughly 560g to 700g of carbs daily.
- Taper Synergy: Because you are dramatically reducing your running mileage during race week, your energy expenditure drops, allowing incoming carbohydrates to be stored directly as glycogen rather than burned immediately.
The 72-Hour Execution Timeline
Step-by-Step Race Week Schedule
- • 3 Days Out (Thursday for a Sunday Race): Begin tapering fiber intake. Shift to low-residue carbs (white rice, white pasta, white bread, sourdough, potatoes without skin) to keep digestion light.
- • 2 Days Out (Friday): The heavy loading window begins. Hit your 8–10g/kg target by spacing carbs across 5 to 6 smaller meals/snacks (e.g., bagels, honey, pretzels, fruit juice, white rice with chicken).
- • 1 Day Out (Saturday): Continue clean, easily digestible carbs. Eat your largest meals earlier in the day rather than right before bed. Drink plenty of water with electrolytes.
Managing the Water Weight Reality
As your body stores glycogen, it also stores water—roughly 3 grams of water for every 1 gram of carbohydrate.
If you step on the scale two days before your marathon and notice you’ve gained 1 to 2 kilograms, do not panic. This is not fat gain; it is proof that your muscles are fully saturated, primed, and holding an optimal internal water reservoir for race day.
Ready to map out your race day execution? Use our General Calculator or explore course guides like the London Marathon Hub to tie your nutrition strategy together.