The final week before a marathon shifts nutritional strategy from training support to performance optimization. This period is designed to maximize the stored fuel your muscles and liver rely on to sustain you through 26.2 miles. Correct fueling involves strategically manipulating your macronutrient intake to super-saturate your body’s energy reserves. This precise diet ensures that the physical work of training is fully supported by the necessary biochemical resources for your best possible race.
Implementing the Carb Loading Strategy
The modern approach to carbohydrate loading focuses on the final two to three days leading up to the race, coinciding with the taper. This strategy aims to elevate muscle glycogen stores beyond their normal capacity, maximizing the body’s most accessible fuel source for endurance exercise. This condensed method is less disruptive to digestion than older protocols and is effective at maximizing energy reserves.
To achieve maximum storage, significantly increase your carbohydrate intake to 8 to 12 grams per kilogram of body weight daily in the 48 to 72 hours before the marathon. This requires shifting your total calorie composition to about 70 to 80% carbohydrate, while reducing the proportion of fats and proteins. The goal is to consume a high volume of carbohydrates without increasing the overall bulk of food, which prevents stomach discomfort.
Prioritize easily digestible, low-fiber carbohydrate sources during this phase to minimize the risk of gastrointestinal issues. Spreading this carbohydrate load across smaller, frequent meals and snacks helps the body absorb the glucose more efficiently for conversion into muscle glycogen. Liquid carbohydrate sources, such as fruit juices or sports drinks, can also help meet the high gram targets without feeling overly full from solid food.
Low-Fiber Carbohydrate Sources
- White rice
- White pasta
- Bagels
- Refined breakfast cereals
- Potatoes without the skins
Hydration and Electrolyte Management
Proper hydration in the week before the race requires balancing fluid intake and maintaining adequate electrolyte levels, especially sodium. Simply increasing water consumption alone can be detrimental, as excessive plain water dilutes the body’s sodium concentration, potentially leading to exercise-associated hyponatremia. Focus on steady, consistent fluid intake throughout the day, rather than consuming large volumes all at once.
Electrolytes, particularly sodium and potassium, are important for nerve and muscle function and for retaining necessary fluids. Runners who are heavy sweaters should consider increasing their sodium intake slightly in the two days before the race. This can be achieved by adding table salt to meals, consuming salty broths, or utilizing electrolyte tablets or sports drinks.
A common strategy is to “preload” with a higher-sodium sports drink the night before and again on race morning, about 90 minutes before the start. This boosts blood plasma volume, providing a larger fluid reservoir once sweating begins on the course. Aim to maintain a pale yellow urine color throughout the week as a simple visual cue of proper hydration.
Foods to Strictly Avoid
The primary objective of pre-marathon nutrition is to maximize fuel stores while minimizing the risk of gastrointestinal distress during the race. Therefore, certain food categories should be strictly eliminated from your diet, especially in the final 48 hours. High-fiber foods are the top priority for avoidance because the undigested bulk can cause bloating, gas, and an urgent need for a bathroom break.
High-fat foods, such as fried items, heavy sauces, and fatty cuts of meat, should also be avoided as they significantly slow the rate of gastric emptying. Delayed digestion means food remains in the stomach longer, increasing the likelihood of nausea or sluggishness during the run.
High-Fiber Foods to Avoid
- Raw vegetables
- Whole grains
- Legumes
- Nuts
- Seeds
Avoid any unfamiliar foods or supplements that have not been thoroughly tested during training runs, as introducing new ingredients risks unexpected intolerance. Runners should also limit spicy foods, excessive caffeine, and sugar alcohols found in “sugar-free” products, as these are known gut irritants that can provoke diarrhea or heartburn.
The Critical Race Day Morning Meal
The final meal before the marathon is the last opportunity to top off liver glycogen stores, which are depleted overnight, and provide readily available energy. This meal must be consumed between one and three hours before the official start time to allow for adequate digestion. The closer the meal is to the start, the smaller and simpler it should be to prevent stomach upset.
The ideal composition is a small, high-carbohydrate, low-fiber, and very low-fat meal. Fat and protein should be kept to a minimum because they slow digestion and divert blood flow away from the muscles. A good target for carbohydrate intake is one to four grams per kilogram of body weight, depending on the time available for digestion.
Concrete, proven examples include a plain bagel with jam, white toast with honey, or a small bowl of low-fiber oatmeal with a banana. Crucially, this meal should be a familiar one, practiced exactly as it will be consumed on race day, including the brand of food and the timing. Utilizing foods successfully processed during long training runs provides assurance that your fuel strategy will not cause a race-day problem.