Determining Your Calorie Needs
Proper nutrition forms the foundation of a successful marathon training regimen. Insufficient caloric intake can result in fatigue, reduced recovery, and increased injury risk. Conversely, excessive intake can lead to undesired weight gain. Total daily energy expenditure (TDEE) is a combination of the basal metabolic rate (BMR) and the activity level, which increases during marathon training.
Calculating Your Baseline Calories
Before considering mileage, it's vital to determine the baseline metabolic rate. Online calculators, such as those using the Mifflin-St Jeor or Revised Harris-Benedict formulas, can estimate BMR.
- Mifflin-St Jeor Formula:
- Men: $(10 \times \text{weight in kg}) + (6.25 \times \text{height in cm}) - (5 \times \text{age in years}) + 5$
- Women: $(10 \times \text{weight in kg}) + (6.25 \times \text{height in cm}) - (5 \times \text{age in years}) - 161$
Adjusting for Training Intensity
After determining BMR, multiply it by an activity factor corresponding to the marathon training volume. Runners typically burn approximately 100-120 calories per mile, which must be added to baseline requirements. During training, the activity factor will increase from 'moderately active' (1.55x BMR) to 'very active' (1.725x BMR) during peak weeks. For longer runs, it's more accurate to add the estimated calories burned during the run to the daily total.
Macronutrients for Marathon Training
Marathon training requires a specific ratio of macronutrients to meet energy needs, facilitate muscle repair, and support overall health.
Carbohydrates: Fuel for Performance
Carbohydrates are the body's most efficient fuel source during endurance exercise, stored as glycogen in muscles and the liver. Marathoners require significantly higher carbohydrate intake than those with sedentary lifestyles.
- Recommendation: 5-10 grams of carbohydrates per kilogram of body weight each day, adjusted for training intensity.
- Sources: Whole grains (oats, brown rice, quinoa), starchy vegetables (sweet potatoes), fruits, and simple carbs like gels or sports drinks during runs.
Protein: Essential for Recovery
Protein is critical for repairing muscle tissue damaged during intense training and fostering training adaptations.
- Recommendation: 1.4-1.8 grams of protein per kilogram of body weight per day.
- Sources: Lean meats, fish, eggs, dairy, legumes, tofu, and nuts.
Fats: Sustained Energy Source
Healthy fats provide sustained energy, particularly during longer, lower-intensity runs, and support hormone production and vitamin absorption.
- Recommendation: Generally, 20-30% of total daily calories.
- Sources: Avocado, olive oil, nuts, and fatty fish such as salmon.
Hydration and Electrolytes
Staying Hydrated
Adequate fluid intake is crucial for marathoners. Dehydration can hinder performance and increase fatigue. Drink water consistently throughout the day and replenish fluids lost during training. Monitoring urine color, aiming for pale yellow, is a good way to gauge hydration levels.
Electrolyte Replacement
Heavy sweating depletes electrolytes like sodium and potassium. For runs exceeding 60-90 minutes, especially in warm conditions, replenishing these minerals with electrolyte drinks or salt tabs is essential to prevent cramping and maintain fluid balance.
Sample Daily Calorie Adjustments for a 150lb (68kg) Runner
The table below illustrates how a runner's daily caloric needs fluctuate with different training volumes, assuming a baseline BMR of approximately 1,500 kcal.
| Training Volume | Caloric Needs (Approximate) | Primary Purpose | Macronutrient Focus |
|---|---|---|---|
| Easy Day (Rest or <60 min run) | 2,300 - 2,500 kcal | Recovery & Baseline | Balanced Macros |
| Moderate Day (60-90 min run) | 2,700 - 3,000 kcal | Fuel & Replenish | Higher Carbs |
| Hard Day (90-180 min run) | 3,300 - 4,000 kcal | Fuel & Endurance | Highest Carbs |
| Peak Week (High Volume) | 4,000+ kcal | Maximize Glycogen | Carb-dense meals |
Timing Your Nutrition
Carefully timing meals and snacks can substantially affect performance and recovery.
Pre-run Fueling
Focus on easily digestible carbohydrates before a run, particularly for longer ones. Consume a substantial meal 3-4 hours prior to a long run (90+ minutes), followed by a smaller, carbohydrate-rich snack 1-2 hours before starting.
- Examples: Oatmeal with banana and honey, a bagel with peanut butter, or toast with jam.
During-run Nutrition
For runs over 60-90 minutes, start consuming carbohydrates early on. Most runners should aim for 30-60 grams of carbs per hour, increasing to 60-90 grams per hour during longer events.
- Examples: Energy gels, sports chews, sports drinks, or easy-to-carry foods such as bananas.
Post-run Recovery
The body is best at absorbing nutrients within 30-60 minutes post-run. A combination of carbohydrates and protein helps replenish glycogen stores and repair muscle tissue.
- Examples: Chocolate milk, a smoothie with protein powder and fruit, or eggs on toast.
Practice and Consistency
Avoid experimenting with new foods or supplements on race day. The golden rule is to practice the fueling strategy during training runs. This approach conditions the gut to handle fuel while exercising and helps determine what works best. A detailed guide on training nutrition strategies from a reliable source can help refine the plan, such as the information published by the National Institutes of Health.
Conclusion
Determining how many calories a person training for a marathon should eat is not a static calculation, but a dynamic process that evolves with the training regimen. It requires a balanced approach to match baseline caloric needs with the increased energy demands of running, ensuring sufficient intake of carbohydrates, protein, and healthy fats. Careful attention to body signals, consistent practice of the fueling strategy, and adjustments based on run intensity and duration can optimize energy levels, improve recovery, and establish the physical foundation needed to complete a marathon successfully. A personalized strategy, potentially with guidance from a sports dietitian, is the most effective way to align nutrition perfectly with training goals. For additional insights, consider exploring the resources provided by the World Marathon Majors.
