TDEE Calculator for Marathon Runners & Endurance Athletes
Marathon and endurance runners have some of the highest calorie requirements of any athlete. A single long run of 20+ miles can burn 2,000–3,000 kcal on top of your base TDEE. Undereating is a leading cause of injury, illness, and poor race performance in distance runners. This calculator helps you establish a solid calorie floor so you can train hard and recover fully.
Marathon runners have some of the highest calorie needs of any athlete. During peak training, weekly mileage of 80 to 120 km can push daily energy expenditure above 3,500 calories, even for smaller runners. The challenge is fuelling these demands without digestive issues during runs. Most of your calories should come from carbohydrates, which are the primary fuel source for aerobic endurance exercise. A typical marathon training diet consists of 55 to 65 percent carbohydrates, 20 to 25 percent fat, and 15 to 20 percent protein. Underfuelling is a common and dangerous mistake among distance runners, leading to a condition known as RED S, or Relative Energy Deficiency in Sport, which causes hormonal disruption, bone stress fractures, and declining performance.
- Choose very active to extremely active for your activity multiplier during peak training blocks with high weekly mileage.
- Eat 6 to 10 grams of carbohydrates per kilogram of body weight during heavy training weeks. Carbs are your primary fuel for endurance.
- Don't neglect protein. Runners need 1.4 to 1.8 grams per kilogram to support muscle repair from the repetitive impact of running.
- If you're losing weight unintentionally during training, you are underfuelling. This increases injury risk and hurts performance. Eat more.
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