Carbohydrates for Runners: How to Fuel Long Runs Properly by Performance Nutritionist John Gaule
By March, marathon training becomes more demanding. Long runs increase, weekly mileage builds, and fatigue can accumulate. Whether you’re preparing for the Waterford Viking Marathon 10K, Half Marathon or Marathon, this is when carbohydrate intake becomes increasingly important.
Carbohydrates are often misunderstood, but for endurance runners they are central to performance. Getting carbohydrate intake right is one of the most important aspects of effective marathon nutrition.
Why Carbohydrates Matter During Marathon Training
Carbohydrates are stored in muscle and liver as glycogen. They are the primary fuel source for running and become increasingly dominant as intensity and duration rise.
As runs extend beyond 60 minutes (common in many 10K training plans), glycogen availability becomes more limiting, particularly if stores are not fully topped up beforehand.
Shorter, easier runs may not require deliberate fueling. However, as weekly mileage increases and sessions become longer or more demanding, overall carbohydrate intake becomes critical for maintaining energy and supporting recovery.
For long runs, carbohydrates are often essential for maintaining training quality and protecting recovery into the following week. Without adequate intake, runners commonly experience heavy legs, higher perceived effort and slower recovery.
March is often where under-fueling becomes noticeable — training progresses, but nutrition does not always increase to match it.
How Much Carbohydrate Do Runners Need?
As mileage rises, carbohydrate intake should rise alongside it. A practical way to guide this is adjusting portion sizes rather than counting grams.
During moderate training weeks, aim for 1–2 cupped handfuls of carbohydrate per meal such as rice, pasta, potatoes, oats or bread.
As training intensifies particularly for half marathon and marathon runners this may increase to 2–3 cupped handfuls per meal, especially around long-run or harder sessions.
For runners who prefer more structured guidance, sports nutrition recommendations typically range from 5–7g of carbohydrate per kilogram of bodyweight per day during moderate training, increasing to 6–10g per kilogram per day during heavier marathon preparation. The key principle is simple: as training demand increases, carbohydrate availability must increase.
Restricting carbohydrates during peak marathon training is a common cause of fatigue and stalled progress.
What to Eat Before and During a Long Run
Long runs are an opportunity to practice race-day fueling.
For sessions lasting longer than 60–75 minutes, aim for:
• A carbohydrate-based meal 2–3 hours before running
• A small top-up snack closer to the session if needed
Options such as porridge with banana, toast with jam and yogurt, or a bagel with honey provide easily digested fuel and help ensure glycogen stores are topped up.
During longer runs, carbohydrate intake helps maintain pace, delay fatigue and train the gut to tolerate fuel.
- 10K runners may not need fuel during shorter sessions but should consider it for longer efforts.
• Half marathon runners should begin trialing carbohydrate intake during long runs.
• Marathon runners should fuel consistently during most long sessions.
Examples of in-run fuel include carbohydrate gels, sports chews, sports drinks, or small portions of easily digested foods such as jelly sweets or banana. Practicing fueling during training reduces the risk of energy dips and stomach issues on race day.
Fuel for Performance, Not Restriction
As race season approaches, some runners consider reducing calories. While body composition may change during marathon training, increasing mileage while maintaining a calorie deficit increases the risk of fatigue and injury. As workload builds, fueling, particularly carbohydrate timing around key sessions — becomes increasingly important. Performance improves when energy intake supports training demand.
If you’re preparing for the Waterford Viking Marathon and unsure whether your marathon nutrition supports your training, personalised marathon nutrition coaching can make a meaningful difference. As a performance nutritionist at John Gaule Nutrition, I help runners fuel with purpose so they arrive at the start line strong and confident.
March is often where consistent fueling separates steady progress from mounting fatigue. Fuel properly now, and the benefits will carry through to race day performance.
