How to Fuel for a Marathon: A Complete Guide

Training for a marathon takes months of dedication, but how you fuel for a marathon can make or break your performance on race day. Even the most well-trained runner will struggle if their nutrition plan isn’t aligned with the demands of 42.2 km.

Marathon fueling isn’t about eating “perfectly” or following extreme strategies. It’s about providing your body with the right energy, at the right time, in the right amounts to support training, recovery, and race-day performance. In this guide, we’ll break down exactly how to fuel for a marathon in a clear, practical, and evidence-based way.

Why Marathon Fueling Matters

Running a marathon places enormous stress on the body. Glycogen (stored carbohydrate) is the primary fuel for endurance running, yet your glycogen stores are typically limited to around 90–120 minutes of running at marathon intensity.

Without a solid fueling strategy:

• Energy levels drop

• Pace becomes difficult to maintain

• Risk of “hitting the wall” increases

• Recovery is delayed

Good marathon nutrition supports:

• Sustained energy output

• Better pacing and mental focus

• Reduced gastrointestinal distress

• Faster post-race recovery

Understanding Your Energy Needs as a Marathon Runner

Carbohydrates: Your Primary Fuel

Carbohydrates are the cornerstone of marathon fueling. They are stored in the muscles and liver as glycogen and are the most efficient fuel for endurance performance.

General daily carbohydrate targets during marathon training:

• Moderate training days: 5–7 g/kg body weight

• Heavy training or peak weeks: 7–10 g/kg body weight

Examples of carbohydrate-rich foods:

• Rice, pasta, potatoes

• Oats and breakfast cereals

• Bread, bagels, wraps

• Fruit, yoghurt, smoothies

Restricting carbohydrates during marathon training is one of the most common mistakes runners make.

Protein: Supporting Recovery and Adaptation

Protein doesn’t directly fuel running, but it’s essential for muscle repair, immune function, and adaptation to training.

Aim for:

• 1.4–1.8 g/kg body weight per day

• Spread intake evenly across meals and snacks

Good protein sources include:

• Eggs, dairy, yoghurt

• Fish, chicken, lean meat

• Tofu, beans, lentils

Fats: Supporting Overall Energy and Health

Dietary fat supports hormone production and provides a concentrated energy source at lower intensities.

Focus on:

• Olive oil, nuts, seeds

• Avocado

• Oily fish

Avoid very high-fat meals close to training or race day, as they slow digestion.

Carb Loading for a Marathon: What Actually Works

Carb loading is one of the most misunderstood aspects of how to fuel for a marathon.

How to Carb Load Properly

Carb loading should occur in the 36–48 hours before race day, alongside a reduction in training volume.

Recommended intake:

• 8–10 g/kg body weight per day

Key tips:

• Choose low-fibre, familiar carbohydrates

• Reduce very high-fat and very high-protein foods

• Spread carbs evenly across meals and snacks

Examples:

• White rice, pasta, potatoes

• Bagels, white bread, pancakes

• Fruit juice, smoothies

This strategy maximises glycogen stores while minimising gut discomfort.

Marathon Race Day Nutrition: Before the Start

Pre-Race Breakfast (3–4 Hours Before)

Your pre-race meal should top up liver glycogen and provide easily digestible energy.

Aim for:

• 1–4 g carbohydrate per kg body weight

• Low fibre, low fat, moderate protein

Examples:

• Porridge with honey or banana

• Toast or a bagel with jam

• Rice pudding or cereal with milk

Stick to foods you’ve tested during training.

Final Top-Up (30–60 Minutes Before)

A small carbohydrate boost can help maintain blood glucose.

Options include:

• Banana

• Sports drink

• Energy gel

Avoid trying anything new on race day.

Fueling During a Marathon

Fueling during a marathon is essential to delay fatigue and maintain pace.

How Much Carbohydrate Do You Need?

General guidelines:

• 30–60 g carbohydrate per hour

• Up to 90 g per hour for experienced runners who have trained their gut

Sources include:

• Energy gels

• Sports drinks

• Chews or blocks

Practical Fueling Strategy

• Start fueling early (within the first 30 minutes)

• Take small, regular doses rather than large amounts at once

• Combine gels with water to aid absorption

Practising your fueling strategy during long runs is non-negotiable.

Marathon Hydration Strategy

Hydration is a critical part of marathon nutrition, but overhydration can be just as problematic as dehydration.

Key Hydration Principles

• Drink to thirst, not to excess

• Use aid stations strategically

• Include electrolytes for runs over 90 minutes

Sodium helps:

• Maintain fluid balance

• Reduce the risk of hyponatraemia

• Support nerve and muscle function

Avoid trying to “force” fluids; consistency matters more than volume.

Common Marathon Fueling Mistakes

• Under-fueling during training

• Avoiding carbohydrates

• Trying new foods or supplements on race day

• Over-consuming fibre before the race

• Ignoring hydration and electrolytes

A personalised marathon fueling plan can help avoid these pitfalls.

Recovery Nutrition After the Marathon

Post-race nutrition supports muscle repair and glycogen replenishment.

Aim to consume within 60 minutes:

• Carbohydrates: 1–1.2 g/kg

• Protein: 20–30 g

Examples:

• Chocolate milk

• Smoothie with fruit and yoghurt

• Rice or pasta with lean protein

Continue prioritising fluids and electrolytes for the next 24–48 hours.

FAQ: How to Fuel for a Marathon

1. How many carbs should I eat during a marathon?

Most runners should aim for 30–60 g of carbohydrate per hour. Highly trained runners may tolerate up to 90 g per hour if they’ve practised this in training.

2. Should I avoid fibre before a marathon?

Yes. Reducing fibre intake 24–48 hours before race day can lower the risk of gastrointestinal issues. Focus on low-fibre carbohydrate sources instead.

3. Can I run a marathon fasted?

Running a marathon fasted is not recommended. Fasted running increases the risk of early fatigue, reduced performance, and poor recovery. Adequate carbohydrate availability is essential for marathon success.

Are you training for a marathon? Book an initial appointment on WhatsApp via +447888465215 for personalised advice with our sports experts team.