Smart fuelling for long runs

It’s that time of the year where many people are increasing their long run and/or making them more strenuous with added target pace sections. I thought it would be useful to give some pointers about how to approach this from a run fuelling perspective, as it’s a vital component which can make or break your session, as well as a training opportunity in itself.

Understanding the two goals

When approaching long run nutrition, we're actually working toward two distinct but complementary goals:

1. Fat adaptation - Training your body to more efficiently use fat as fuel, which is critical for endurance events

2. Practicing race day fuelling - Getting your body accustomed to processing carbohydrates during exercise

These might seem contradictory - and in some ways they are - which is why we need a strategic approach that incorporates both.

Our dual fuel system

Think of your body as having two fuel tanks: glycogen (stored carbohydrates) and fat. Glycogen is stored primarily in your muscles and liver, providing about 1,500-2,000 calories of readily accessible energy. Your fat stores, by contrast, contain upwards of 40,000 calories - even in lean runners.

The catch? Your body naturally prefers glycogen for higher-intensity efforts because it converts to energy more efficiently. Modern diets, with their constant carbohydrate availability, reinforce this preference. But glycogen stores are limited and can become significantly depleted during a marathon, leading to that dreaded "hitting the wall" sensation as your body struggles to maintain energy output.

This is where fat adaptation becomes crucial. By strategically training your body to better utilise its fat stores, you're effectively accessing a second, much larger fuel tank. It's not about eliminating carbohydrate use - it's about developing metabolic flexibility, allowing your body to efficiently draw from both fuel sources. The better you become at utilising fat, the more you can preserve your limited glycogen stores for when you really need them.

Your long run fueling decision tree

Below is how you can approach your upcoming long run that enables you to maximise the session in terms of completing it feeling strong, and training your dual fuel system:

Is this an easy long run or workout-based long run (with MP segments)?
|
├── EASY LONG RUN
|   |
|   └── Did you eat breakfast?
|       |
|       ├── YES
|       |   |
|       |   └── Run duration?
|       |       |
|       |       ├── Under 90 minutes
|       |       |   └── No in-run fueling needed (bring emergency gel just in case)
|       |       |
|       |       └── Over 90 minutes
|       |           └── Take fuel after 90 minutes
|       |
|       └── NO (fasted)
|           |
|           └── Run duration?
|               |
|               ├── Under 60 minutes
|               |   └── No in-run fueling needed
|               |
|               └── Over 60 minutes
|                   └── Take fuel after 60 minutes
|
└── WORKOUT-BASED LONG RUN
    |
    └── Did you eat breakfast?
        |
        ├── YES
        |   └── Take fuel 10-15 minutes before MP segment begins
        |       + Consider additional fuel if multiple MP segments
        |
        └── NO (fasted)
            └── Take fuel 30 minutes into run
                + Additional fuel 45 minutes later and thereafter if multiple MP segments

Making it practical

What exactly do I mean by "fuel"? This can be:

• A gel (easiest option for most)

• Real food (dates, banana, etc. - best reserved for very long, easy runs)

• A carb drink (my preference as it also provides hydration, and is a lot cheaper than gels - I use Tailwind in a soft flask)

Water is non-negotiable for any long run. Hydration supports both performance and recovery, and can make fueling more effective by helping transport nutrients.

Why this matters

When we strategically manage our fueling, we're actually training two systems:

1. By occasionally doing moderately long runs with minimal fueling, we enhance fat metabolism

2. By fueling our harder or longer sessions, we train the gut to process carbohydrates during exercise, as well as ensure that we don’t push our bodies too hard and compromise our recovery

I strongly recommend a mixed approach. The body adapts best when we give it varied stimuli - sometimes asking it to rely more on internal fuel stores, other times practicing the skills of taking on external fuel.

After the session

Whatever approach you take during the run, there's one absolute rule: Refuel properly when you finish. This isn't optional! Eat something substantial within 30 minutes of finishing your long run. This kickstarts recovery, replenishes glycogen, and helps prepare your body for the training days ahead.