This article is written by Emily from @twicethehealth. Whether you’re training for your first 10K or aiming to smash your marathon PB, this guide will deepen your understanding of carbohydrate availability and how it affects your running performance.
What is Carbohydrate Availability?
When runners hear “carbohydrates,” their minds often jump straight to carb-loading—that classic pre-race pasta party. But carbohydrate availability is a more dynamic, ongoing concept. It refers to how much usable carbohydrate your body has available at any given moment to fuel performance and recovery.
Carbohydrate availability plays a critical role in:
Sustaining high-intensity exercise
Accelerating post-run recovery
Regulating appetite and energy intake
Supporting immune and hormonal health
Why Carbohydrate Availability Matters for Runners
Your body uses a sliding scale of fuel sources (primarily carbohydrates and fats) based on exercise intensity:
High-intensity running (e.g., intervals or tempo runs) requires carbohydrates.
Very low-intensity jogging (e.g., recovery runs) draws more on fat for fuel.
Moderate-intensity sessions (e.g., steady runs) relies on a mix of carbs and fat.
Even if your overall calorie intake is sufficient, low carbohydrate intake and timing can still impair your performance and health. If you’re underfueled, especially on longer/high-intensity runs, you risk:
Lack of enjoyment and motivation
Reduced ability to hit and maintain your pace targets
Greater fatigue and slower recovery
Weakened immune system
Long-term risk of RED-S (Relative Energy Deficiency in Sport)
Common Causes of Low Carbohydrate Availability
While some endurance athletes experiment with highly-controlled periodised approaches ('train low' and 'race high'), most studies focus on elite male athletes who are well adapted to fat oxidation. Therefore, they are better able to rely on fats for energy provision during low-intensity running.
However, this approach isn’t necessary - or advisable - for the majority of recreational and competitive runners. Simply put, most of us cannot break down fats at a fast enough rate to support low-intensity running. If you're experiencing low carbohydrate availability, this may be due to:
Following a low-carb diet
Consuming most of your carbs in a single daily meal
Not eating before or after key training sessions
Leaving long gaps (3+ hours) between meals
How to Improve Carbohydrate Availability
It's not only important to think about short-term carbohydrate availability to support performance e.g. around a big training session or close to an event/race, but also the long-term balance for everyday training and recovery.
Top tips to improve your carbohydrate availability:
Include complex carbohydrates with every meal (wholegrains, legumes, starchy veg)
Consume a simple, carb-based snack 30-60 minutes before training
Consume 30-60 g/h of carbohydrates (gels, drinks, sweets) during runs lasting 60+ minutes
Within 30-minutes post-run, refuel with a mix of carbs and protein in a 3:1 ratio (i.e chocolate milk, eggs on toast, couscous salad, tofu wrap)
Avoid going < 3 hours without eating
What Counts as a Complex vs. Simple Carbohydrate?
Type | Examples | Benefits |
Complex | Whole grains, pulses, potatoes, beans, brown rice, pasta | Slow release of energy, high in fiber |
Simple | Fruit, dried fruit, sweets, jam, milk, honey, energy gels | Quick energy for before/during runs |
Meal ideas:
Porridge with berries
Bagel(s) with banana and peanut butter
Jacket potato with beans
Couscous and bean chicken salad
Tofu thai green curry with sticky rice
Fajitas with corn tortilla wraps
Snack ideas:
Banana
Fruit yoghurt
Chocolate milk
Crumpet with jam
Soreen/fruit loaf
We hope that can take something from this article. Check out our other nutrition resources.
Emily (one half of @twicethehealth)
ANutr, MSc, BSc