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) relies mostly on carbohydrates.
Low-intensity jogging (e.g., recovery runs) draws more on fat as fuel.
Moderate-intensity sessions (e.g., steady runs) require a mix of carbs and fat.
Even if your overall calorie intake is sufficient, poor carb timing or low carbohydrate proportion can still impair your performance and health. If you’re underfueled, especially on carbs, you risk:
Reduced ability to run at higher intensities
Increased fatigue and slower recovery
Weakened immune function
Long-term risk of REDS (Relative Energy Deficiency in Sport)
Common Causes of Low Carbohydrate Availability
While some endurance athletes experiment with “train low, race high” protocols (training with low carbs to boost adaptation), most studies focus on male elite athletes, often with controlled supplementation like caffeine and carb rinses.
This approach isn’t necessary—or advisable—for the majority of recreational and competitive runners. If you're experiencing low carbohydrate availability, this may be down to:
Following a low-carb diet
Consuming most 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, e.g. around a big training session or close to an event/race, but also long term carbohydrate availability, or everyday training and recovery. It's all about balance.
Top tips to improve your carbohydrate availability:
Include complex carbs with every meal
Eat carb-based snacks 1–2 hours before training
Prioritize simple carbs 30–60 minutes before workouts
Take on carbs during runs lasting 60+ minutes
Refuel within 20 minutes post-run with a mix of carbs and protein
Avoid going more than 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