Carbohydrates are the most talked-about macronutrient in endurance sport — and the most chronically under-consumed by recreational runners. Most athletes know carbs are important for performance. Far fewer know how many they actually need, or how far short of that target they typically fall.
The numbers are clearer than most nutrition debates. The consensus across sports nutrition bodies is robust. Here’s what the research says.
Why carbohydrates matter for running
Glycogen — the stored form of carbohydrate in your muscles and liver — is the primary fuel for running above easy aerobic pace. At easy effort (below around 65% of max HR), fat can supply a significant portion of energy. As pace increases, the proportion of energy from glycogen rises sharply. At tempo effort or above, glycogen is almost the sole fuel source.
Muscle glycogen is also a fuel sensor: its concentration within muscle cells regulates adaptation to training. Repeatedly training with low glycogen can actually impair the signalling pathways that drive fitness improvements — not just making sessions feel harder, but potentially reducing the training benefit itself.
The key number
Endurance athletes need 6–10g of carbohydrate per kg of body weight per day for general training. Half marathon and marathon runners doing high-volume work need 7–10g/kg/day.
A 70kg runner doing marathon training: 490–700g of carbohydrates per day.
Source: Burke et al., Journal of Sports Sciences; ISSN Position Stand; USU Extension Nutrition
Most recreational runners eating “healthily” consume somewhere between 200–300g of carbohydrates per day. For a serious marathon trainer, this represents a daily deficit of 200–400g — which compounds into chronically depleted glycogen stores, harder-feeling easy runs, and slower recovery between sessions.
Daily targets by training load
| Training level | g/kg/day | 70kg runner | 80kg runner |
|---|---|---|---|
| Light (<1hr/day) | 3–5g | 210–350g | 240–400g |
| Moderate (~1hr/day) | 5–7g | 350–490g | 400–560g |
| Hard/marathon training | 7–10g | 490–700g | 560–800g |
| Race week (carb loading) | 10–12g | 700–840g | 800–960g |
Carb periodisation — matching intake to demand
A flat daily carbohydrate target is a starting point, not a prescription. The more sophisticated approach — and the one that the research supports for performance — is matching carbohydrate intake to training load day by day.
- Hard session days: Upper end of your training-load range, prioritise carbs at every meal
- Easy days: Mid-range, no need to hit the top of the range
- Rest days: Lower end, lean proteins and vegetables carry more of the meal
This is how Kovr’s nutrition engine works: your daily carbohydrate target adjusts based on the previous day’s training load and tomorrow’s planned session. On the day after a hard long run, the target goes up. On a rest day following an easy week, it comes down. The hand portion guide (a fist of rice, two fists of pasta) makes it actionable without a food scale.
The post-run window
Glycogen resynthesis — refilling the tank — is fastest in the 30–45 minutes immediately after a hard or long session. Consuming 1.2g of carbohydrate per kg of body weight in this window produces the most rapid rate of glycogen refuelling. For a 70kg runner, that’s around 84g of fast-digesting carbohydrates within half an hour of finishing.
Practical options: a bagel with honey, two fists of white rice, a large banana with peanut butter, or a glass of chocolate milk. You don’t need an expensive recovery product. You need carbohydrates, quickly, before the next meal.
Kovr adjusts your carbohydrate targets daily based on your actual training load.
Log what you ate by voice. Kovr estimates the macros, tells you what’s left in hand portions, and shifts the target up or down based on yesterday’s session and tomorrow’s plan. No food scales. No calorie counting apps. Just actionable numbers from real data.
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Race week carb loading
For events lasting longer than 90 minutes, carbohydrate loading is supported by strong evidence. The current recommendation is 10–12g/kg/day for 36–48 hours before the race, with a focus on simple, easily digestible carbohydrates to maximise glycogen without GI distress.
Research shows carbohydrate loading can improve endurance performance by up to 3% for events over 90 minutes — meaningful at any level of competitive running. The mechanism is straightforward: you start the race with a full glycogen tank rather than a partially depleted one.
Key race week considerations: switch from wholegrain to white rice and white pasta to reduce fibre and the associated GI risk. Reduce fat intake slightly (fat displaces carbohydrate at high intake levels). Drink enough to ensure the glycogen you’re storing is actually hydrated — glycogen binds water, and staying hydrated is part of loading effectively.
Frequently asked questions
How many carbs should a runner eat per day?
General training: 5–7g per kg of body weight. Marathon training: 7–10g/kg/day. A 70kg runner doing marathon training needs 490–700g of carbohydrates per day.
Do runners need to eat carbs every day?
Yes. Amount should match training load: more on hard days, less on easy days. Carbohydrate periodisation matches intake to need rather than applying a flat daily number.
What happens if runners don’t eat enough carbs?
Depleted glycogen causes early fatigue, elevated heart rate at easy paces, poor recovery, and eventually hitting the wall during long runs. Chronic under-fuelling can also impair training adaptation.
How many carbs do you need to carb load for a marathon?
10–12g/kg/day for 36–48 hours before race day. Focus on simple, digestible carbs and reduce fibre to minimise GI issues.
What are the best carbs for runners?
White rice, oats, pasta, potatoes, and bananas. Pre-race, prefer white rice and pasta over wholegrain to reduce fibre. Post-run, fast-digesting carbs like a bagel with honey or banana aid glycogen resynthesis.