Carbohydrates for endurance training: how much to eat

Carb ranges for endurance athletes seem to contradict each other: 5 to 12 g/kg, 5 to 10, 7 to 10. In fact, they don't describe the same thing. Some describe a normal training day, others the day before a race, and others what you take in during one hour of effort.

The solid guidelines come from reference documents: the 2016 North American joint position statement, the 2023 IOC consensus, and studies on high doses. Here is how to read them for your own week.

Per day: your need follows the length of your workout

The joint position statement of the Academy of Nutrition and Dietetics, Dietitians of Canada and the ACSM (Thomas, Erdman, Burke, 2016) links carb intake to the load of the day. The figures are in grams per kilo of body weight per day:

To convert g/kg into grams, multiply your weight in kilos by the number you choose. You don't need to aim for the same number every day. The logic, called "fuel for the work required," matches carb availability to the workout ahead. On easy-run or rest days, stay near the low end; on long-run days, go higher.

This guideline dates from 2016. It remains the common base, but the studies on high doses during effort are more recent (see below). The official documents cited here are North American and international. The recent work on high doses comes mostly from European and British teams, with no different official recommendation.

During exercise: a dose per hour, not per kilo

During exercise, you think in grams per hour. Burke and colleagues (2011) showed that the amount of carbs your body can use is not tied to body size, so guidelines can be given as absolute amounts, not g/kg.

Why a mix? Jeukendrup (2014) reviewed the studies: carbs that pass through several "gates" of the intestine, such as glucose plus fructose, are oxidized up to 75% more than carbs that use only one. This applies to a drink, a gel, or a bar. Check the ingredients, not the format.

The 120 g/h debate and training your gut

Should you aim for 120 g/h? Two recent studies give the context. In very well-trained cyclists (3 hours at 95% of their ventilatory threshold), 120 g/h burned more of the ingested carbs than 90 g/h, but it did not spare more of the body's glycogen (Podlogar and Wallis, 2022).

In elite male marathon runners, 120 g/h gave higher carb oxidation than 60 and 90 g/h, and a lower oxygen cost of running (2025 study, Journal of Applied Physiology). The authors note that the effect on performance still needs to be determined, and that nausea, bloating, and cramps were most frequent at 120 g/h.

Keep this in mind: 120 g/h is a research topic, not a target for your next run. No study yet proves it will make you run faster.

The same 2025 study concludes that targeted fueling during effort and training your digestive system are both justified. Studies show that digestive problems are common when the dose goes up. Coaching practice adds that you increase the dose gradually, run after run, the same way you increase volume.

To go further on the practical side, read Long run: how to tell if your fueling worked.

The day before a race and "train low"

For an event longer than 90 minutes, the Thomas et al. position statement suggests, if you want to supercompensate your stores, 10 to 12 g/kg per day for 36 to 48 hours before the start. The source is about events longer than 90 minutes. For a 10 km, that's not the point.

Another common idea is "train low" or "sleep low": training on purpose with few carbs so the body adapts. The meta-analysis by Gejl and Nybo (2021, 9 studies out of 407 articles) finds no overall effect on endurance performance compared with training on normal or high carbs. It covers trained athletes and few studies: this doesn't prove it's useless for everyone, but it doesn't justify cutting carbs to improve.

Eating too little: the real risk

In pursuit of lightness, some athletes eat less than their training load requires. In 2023, the IOC updated its consensus on this topic.

If you feel exhausted all the time, if your workouts get worse for no clear reason, or if you have doubts about your diet, talk to a doctor or a sports dietitian.

What you can do at your next workout

• ✓Identify your training load for the day: about 1 hour (5 to 7 g/kg) or 1 to 3 hours (6 to 10 g/kg).
• ✓Plan ahead what you will take during your long outings.
• ✓For efforts longer than 2.5 hours, aim for 60 to 90 g per hour, starting lower if your stomach isn't used to it.
• ✓Choose a product with glucose and fructose.
• ✓Write down how your stomach felt after the workout.

KILYO reads the workouts from your watch (Garmin, Apple Watch, Coros, Polar, Suunto, Strava), analyzes volume, pace, and heart rate, then adjusts your training plan to your actual training load. Then it's up to you to apply the g/kg guidelines to the heaviest days of your week.

Written with the help of AI.