Eating and drinking on the run: how many carbs and how much water
When you need to eat while running, how many grams per hour depending on duration, why drinking to thirst is safer than drinking to a plan, and what to do before and after.
Under an hour, in-race nutrition is irrelevant for almost everyone. Beyond that, carbohydrates go from optional to deciding how you finish. And the stomach is trained just like the legs.
This is eating during, not eating per day
What follows is grams per hour of effort. How much to eat across the day —your expenditure, your protein and the split— is a different sum, and it lives in how many calories you need and planning the deficit or the surplus. For the number itself, the calorie calculator.
How many carbs per hour
The dose depends on the duration of the effort, not on body weight
The joint ACSM position stand and the landmark review on endurance nutrition agree on scaling by duration: ~30 g/h between 1 and 2 hours, up to 60 g/h between 2 and 3 hours, and up to 90 g/h beyond 2.5–3 hours using multiple transportable carbohydrates (glucose and fructose blends), which get past the intestinal absorption limit of glucose alone.
- < 60 min
- Nothing
- 1–2 h
- ~30 g/h
- 2–3 h
- 60 g/h
- > 2.5–3 h
- Up to 90 g/h
Your glycogen stores have you covered.
One gel or a sports drink per hour.
Two gels an hour, or gel + drink.
Only with glucose+fructose products and a trained stomach.
The stomach is trainable
Going from zero to 90 g/h on race day is the classic recipe for a gastrointestinal problem. Practise your intake on the long runs, with the same products and at the same intervals you will use in competition. Which product to buy, how they differ and what an hour of running costs, in supplements for running.
Drinking: to thirst
Drinking to thirst prevents practically all exercise-associated hyponatraemia
The 2017 update on exercise-associated hyponatraemia, following the international consensus conference, holds that the main cause is excess hypotonic fluid and that drinking in response to thirst avoids practically every case. Fixed-volume guidance is not appropriate because losses vary enormously between people and conditions.
In long races or in heat, add sodium (sports drink, capsules or salty food): the goal is not to avoid any weight loss at all, but to avoid diluting plasma sodium by drinking plain water. How much sodium, in what format, and when salt tablets add nothing, in supplements for running.
Before and after
- 1
The 24 h before
Nothing exotic. In events over 90 minutes, raising carbohydrate intake the day before makes sense; in a 10K it barely changes anything.
- 2
1–3 h before
A meal high in carbohydrate, low in fibre and fat, already tested in training. If you are up very early, something small and liquid works better.
- 3
Caffeine, if it agrees with you
It is one of the few ergogenic aids with solid support for endurance, around 3–6 mg/kg some 45–60 minutes before. Test it in training: it upsets some people’s stomachs.
- 4
Afterwards
Carbohydrate and protein in the first hour, especially if you are training again within 24 h. If you have all day to recover, it matters far less than people say.
Takeaways
- Under an hour: water and little else.
- Scale carbohydrate by duration: 30 → 60 → up to 90 g/h.
- Above 60 g/h, only glucose + fructose products.
- Drink to thirst; add sodium in long races or in heat.
- Rehearse the whole strategy on your long runs, never on race day.
Sources for this chapter
- [1]Thomas DT, Erdman KA, Burke LM (ACSM, AND, DC) (2016). Joint Position Statement: Nutrition and Athletic Performance. Medicine & Science in Sports & Exercise. position stand
- [2]Jeukendrup AE (2011). Nutrition for endurance sports: Marathon, triathlon, and road cycling. Journal of Sports Sciences. review
- [3]Hew-Butler T, Loi V, Pani A, Rosner MH (2017). Exercise-Associated Hyponatremia: 2017 Update. Frontiers in Medicine. review