In 30 seconds
- Taking carbohydrates during exercise improves performance: 82% of 61 studies found an improvement compared with water.
- The longer the effort, the greater the benefit and the more carbohydrates you need: up to 30 g per hour for 1-2 hours, up to 60 g for 2-3 hours and up to 90 g for longer events.
- Above 60 g per hour, glucose and fructose need to be combined: in one study, the time trial was 8% faster than with glucose alone.
- For efforts of less than 30 minutes they are not needed.
If you go out for a three-hour ride with only water, the last hour usually feels endless. The carbohydrates you take while you train are among the most studied topics in sports nutrition, and the conclusions are fairly clear.
Systematic review
Carbohydrates while you train: what one review gathered
Why they help
Your muscles store carbohydrates in the form of glycogen, but the store is limited. During long efforts it gradually empties, and when it gets very low, your pace drops. Taking carbohydrates during exercise provides extra fuel and spares that store.
In short, intense efforts something different happens: receptors in the mouth detect carbohydrates and activate areas of the brain linked to effort. That is why, in events of less than an hour, small amounts are enough, and even rinsing your mouth can help 1 2.
Level of evidence by outcome
| Outcome | Evidence | What the data show |
|---|---|---|
| Efforts of more than 2 hours | High | Clear improvement; the benefit grows with duration. |
| Efforts of 1 to 2 hours | High | Improvement in most studies with moderate amounts. |
| Efforts of 30 to 75 minutes | Moderate | Small amounts or even rinsing the mouth may help. |
| Glucose and fructose mix | Moderate | Allows more carbohydrate to be absorbed per hour in long events. |
| Less than 30 minutes | No effect | Does not improve performance. |
The rating is our own, based on the number of studies, their quality and the consistency of the results.
The key studies
| Study | Type | Sample | Outcome |
|---|---|---|---|
| Stellingwerff and Cox, 2014 | Systematic review | 61 studies, 679 people | 82% found an improvement compared with placebo. The longer the exercise, the greater the benefit. 1 |
| Jeukendrup, 2014 | Review | Recommendations | Amount according to duration: up to 30, 60 and 90 g per hour. Above 60 g, a mix of sugars. 2 |
| Currell and Jeukendrup, 2008 | Crossover trial | 8 trained cyclists | After 2 hours of cycling, time trial 8% faster with glucose and fructose than with glucose alone, and 19% faster than with water. 3 |
By duration of the effort
Maximum carbohydrates per hour
How many carbohydrates according to duration
The Stellingwerff and Cox review, with 61 studies, found that the benefit grows the longer the exercise lasts 1. Current recommendations adjust the amount to the duration 2:
| Duration | Carbohydrates per hour | Which type |
|---|---|---|
| Less than 30 min | Not needed | — |
| 30-75 min | Small amounts or a mouth rinse | Any |
| 1-2 hours | Up to 30 g | Glucose, sucrose or maltodextrin |
| 2-3 hours | Up to 60 g | Glucose, sucrose or maltodextrin |
| More than 2.5 hours | Up to 90 g | Glucose and fructose mix |
Source: Jeukendrup, 2014. At low intensities, the amounts may be smaller.
These amounts do not depend on your body weight, but they do depend on intensity: if you go easy, you use fewer carbohydrates and need less 2.
In long events
Glucose alone or glucose with fructose
Why mix glucose and fructose
The gut absorbs glucose through a pathway that becomes saturated at around 60 g per hour. Fructose enters through a different one, so by combining the two more can be absorbed 2.
In the Currell and Jeukendrup study, eight cyclists rode for 2 hours and then did a time trial. With glucose and fructose they were 8% faster than with glucose alone, and 19% faster than with water 3. The Stellingwerff and Cox review also concludes that the mix helps in long efforts 1.
How to put it into practice
- Start early: from the first half hour, in small, frequent amounts.
- Train your stomach: high amounts are better tolerated with practice. Try them in training, never for the first time on the day of the event 2.
- Combine formats: drinks, gels or solid food. A drink has the advantage of also providing fluid and sodium.
- Adjust to your tolerance: if you notice discomfort, reduce the amount or the concentration.
What about Nitrus?
Nitrus Isotonic provides 15 g of carbohydrates per serving of three types: fructose, dextrose (glucose) and maltodextrin. Dissolved in 400-500 ml, it gives between 30 and 38 g of carbohydrates per litre, around 130-165 kcal per litre, within the 80-350 kcal range that the EU Scientific Committee on Food recommends for sports drinks 4.
With one serving per hour you reach 15 g. For the 30 g of a 1-2 hour session, top it up with a gel, a piece of fruit or a second serving if you sweat a lot. And in longer events, add food or gels until you reach the amount you need.
Frequently asked questions
How many grams of carbohydrates should you take per hour?
It depends on how long the effort lasts: up to 30 g per hour between 1 and 2 hours, up to 60 g between 2 and 3 hours and up to 90 g in events lasting more than two and a half hours. For less than 30 minutes they are not needed.
Why mix glucose and fructose?
Because the gut absorbs them through different pathways. The glucose pathway becomes saturated at around 60 g per hour; adding fructose allows more to be absorbed without overloading it, and there is usually less stomach discomfort.
Does rinsing your mouth with a sugary drink work?
In hard efforts of 30 to 75 minutes, it can help. Receptors in the mouth detect carbohydrates and activate areas of the brain linked to reward and effort, even if you do not swallow them.
Gel, drink or food?
All three work if they provide the amount you need. A drink has the advantage of also replacing fluid and sodium. Always test your strategy in training, never on the day of the event.
Sources
- Stellingwerff T, Cox GR. Systematic review: carbohydrate supplementation on exercise performance or capacity of varying durations. Appl Physiol Nutr Metab. 2014;39(9):998-1011. View publication
- Jeukendrup AE. A step towards personalized sports nutrition: carbohydrate intake during exercise. Sports Med. 2014;44(Suppl 1):S25-S33. View publication
- Currell K, Jeukendrup AE. Superior endurance performance with ingestion of multiple transportable carbohydrates. Med Sci Sports Exerc. 2008;40(2):275-281. View publication
- Scientific Committee on Food (SCF). Report on composition and specification of food intended to meet the expenditure of intense muscular effort, especially for sportsmen. European Commission, 2001. View publication
Information based on published studies. It does not replace the advice of a doctor or registered dietitian. The results describe what was measured in each study, not the properties of any specific product. A varied and balanced diet and a healthy lifestyle are important.
