Not sure how much carbs to consume before, during and after exercise? With so much noise around low-carbohydrate and ketogenic diets, its easy to get confused as to how much carbohydrate you really need. Here’s a summary of the current carbohydrate recommendations for fuelling your body.
This is an abridged extract from The Complete Guide to Sports Nutrition (9th edition)
Why is carbohydrate important for performance?
Carbohydrate is the preferred fuel source for the brain, nervous system and heart and is used by the muscles to fuel both aerobic and anaerobic activities. Carbohydrate offers advantages over fat as a fuel since it provides more energy per volume of oxygen. It is, therefore, considered a more efficient fuel and is the fastest way for your body to produce energy.
Any glucose that’s not needed immediately for energy is converted to glycogen, which is stored in the cells of the liver and muscles. The liver can store a maximum of 100g of glycogen and the muscles a maximum of 400g, equivalent to a total of 500g or 2000 kcal worth of energy in an average person. This is relatively small compared to your fat stores. Most people have 90 – 120 minutes’ worth of glycogen they can use when doing high-intensity aerobic exercise. When glycogen stores are depleted fatigue sets in and you will need to reduce your intensity.
During exercise, glycogen is broken down into glucose and delivered to the muscle for energy. You’ll burn a mixture of fat and carbohydrate, but the more intense your workout, the more your body relies on carbohydrate for fuel.
The exact amount of carbohydrate you need to consume depends on the goals of your workout. When you want to maximise your performance, i.e. do high intensity training, daily carbohydrate intakes should match the fuel needs of training and glycogen replenishment. In this scenario, the following recommendations are appropriate:
|Activity level||Recommended daily carbohydrate intake (g/ kg body weight)|
|Very light training (low-intensity or skill-based exercise)||3–5 g|
|Moderate-intensity training (approx. 1 h daily)||5–7 g|
|Moderate–high-intensity training (1–3 h daily)||6–10 g|
|Very high-intensity training (>4 h daily)||8–12 g|
Your pre-exercise meal should provide 1–4 g carbohydrate per kg body weight, depending on exercise intensity and duration, and should be consumed between 1 and 4 hours before exercise.
Exercise < 45 minutes
If you’re exercising for less than 45 minutes, there is no performance advantage to be gained by consuming additional carbohydrates.
Exercise 45 – 75 minutes
When you’re doing high-intensity exercise lasting between 45 and 75 minutes, simply swilling (not swallowing) a carbohydrate drink in your mouth (‘mouth rinsing’) may improve performance. The carbohydrates stimulate oral sensors that act on the central nervous system (brain) to mask fatigue and reduce perceived exertion, thus allowing you to maintain exercise intensity for longer.
Exercise > 60 minutes
But for exercise lasting longer than about 60 minutes, consuming carbohydrate will help maintain your blood glucose level, delay fatigue and enhance your performance. The consensus recommendation is an intake of 30–60 g carbohydrate/hour, depending on the exercise intensity and duration. For low-moderate intensities, 30g/ hour is probably enough.
Exercise > 2 ½ hours
Previously, it was thought that the body could absorb no more than 60 g carbohydrate per hour. However, this relates to single source carbohydrates, such as glucose. Newer research suggests that it is possible to absorb more than this amount, as much as 90 g, if this comes from multiple transportable carbohydrate sources(e.g. glucose and fructose). A 2:1 mixture of glucose + fructose is less likely to cause gut problems than single carb sources.
|Exercise duration||Recommended amount of carbohydrate||Type of carbohydrate|
|< 45 minutes||None||None|
|45–75 minutes||Very small amounts (mouth rinse)||Any|
|1–2.5 hours||30 – 60 g/h||Any|
|> 2.5 hours||Up to 90 g/h||Multiple transportable carbohydrates (glucose or maltodextrin + fructose)|
Foods and drinks providing 30g carbohydrate
- One large banana (150g)
- 500 ml isotonic sports drink (6 g carbohydrate/100 ml)
- Two (40 g) Medjool dates
- 2 x 35g fruit and nut bars
- One (45g) energy bar
- One (50 g) energy gel
If you plan to train again within 8 hours, it is important to begin refuelling as soon as possible after exercise. To promote rapid post-exercise recovery, aim to consume 1.0–1.2 g carbohydrate/ kg BW/ hour for the first 4 hours after exercise. Moderate and high glycaemic index (GI) carbohydrates will promote faster recovery during this period. When carbohydrate intake is suboptimal for refuelling, adding protein to a meal/snack will enhance glycogen storage. However, for recovery periods of 24 hours or longer, the type and timing of carbohydrate intake is less critical, although you should choose nutrient-dense sources wherever possible.
Should you go low carb?
The concept of ‘training low but competing high’ as well as ‘carbohydrate periodisation’ (integrating short periods of ‘training low’ into the training programme) has become very popular among elite endurance athletes. Strategies include occasional fasted training, training following an overnight fast, and not replenishing carbohydrate stores after the first of two training sessions of the day.
Training in a glycogen-depleted state may amplify the adaptive responses to endurance exercise, such as mitochondrial biogenesis, and increase the muscles’ ability to use fat for fuel. However, there are drawbacks: exercise feels harder and results inevitably in a reduction in training intensity. For this reason, it is important to undertake high-intensity training sessions with high carbohydrate stores.
Chronically training with low glycogen stores can impair the muscles’ ability to store and use carbohydrate during high-intensity exercise. Another disadvantage of repeatedly ‘training low’ is the risk of illness, injury and over-reaching (short-term overtraining).
Despite increasing the muscles’ ability to use fat as an energy source, there is no clear evidence to date that chronically consuming a low-carbohydrate or ketogenic diet enhances endurance performance.
The Complete Guide to Sports Nutrition, ninth edition is the definitive practical handbook for anyone wanting a performance advantage. This fully updated and revised edition includes guidance on:
- maximising endurance, strength, performance and recovery
- the most popular sports supplements
- relative energy deficiency in sport (RED-S)
- hydration strategies
- nutrition for masters athletes, young athletes and plant-based athletes
- nutrition preparation for competition
- gut health and how to avoid gut problems during exercise