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.
Carbohydrate recommendations
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)
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)
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
After exercise
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.
One of the most common questions I get asked by runners is how to fuel during long runs when you don’t feel like eating anything. Many find that drinking a sports drink or eating food makes them feel like throwing it straight back up. Do you also struggle fuelling during races? Well, you’re not alone – fuelling on the move can prove tricky for many. It can make you feel bloated, uncomfortable, queasy and even trigger vomiting or diarrhoea.
As result, many endurance athletes prefer training on ‘empty’, shunning fluid at aid stations and forgoing fuel during races for fear of unplanned toilet stops. But when you’re exercising at high intensities and competing for longer than 60 – 90 minutes, this strategy can quickly lead to dehydration, reduced endurance and perhaps not even finishing the race. Quite a conundrum.
Fortunately, there is a solution: ‘gut training’. Sports scientists say that the gut is very adaptable. This means that it can respond to nutritional training during exercise. In other words, you can literally train your gut – much like any other muscle in your body – to tolerate and absorb more carbohydrate while exercising. There’s not been a great deal of research on the topic but this excellent review by Asker Jeukendrup provides a neat summary.
What’s required is a gradual and consistent approach to fuelling and drinking on the move. The idea is to start with small quantities and increase slowly over time. With practice, your stomach will learn to accommodate a greater volume of fluid and food and empty faster so you start to feel less full and uncomfortable whilst exercising.
By focusing on carb-rich foods and drinks, you’ll also train your gut to absorb carbohydrates more efficiently. This increases the number and activity of glucose transporters in the gut, allowing greater carbohydrate absorption and utilisation during exercise.
Normally the gut can only absorb a maximum of 60g per hour. Any more than this just sits ‘heavy’ in the stomach. But by gradually increasing the amount of carbs you consume during exercise and by consuming a mixture of glucose (or maltodextrin) and fructose (such as an energy drink), you can train your gut to absorb up to 90g per hour. This would be beneficial when you’re exercising at high intensities for longer than 2 hours.
How long will it take to train your gut? Like most things in nutrition, it’s very individual. Some people adapt quicker than others but you can expect a significant improvement within a few weeks. Here’s how to train your gut for workouts longer than 60 – 90 minutes
Gradually increase the amount of fluid you consume during exercise – little and often works best. Start with just a couple of sips pre- and mid-workout, then increase gradually as you become accustomed to the sensation of fluid in your stomach.
Experiment with different food options to discover which foods or products your body can tolerate. Try a couple of bites of banana, a Medjool date, an energy ball (such as these Energy Balls) or a bite of energy bar. Other options include fruit bars, jelly babies, energy gels, plain biscuits, rice cakes or fig rolls.
Begin refuelling after 30 or 60 minutes, then aim for 10 – 15g carbs every 30 minutes. Do this for each long workout (> 90 minutes). Once this feels okay, up the quantity or add another mid-workout ‘feed’. Over time your stomach will learn to accept bigger volumes and empty faster, so instead of feeling full and bloated, you’ll feel comfortable.
When preparing for a big race, it’s important to practise your fuelling plan during training. Take the same foods and drinks that you plan to use in the race. It may take quite a bit of trial and error so try to do this early in your race preparation programme. Don’t leave it to race day!
Being able to train your gut this way will give you a huge advantage for training and races longer than two hours. It means that you’ll be able to stay fuelled, cut the risk of getting gut problems and ultimately improve your performance.
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Periodised carbohydrate training has become the latest buzzword among endurance athletes. Essentially it means matching your diet to your workload and new research suggests it may improve endurance performance and make you a more efficient fat burner.
The idea behind training with low glycogen stores (‘training low’) is that it forces the muscles to burn more fat for fuel and rely less on carbohydrate. By teaching your body to tap into its fat stores, you should in theory be able to keep exercising for longer before reaching fatigue.
Indeed, studies (here and here) have shown that when you ‘train low’ you increase the muscle’s adaptive response to training. It increases mitochondrial biogenesis, so you get an increase in the number and volume of mitochondria – the fat-burning powerhouses – in the muscle cells. The more mitochondria you possess, the greater your muscles’ ability to use fat as fuel, sparing your glycogen stores.
High-intensity exercise feels much harder. Your performance, rather than improving, may drop. Your immune system may become depressed, increasing the risk of infection. And you could lose muscle.
But with periodised carbohydrate training you get the dual benefits of ‘training low’ – namely fat adaptation – as well as the performance benefits of high intensity training. Also, it’s a more sustainable approach. Essentially, it means doing some of your low-intensity sessions in a carb-depleted state, and your higher intensity sessions with high glycogen stores.
The simplest way to ‘train low’ is to train in the morning before breakfast. However, this should be done before an easy session, nothing too long or too intense. Alternatively, if you want to train low in the evening, cut carbohydrate at breakfast and lunchtime (keeping to mainly high-protein foods and vegetables). Another method is ‘sleeping low’. This means doing a tough session before sleep, eating a low carb dinner then doing a low-intensity session the next morning.
This method looks more promising in terms of performance improvement. A multi-centre 2016 study with triathletes found that those who followed a ‘sleeping low’ protocol for three weeks improved their cycling efficiency (power output per calorie) by 11%, 10km running performance by 2.9%, time to exhaustion during high intensity exercise by 12.5%, and also reduced their body fat compared with those who did all their training with high glycogen stores.
A follow-up study with cyclists by the same team found that using a ‘sleeping low’ strategy for just six days resulted in a 3.2 percent improvement in a 20K time trial.
Most recently, a study at the Australian Institute of Sport compared the performance effects of a high-carb diet (60 – 65% carb), a periodised carb diet (same macro’s but periodised within or between days) and a LCHF diet (<50g carbs) in a group of 21 elite race-walkers. After 3-weeks on each diet, all athletes improved their aerobic fitness (VO2 max) but only those on the high carb or periodised carb diet improved their 10k race performance. The athletes on the LCHF diet did not make any improvement. Although they were burning a higher proportion of fat during exercise, their muscles became less efficient at producing energy, requiring more oxygen at any given speed. All of which suggests that fat adaptation incurs an efficiency penalty.
To date, this is the highest quality study on low carb vs high carb that we have. Although It makes a pretty damning case against chronic low carb diets, it also provides good evidence for a periodised carbohydrate approach.
In summary, eating low carb all the time is unlikely to benefit your performance unless you’re exercising at a relatively low intensity for long periods, such as ultra-distance events. For other endurance activities, it may be worth trying a periodised low carb approach.
Pick just one or two short low-intensity sessions a week alongside your normal training when you are fully fuelled. Keep a training log and see whether it helps your training or not. If you suffer gut problems when consuming carbs during running, then ‘training low’ may suit you. Also, not having to carry bars and gels during long runs may be helpful from a practical point of view. Remember, whatever the research says, a good nutrition strategy boils down to doing whatever works for you as an individual.
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More than 100 delicious, easy-to-prepare vegetarian and vegan recipes for healthy breakfasts, main meals, desserts, sweet and savoury snacks and shakes.
Expert advice on how to get the right nutrients to maximise your performance without meat
Stunning food photography
Full nutrition information for each recipe, including calories, carbohydrate, fat, protein and fibre
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:
If you’re looking for some easy and tasty inspiration on how to include more plant foods in your diet, then 
More than 100 delicious, easy-to-prepare vegetarian and vegan recipes for healthy breakfasts, main meals, desserts, sweet and savoury snacks and shakes.