Article by Ruth McKean, Sports Nutritionist

Replacement during moderately intense exercise
(1 to 4 hours - Marathons, Triathlons, Cycling)

So why write an article on fluid and carbohydrate (CHO) replacement during exercise? And why should you read this?

Well, it has to be said that most athletes that take part in events that last longer than an hour do not maximise their fluid and carbohydrate (CHO) intake during exercise. This applies at both elite and club/recreational levels.

Yet it is an area that can improve your ability to maintain a certain level of intensity over a long training session or a race. By practising the correct and appropriate methods during training you'll help maximise training gains and, most likely, in a race situation it will all become second nature to you.

Choosing the right foods in the right amounts at the right time will not turn an average athlete into a world class athlete. However, a poor diet will prevent an athlete from realising their true potential.

The winter is always a good time to try out a change to fluid and eating plans in your training sessions. The following points are guidelines only and you should use these as a starting point to find out what works best for you.


It is now known that consuming Carbohydrates (CHO) and fluids during a race or a long training session will help you achieve a performance that reflects your training and natural ability.

Why Bother?

Carbohydrates can be stored as glycogen in both muscles (storing 300-400g of CHO) and liver (storing 100-150g of CHO). Glycogen is the energy source used by the muscles, but the muscle and liver stores are small compared to the 20kg or more that we have in fat storage. Athletes may be using as much as 3-4 g CHO per minute in a race, which quickly depletes the CHO stores in the body.


Athletes should aim to optimise their glycogen stores before exercise ("carbo-loading") as well as eating during exercise. This maximises the CHO availability in your blood which can be used by your working muscles. As a general guideline your intake of CHO should be between 30-60g per hour during a prolonged event. These CHO requirements can be met simultaneously with fluid needs by consuming CHO-electrolyte drinks. (See table at end for practical suggestions).

Remember CHO and fluid must be ingested well in advance of fatigue (approx. 30mins). Therefore, as a general rule, start drinking early and continue drinking throughout the event.

Other Reasons to Eat CHO
  1. Benefits for Immune System - There is evidence to suggest that consuming CHO during exercise is effective in reducing the rise of certain chemical substances (catecholamines and glucorticoids) which may be responsible of reducing the effectiveness of the immune system.
      • Researchers report a reduction in some of the minor immune infections (especially upper respiratory tract e.g. colds). While these are not serious infections, they can disrupt training and cause frustration.
      • If you are a regular cold sufferer, it might be worth consuming CHO during exercise to reduce your susceptibility to illness.


  2. Benefits to Body's Energy Store Recovery - Another reason to consume CHO during exercise is that it may help increase recovery of muscle glycogen stores in the post exercise period.
      • This is especially important to those who undertake a second exercise bout (i.e. multi day events or intensive training periods).
      • This point is not critical to those are going to take a full day off or more between there next bout of exercise.

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Athletes on the whole do not drink enough , even if there is unlimited access to drinks. Some athletes are not tolerant of large volumes in their stomach, but over time most athletes can increase their tolerance levels and fluid intake levels.

As a general guideline you should be aiming to drink 600-1000ml per hour of exercise. Take in fluids frequently (every 15 minutes), drinking moderate to large (150-350ml) volumes of fluid if possible.

The composition of the drinks is also important. A high concentration of carbohydrate in a drink will reduce the amount of fluid that is available for absorption, but will increase the rate of CHO delivery. For examples, fresh orange (unless diluted) or coke are high CHO drinks and water must move into your intestine to dilute this high concentration solution. As a result, this temporarily exacerbates dehydration.

Be aware that your thirst mechanism is not very sensitive and will not simulate drinking until some dehydration has occurred. In other words, by the time you are thirsty it's beyond the time when you should have started drinking fluids. Therefore, choose a drink that you enjoy the taste as this will encourage you to consume it consistently. The addition of flavours (diluting juice) is perhaps a good idea.

Helpful Tips
  • Fresh orange and sugary drinks may be helpful in promoting glycogen stores after exercise.
  • A low CHO-electrolyte drink is probably the most effective in most triathlon situation 6-8% CHO
  • Failure to drink enough fluid during exercise may contribute to stomach/bowel problems during exercise.
  • It is relatively easy to estimate how much water you lose by weighing yourself before and after exercise. For every 1-kg lost, 1.5 litres of water should be consumed.

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  • Begin exercise in a well-hydrated state (frequent & large volumes of clear/pale straw colour urine)
  • Use a fluid plan that has been practised in training
  • Choose a drink, which is cool, tastes good and provides CHO (6-8%)
  • Begin ingesting fluid early in competition/ cycle and continue to drink regularly to maintain a high volume of fluid in your stomach to increase fluid availability (150-300ml every 15-20mins.)
  • Plan to ingest 30-60g of CHO per hour of exercise. Either in a drink or food or both.

(see table at end of this section)

One last point to consider, when choosing foods to be consumed during competition do not be preoccupied with total energy intake. If you are trying to lose weight and don't eat during training or competition (if intense or/and long duration), then you are doing so at the risk of decreasing your performance. It would be advisable to eat and drink to maximise your performance and concentrate on a healthy balanced diet on a daily basis.

Finally, remember that choosing suitable foods in the right amounts at the right time will not turn an average athlete into a world class athlete. However, it is true that a poor diet will prevent an athlete from realising their true potential!

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Practical Guide to Carbohydrate Values

Plan to consume 30-60g of CHO per hour of exercise

The table below should give you an idea of how much/what 50g of CHO looks like in food terms. You can mix different foods to try to reach your CHO intake goals during an event.


  • When checking foods for CHO content, most foods will tell you the value per 100g, even if foods weigh more or less than this.
  • Knowing the CHO content of every day foods to use in training is just as good and in some cases better then some special sports bars or products on the market.

Food /Drink
To provide
50g of CHO
Nutrigrain bar 2 bars May help prevent hunger during long events. Fluid needs separate attention
Jaffa cakes 5 cakes Low in fat and quickly absorbed. Fluids need independent attention.
Bagel 1 bagel Low in fat, high in CHO. Fluids need independent attention. Perhaps not convenience during prolonged running events.
Soft drink 500 ml Slowly absorbed due to CHO content. Low sodium. May temporarily increase problem of existing dehydration due to high sugar content.
Fruit juices 500 ml See comment for soft drink. May cause stomach problem due to high amount of fructose
Jam sandwich 2 thick slices & 4 tsp of jam Quickly absorbed. Avoid dairy spread (fat tends to be more slowly absorbed). Fluid needs independent attention.
Sport drinks (5-8% CHO) 600-1000ml Easiest and most effective method for providing fluid and CHO simultaneously.
Jelly beans 50g Fluids need independent attention. Large amounts may cause stomach problems.
Sport gel 2
dep. on make)
Good for a large fuel boost. Need to practice in training to avoid gastrointestinal discomfort. Does not help fluid requirements. Expensive but compact and convenient
Banana 3 medium bananas May help prevent hunger but more than one portion is needed to provide enough CHO. Fluids need independent attention.
Sports Bars
1-2 (depending on the brand)
Convenience and compact but often have unnecessary vitamins and added extras - no scientific evidence to show that they improve performance. Expensive. Some are also relatively high in fat. However, they are convenient. Fluid needs individual attention.
Raisins 75g May cause stomach problems due to fibre content. But small and compact packages available. Fluid needs individual attention.
Rice Krispies Squares - chewy marshmallows 3 ½ bars Large quality needed. Fluid needs individual attention.


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