As runners we are often bombarded with information on the importance of carbohydrate in our diets. From pre-race pasta parties, to the gels and carbohydrate drinks that we see advertised in magazines and in sports shops. Hopefully by the end of this article you will have a better idea of when, or even if to carb-load, how to go about it and what foods or drinks to choose.
Why runners may need to carb-load
Although we all need carbohydrate in our diets at each meal time, not all runners need to carb-load. We store a maximum of about three hours worth of carbohydrate in our muscles and liver as glycogen and, as we go about our daily lives, or indeed run, this glycogen is turned into sugar (glucose) and is used as our body's preferred fuel source.
Provided that we are taking in some carbohydrate at each meal time, we do not need extra carbohydrate during runs of less than 90 minutes. For these 'shorter' runs we also do not need to significantly increase our carbohydrate intake in the days before the run.
However, for runs over 90 minutes, runners may benefit from taking on some carbohydrate (usually in the form of gels or isotonic sports drinks) to top up carbohydrate stores and enable them to perform at their best, for longer. Increasing carbohydrate intake in the three to seven days before a long run such as a marathon, coinciding with the usual taper in training has also been shown to increase glycogen storage and therefore prolong the time that the runner can perform without 'hitting the wall', (a feeling of extreme weakness and often mental exhaustion in the latter stages of a marathon when glycogen stores are depleted).
Carb loading has been found to increase time to exhaustion by on average 20% It used to be the case that runners would precede this period of carb-loading with a depletion stage in order to enhance glycogen storage to a greater degree. However this had drawbacks including poor training, low blood sugar, gastro-intestinal problems such as diarrhoea, poor recovery, increased risk of injury and irritability, all of which would risk hindering performance, irrespective of the increased carbohydrate stores. The preferred method of increasing carbohydrate with a gradual taper over the last week, is therefore usually recommended as it results in nearly as much glycogen storage without the disadvantages.
How it works, what to eat (and when)
As with all training and dietary changes, it is important to have a trial run on less important races or on long training runs, to determine if it suits you. Some runners feel too full to run well after a few days on a higher carbohydrate intake and others dislike the inevitable fluid and therefore weight that they will carry when glycogen stores are increased.
If we continue to eat the same amount of carbohydrate in the week before a marathon as we have done in training, the reduced mileage in the tapering weeks will automatically mean that we are storing the excess carbohydrate that is not being used up. This is a form of carb-loading which many runners prefer to do as it allows them to stick to their usual, familiar dietary routine and can feel less alien to them.
When we carb-load by consciously eating more carbohydrate during the tapering week before a long run, we store the excess carbohydrate that we are not using up, as glycogen and, with this, we store fluid. This results in weight gain which can affect the runner's perceived effort on the run. It is therefore essential that any carb-loading strategy is trialled before the important race, on long training runs.
If you do want to try carb-loading, continue to eat your usual amount of carbohydrate at meal times as your mileage reduces. For an average 60kg female runner, this could be about two to three handfuls of bread, cereal, pasta, rice or potatoes at each meal. For 80kg male runner, this is likely to be nearer three to four handfuls at each meal. Then increase your carbohydrate intake by adding in three carbohydrate snacks between meals, perhaps as a morning, afternoon and evening snack.
Check out some of our other nutritional advice here