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Should I Eat or Drink in the Hour Before my Race?

Eating in the hour before was said to be detrimental to performance, but research shows otherwise.

There is a lot of mixed information when it comes to eating or drinking in the last hour before competition. Taking in some carbohydrate (see ‘What is a Carbohydrate?’) may help, because it provides extra fuel that may be needed, especially during longer events. However, it can also result in so called rebound hypoglycaemia or reactive hypoglycaemia with symptoms of weakness, dizziness and nausea. So, it can have positive as well as negative effects? What should we do? This blog will give you the ins and outs. The reason for these different views stems from a couple of early studies. In the 1970s, it was observed that consuming carbohydrate in the hour before exercise resulted in high blood glucose and insulin concentrations 45 minutes after ingestion. This is expected. Glucose is being absorbed and as glucose enters the circulation the blood glucose concentration rises. As a result of this, insulin is released to make sure the blood glucose concentration in the blood is normalised. It does this by increasing the glucose uptake in muscle and other tissues. This way, at least in healthy individuals, the blood glucose concentration is very tightly controlled in a relatively narrow range.


Should I Eat or Drink in the Hour Before My Race Infographic



What is Rebound Hypoglycaemia?

45 minutes after ingestion of a load of carbohydrate, insulin will be high and uptake into different tissues will be high. And if at that point exercise is started, the muscle will start to take up even more glucose from the blood. The result is that glucose is disappearing from the blood faster than it is entering the blood and a rapid drop of the blood glucose levels can often be observed (see infographic). The blood glucose concentrations drop so much that hypoglycaemia can occur. Hypoglycaemia means that blood glucose has dropped below a certain level. This low blood glucose level is usually associated with a number of symptoms such as weakness, nausea and dizziness and sometimes cold sweat and shaking of the hands. In the 1970s they assumed that low blood glucose would not be desirable for performance and thus the recommendation was made to avoid all carbohydrate in the hour before exercise. Now, many years later, we know a little more about the intricacies and the advice is more precise. A low blood glucose level is usually associated with symptoms such as weakness, nausea, dizziness, cold sweat and shaking of the hands.


Effects on Performance

One of the early studies did indeed report that performance was reduced when carbohydrate was ingested before exercise compared with placebo (water) ingestion. However, since then, almost all studies have shown either no effect on performance or a positive effect, if carbohydrate was ingested during exercise. This is despite the fact that most studies showed a drop in blood glucose. So, it seems that a drop in blood glucose does not necessarily affect performance, and also that the magnitude of this drop may depend on the exercise intensity, the type of carbohydrate ingested, the amount that is ingested as well as the timing of ingestion.


What is the best carbohydrate?

There are many different types of carbohydrate and they can have different effects (see article entitled "What is a Carbohydrate?" or "Not All Carbs are Equal."). Some carbohydrates do not result in a large insulin response (low glycemic index carbohydrates). Fructose is an example, galactose is another. Other carbohydrates like glucose or maltodextrin (high glycemic index carbohydrates) will have a greater insulin response. Unfortunately, lower glycemic index carbohydrates deliver energy slower, remain in the gastro-intestinal tract longer and can increase gastrointestinal issues.


How much carbohydrate?

A drop in blood glucose can be prevented in two ways: the first one to take the last meal long enough before exercise (>1.5 hours) or to ingest a small amount of carbohydrate (such as 1 x C30 Energy Gel) 10 minutes or so before the start of exercise. The last advice seems the most desirable. The carbohydrate ingested just before will become available during exercise and the muscle can use it as a fuel. During exercise insulin levels will not rise (or not rise as much) because adrenaline will reduce insulin. So, with the right timing it is possible to deliver carbohydrate and not cause rebound hypoglycaemia.


Individual differences

An interesting finding from one of our studies was that some individuals developed hypoglycaemia in all conditions, whereas others never developed it. This observation is in line with some athletes reporting to be very sensitive to carbohydrate feedings and others who can eat whatever they want and never get symptoms of hypoglycaemia. There are also large individual responses of different athletes to the same carbohydrate intake. Therefore, in addition to following the general recommendations here, it is important to fine tune this at an individual level and work out what works best for you.

It is important to fine-tune carb feedings at any individual level and work out what’s best for you.


Caffeine intake

Another consideration in the hour before the start is the intake of caffeine. Caffeine whether is through coffee, caffeinated gels such as C30+ Energy Gels, liquid caffeine ‘shots’ or pills, takes 30 to 60 minutes to reach a peak concentration in the blood. Caffeine can reduce the perception of effort and improve performance and therefore many athletes take caffeine before competition. For longer events (> 3 hours) it may be wise to take caffeine a little later during the race or to spread caffeine intake. For shorter events, especially events of 1 to 2 hours it is recommended to take it in the hour before. More about caffeine intake, dosing, different sources and individual responses can be found in this article on: How to take caffeine.


So, what does all this mean for me?

In practical terms, this means that it is ok to consume carbohydrate before exercise as there do not seem to be any detrimental effects on performance. Individuals prone to developing reactive hypoglycaemia can find solutions to avoid it. Perhaps the best way to do this is to ingest carbohydrate 5 to 10 minutes before the start of exercise (the amount depends on comfort and also the duration and intensity of the activity). Although this can serve as a starting point, it is important to realise that responses can be highly individual and therefore every athlete will need to dial in their own pre-exercise routine that works best for you.


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  • Jeukendrup AE, Killer SC. The myths surrounding pre-exercise carbohydrate feeding. Ann Nutr Metab. 57 Suppl 2:18-25, 2010.
  • Achten J, Jeukendrup AE. The effect of pre-exercise carbohydrate feedings on the intensity that elicits maximal fat oxidation. J Sports Sci 21(12): 1017-1024, 2003.
  • Achten J, Jeukendrup AE. Effects of pre-exercise ingestion of carbohydrate on glycaemic and insulinaemic responses during subsequent exercise at differing intensities. Eur J Appl Physiol 88(4-5): 466-471, 2003.
  • Jentjens, RL. and Jeukendrup AE. Effects of pre-exercise ingestion of trehalose, galactose and glucose on subsequent metabolism and cycling performance. Eur J Appl Physiol 88(4-5): 459-465, 2003.



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