An ideal breakfast before a race

Asker Jeukendrup’s point of view

A fair amount of thinking goes into the breakfast before an important race. Advice has changed over the years and this is related to studies I will discuss here.
My view is that breakfast is highly individual and thus needs to be personalized. There is no one size fits all. But, what is best also depends on the duration and intensity of exercise, whether an athlete is prone to develop gastro-intestinal distress and several other factors.

Carbohydrate: studie’s in the 1970s

Sometimes you still read the advice to avoid carbohydrate  in the hour before exercise and others will tell you that you need it to improve performance. The reason for these different views stems from a couple of studies in the 1970s.

In those studies it was observed that eating carbohydrate in the hour before exercise resulted in high blood glucose and insulin concentrations 45 min after ingestion. Something that is indeed common knowledge now.

When the exercise was started blood glucose levels dropped rapidly because of a combined effect of high insulin levels and exercise on glucose uptake. In fact, blood glucose dropped so much that hypoglycemia (low blood sugar) occurred. This is often called rebound hypoglycemia or reactive hypoglycemia and is associated with symptoms of weakness, nausea and dizziness. It is also often assumed that hypoglycaemia will have a negative impact on performance. One of the early studies also reported that performance was reduced when carbohydrate was ingested before exercise compared with placebo (water) ingestion. The theory sounds great, but unfortunately as a result this study received way more attention than it should have.



Carbohydrates and performance: over a hundred studies

Since then, numerous (well over 100) studies have been performed with slightly different experimental designs. Generally these studies found either no effect or improved performance but the original findings of reduced performance were not confirmed!


The large numbers of studies were not easy to interpret because they were all different in their experimental designs. Some of these studies investigated carbohydrates that do not result in a large insulin response (low glycemic index carbohydrates) such as fructose. Others used glucose (higher insulin response) or other high glycemic index carbohydrates.


In addition to different types of carbohydrates, these studies used a variety of modes and intensities of exercise, and participants had different training backgrounds; some trained, some untrained were used. This made it very difficult to compare the results and very difficult to find out exactly what caused the different effects.


However, these studies (over a hundred from different research groups all over the world) showed almost all either no effect of carbohydrate feeding on performance or a positive effect. Unfortunately it was difficult to extract any meaningful advice from the roughly 100 studies with respect to the optimal amount and type of carbohydrate as well as the timing of intake.

Effects of carbohydrates before exercise

Therefore, we performed a series of studies in which we investigated the effects of pre-exercise carbohydrate feedings very systematically. All studies had a similar design and we only changed one variable at a time. The overall conclusion of these studies was that there was no effect on performance despite the fact that in some cases hypoglycemia did develop. There was no relation at all between the blood glucose levels and performance.

Hypoglycemia occurred more often when smaller amounts of carbohydrate were ingested (25 g) compared with larger amounts (75 g or 200 g) 45 min before the start of exercise.

Hypoglycemia was less prevalent when it is ingested just (15 min) before exercise compared with 45 and 75 min before. Low glycemic index carbohydrates did not cause hypoglycaemia (but are more likely to cause stomach problems).


An interesting finding was that some individuals developed hypoglycemia 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. Somewhat surprisingly this was not linked to insulin sensitivity of the individual.

In summary

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 of developing reactive hypoglycemia can find solutions to avoid it.


These solutions could include choosing low glycemic index carbohydrates, ingesting carbohydrate just before exercise or during a warm up or avoiding carbohydrate in the 90 min before. Every individual is different and therefore every athlete will need to develop their own pre-exercise routine that works best for him/her. If the exercise is longer and more intense (Ironman 70.3, Ironman), it is important to have a larger breakfast containing 200-300 g of carbohydrate.


If the exercise is shorter, or less intense a smaller breakfast with 100 g of carbohydrate may be enough. If the breakfast is larger, it is best to have it 3-4 hours before, if it is smaller it is ok to have it 2 hours before.


Jeukendrup AE, Killer SC. The myths surrounding pre-exercise carbohydrate feeding. Ann Nutr Metab. 2010;57 Suppl 2:18-25.

Professor Asker Jeukendrup is one of the world’s leading sports nutritionists/ exercise physiologists who spent most of his career as a professor at the University of Birmingham (UK). Dr Jeukendrup authored 8 books and over 200 research papers and book chapters. His expertise stretches from exercise metabolism and sports nutrition to training and overtraining. He is currently a (visiting) professor at Loughborough University and director of his own performance consulting business “Mysportscience” and communicates science through the popular website Asker works as Performance Manager for the Dutch Olympic team and is Head performance Nutrition for the Lotto Jumbo Pro cycling team. He also works with FC Barcelona, and other elite football clubs. Asker practices what he preaches and completed 21 Ironman races including 6 time the Ironman world Championship in Hawaii.