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Thursday, 2 February 2012

Carbohydrate Intake is Correlated to Finishing Times in Endurance Events

We all know that carbohydrate intake improves endurance performance. There is an overwhelming body of research that has demonstrated that carbohydrate ingestion before (i.e. carbo loading) and during enhances exercise performance.

Information on actual nutritional intake and gastrointestinal problems in endurance athletes competing in ultra-endurance events is lacking. Particularly events such as marathons, ironman races and professional bike races. To address this Pfeiffer and colleagues (2012) carried out a study to investigate nutritional intake and gastrointestinal problems during competitive endurance events.

Pfeiffer et al. (2012) recruited 221 male and female endurance athletes competing in ironman events, marathons, 100-150 km cycle races, and professional riders during stage races. Athletes completed a questionnaire that quantified nutritional intake and GI problems.

As you can see from the table below, carbohydrate intake varied greatly between among the individual athletes (as seen by the large SD values) and the different events.

In the two triathlon events (IM Hawaii and IM Germany) carbohydrate intake was highest on the bike leg (as expected) and reported intakes were similar to the recommended 90 g/hr of exercise as seen in the table below.

The most interesting finding was that higher carbohydrate intakes were significantly correlated with faster finishing times as seen below.

And finally, although high carbohydrate intakes were not associated with higher average scores for upper or lower GI distress, they did seem to be a risk factor for symptoms such as flatulence and nausea. It is important to note at this point that there is evidence that you can train the gut to tolerate high intakes of carbohydrate during a race (i.e. 90 g/hr). The type of carbohydrate is also important i.e. multiple transportable carbohydrates. In other words, carbohydrate that contains glucose AND fructose in a ratio of 2:1. If you are competing in endurance events, check that your carbohydrate gels/drinks/bars contain glucose and fructose.

So in conclusion, carbohydrate intake varies greatly amongst athletes and events and it is very individual. Although, higher carbohydrate intakes were associated with faster finishing times, they were also associated with greater symptoms of nausea and flatulence. Therefore the advice is that, everybody is different. An individualised carbohydrate strategy is needed and bear in mind that the gut can be trained to tolerate high intakes. Always try feeding strategies in training before you trial them in a race.

Mayur Ranchordas

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