Carbohydrate intake during exercise can enhance endurance exercise performance. But some practical questions like: what is the best pattern of intake? have not been addressed.

Carbohydrate intake during exercise can enhance endurance exercise performance. This is one of the most well studied and established scientific findings in the sports nutrition literature. We discussed some of the background and current recommendations previously. These recommendations are to consume 30-60 g/h carbohydrate for events lasting 1 - 2.5 h and for events over 2.5 h up to 90 g/h. If more than 60g/h is ingested it is important to realise that the type of carbohydrate that is ingested is critically important. With these large amounts, a combination of carbohydrates, for example glucose and fructose, needs to be ingested.

Recommendations for carbohydrate intake

Current guidelines are pretty detailed, but usually not much attention was given but there is no specific advice on timing of intake. This was partly because early studies suggested that all carbohydrate ended up in the stomach and gastric emptying would gradually supply the intestine with carbohydrate. It was recommended to start the exercise with a good volume in the stomach (but without causing gastrointestinal problems), as it is known that the volume in the stomach is one of the main factors that will determine the speed of gastric emptying. A larger volume will empty faster than a smaller volume. But because everything ends up in the stomach, released to the intestine and the intestine then regulates the supply of carbohydrates, it was thought that the timing was not that important.

Large volume

The recommendation of a large volume in the stomach, is not ideal for runners. Runners cant usually drink large volumes during races as the fluids would be slushing around in their stomach and intestines. Runners usually take a few sips of a carbohydrate solution as they rush past the feed stations.

New study

Recently Steve Mears and colleagues at Loughborough University (1) investigated whether the pattern of carbohydrate sports drink ingestion during prolonged running, affects exogenous carbohydrate oxidation rates and gastrointestinal (GI) comfort. They asked runners to complete two 100 min steady state runs on a treadmill at a moderate intensity.

Once the runners consumed 200 mL every 20 min (CHO-20) and once they consumed 50 mL every 5 min (CHO-5). They found that exogenous carbohydrate oxidation rates were 23% higher during exercise when larger volumes were ingested every 20 min (0.38 ± 0.11

vs. 0.31 ± 0.11 g/min). It therefore seems that ingesting larger volumes would be better than frequently sipping smaller amounts.

Explanation

The explanation is likely that the larger volume will stimulate gastric emptying and makes more carbohydrate available for intestinal absorption. Therefore, the strategy that many runners use (small sips at all feed stations) may not be the preferred method. It may be better to make sure there is more fluid in the stomach. In the study by Steve Mears there was no difference in gastro-intestinal problems and this is also what we have observed in earlier studies. Runners may be able to tolerate much more than they think they can. When we gave 3 gels per hour to runners who were running at high intensity during 10 mile (16km) runs (2), we saw minimal gastro-intestinal problems even though we as researchers and the runners themselves were expecting a lot of GI issues with that high intake of carbohydrate! There is certainly a case to be made to take in more carbohydrate and practice this regularly in training to make sure no gastro-intestinal problems will develop and the gut adapts to this practice (read more in Training the gut)

References

1. Mears et al Sports Drink Intake Pattern Affects Exogenous Carbohydrate Oxidation during Running MSSE In press 2020

2. Pfeiffer, B., et al. (2009). "The effect of carbohydrate gels on gastrointestinal tolerance during a 16-km run." Int J Sport Nutr Exerc Metab 19(5): 485-503.