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Spoonful of sugar improves performance in endurance sport

Sucrose-based drink more effective than one based on glucose

Ingrid Torjesen

Tuesday, 01 December 2015

Stirring a spoonful of table sugar into a bottle of water before a long-distance sporting event could improve performance, research* published in the journal the American Journal of Physiology - Endocrinology & Metabolism suggests.

Researchers at the University of Bath tested various sucrose- and glucose-based drinks to see how different carbohydrates could help prevent fatigue in long-distance cyclists. They found that ingesting carbohydrates in the form of either glucose or sucrose prevents the decline in liver glycogen 'carbohydrate stores' and can avert tiredness. However, sucrose ingestion does increase whole-body carbohydrate utilisation compared to glucose ingestion.

For the study, 14 cyclists completed two 3-h bouts of cycling at 50% of peak power output while ingesting either glucose or sucrose at a rate of 1.7 g/min (102 g/h). Four cyclists performed an additional third test in which only water was consumed for reference.

Following glucose and sucrose ingestion, liver glycogen levels did not show a significant decline following exercise (from 325±168 to 345±205 and 321±177 to 348±170 mmol/L, respectively) with no differences between treatments. Muscle glycogen concentrations declined (from 101±49 to 60±34 and 114±48 to 67±34 mmol/L, respectively), again with no differences between treatments.

However, whole-body carbohydrate utilisation was greater with sucrose (2.03±0.43 g/min) vs glucose ingestion (1.66±0.36 g/min). Both liver (from 454±33 to 283±82 mmol/L) and muscle (from 111±46 to 67±31 mmol/L) glycogen concentrations declined during exercise when only water was ingested.

Both sucrose - in the form of table sugar - and glucose are simple sugars. The major difference between them is that each sucrose molecule is made up of one glucose and one fructose molecule linked together and it appears that combining different sources of sugars improves the rate at which we can absorb these from the gut.

Although an increasing number of sports-performance drinks designed to provide energy during exercise now use sucrose, or mixtures of glucose and fructose, many still rely on glucose alone. The researchers warn that such glucose-only drinks could produce gut discomfort and suggest sucrose-based alternatives, or sugar in water, can help make exercise easier.

Lead researcher Dr Javier Gonzalez explained: "The carbohydrate stores in our liver are vitally important when it comes to endurance exercise as they help us to maintain a stable blood sugar level. However, whilst we have a relatively good understanding of the changes in our muscle carbohydrate stores with exercise and nutrition, we know very little about optimising liver carbohydrate stores during and after exercise.

"Our study showed that ingesting carbohydrates during exercise can prevent the depletion of carbohydrate stores in the liver but not in muscle. This may be one of the ways in which carbohydrate ingestion improves endurance performance.

"We also found that the exercise felt easier, and the gut comfort of the cyclists was better, when they ingested sucrose compared to glucose. This suggests that, when your goal is to maximise carbohydrate availability, sucrose is probably a better source of carbohydrate to ingest than glucose."

The researchers recommend that if your goal is optimal performance during exercise lasting over two and half hours then consume up to 90g of sugar per hour - diluted to 8g sugar per 100ml.

* Gonzalez JT, et al. Ingestion of Glucose or Sucrose Prevents Liver but not Muscle Glycogen Depletion During Prolonged Endurance-type Exercise in Trained Cyclists. American Journal of Physiology - Endocrinology & Metabolism. Published 20 October 2015. DOI: 10.1152/ajpendo.00376.2015

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