Perspectives with Dr Alan Barclay

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Alan Barclay

Optimise Physical Performance with Low GI Carbs. 
For high intensity exercise that requires quick bursts of speed, like football, netball, basketball, marathons, etc., carbohydrate, or more specifically glucose, is the preferred fuel for your muscles. Consequently, eating enough carbohydrate at the right time in your training schedule, and before the event, has long been one of the key foci of nutrition advice. However, the role of the type or quality of carbohydrate in enhancing physical performance has not been clear.

Due to their slower rates of digestion, absorption and metabolism, low GI foods and meals provide a slow and sustained release of glucose, with a lower peak in blood glucose levels after a meal and correspondingly lower peak in insulin levels. The benefit of consuming low GI foods/meals prior to physical activity is that the resultant changes in blood glucose and insulin levels are not as rapid as what occurs when high GI foods/meals are consumed, so consequently consuming low GI foods/meals will lead to an increase in free fatty acid (blood fat) oxidation and more optimal maintenance of blood glucose levels, leading to more sustained glucose availability for working muscles. This means that consuming low GI foods/meals before an event should translate into improved physical performance.

In 2013, dietitians Talya Postelnik, Alan Barclay and statistician Peter Petocz set out to see if the body of scientific evidence supported this. They conducted a systematic literature review and found 15 studies in humans that met stringent selection criteria and were eligible for meta-analysis. When exercising to exhaustion, as may occur in many team sports or marathons, people that consumed a low GI food or meal between 0.5 and 3 hours before an event were able to keep going for an average of 22% longer. When participating in time trials, people that consumed the low GI food or meal were significantly quicker (3% improvement) than those that consumed the high GI foods/meals. So overall, the results do indicate that consuming low GI foods/meals before an event will lead to significant improvements in physical performance.


For optimal performance, it is important that you eat and drink foods and beverages that best suit your personal and cultural preferences, and the event you are participating in, so as always, see your Accredited/Registered Dietitian for personalised advice.

Alan Barclay (BSc; Grad Dip; PhD, APD, AN) is a consultant dietitian and Chief Scientific Officer at the Glycemic Index Foundation. He worked for Diabetes Australia (NSW) from 1998-2014 and is a member of the editorial boards of Diabetes Australia’s consumer magazine, Conquest, and health professional magazine, Diabetes Management Journal. He is coauthor of The Low GI Diet: Diabetes Handbook, The Low GI Diet: Managing Type 2 Diabetes, and The Ultimate Guide to Sugars and Sweeteners. Contact: