How relevant is the GI for athletes?
'The glycemic index can be a useful tool to help athletes select the right type of carbohydrates to consume both before and after exercise,’ says Dr Emma Stevenson. ‘Several studies have investigated the effect of changing the GI of carbohydrates eaten before exercise on substrate metabolism during prolonged endurance exercise. Studies have consistently reported that a low GI pre-exercise meal results in a better maintenance of blood glucose concentrations during exercise and a higher rate of fat oxidation. This is likely to result in reduced muscle glycogen utilization during prolonged exercise and possibly improve endurance performance. Eating high GI meals before exercise may result in plasma glucose concentrations peaking before the onset of exercise and then hypoglycemia occurring within the first 30 minutes of the exercise period. There is little data available on the effect of the GI of carbohydrates eaten before intermittent, power or strength related sports.'
'During recovery from exercise, muscle glycogen resynthesis is of high metabolic priority. The eating high GI carbohydrates after exercise increases plasma glucose and insulin concentrations and this facilitates muscle glycogen resynthesis. If however, you are exercising for weight loss purposes or are involved in weight restricted sports, low GI carbohydrates after exercise may be more beneficial as the lower glucose and insulin concentrations will not suppress fat.'
‘I have recently been diagnosed with celiac disease on top of diabetes. Any suggestions for foods that are both low GI and wheat-free foods?’
This is not as hard as you may think. If you like Asian food – Indian dahls, stir-fries with rice, sushi, noodles - you're in luck, because they are all low GI. Choose vermicelli noodles prepared from rice or mung beans and low GI rices such as basmati. Use sweet potato instead of potato, use all manner of vegetables without any regard for their GI. Choose fruits and dairy for their low GI. If you can tolerate dairy products, then take advantage of them for their universal low GI. If lactose intolerance is a problem, reach for live cultured yoghurts and lactose-hydrolysed milks. Even ice-cream can be enjoyed if you ingest a few drops of lactase enzyme first. Dietitian Kate Marsh, however says: 'people need to check the labels of yoghurts and ice-cream for gluten as many do contain wheat based thickeners.'
What’s the real deal on the GI of beer?
Beer has so little carbohydrate that it's difficult to test its GI. That's why we listed its GI and GL as 0 in earlier editions of the New Glucose Revolution series books. But eventually we decided that the valid way to test beer would be by comparing responses to a 10 g carbohydrate portion of beer (about 300 mL) with a 10 g carbohydrate portion of glucose (in GI testing a 50 g carbohydrate portion is normally used). In this test the GI came out as 66. The GL will be therefore be 66 x 10/100 = 6.6 (round up to 7).
‘I have diabetes, but I enjoy an occasional drink. Does the way a beer is brewed (ales, lagers, pilseners, stout etc.) have a significant impact on the final product and its sugar content?’
Generally, alcoholic beverages contain very little carbohydrate. Most wines and spirits contain virtually none; regular beer contains around 10 g carbohydrate per 12 fl oz can; stout around 14 g carbohydrate per 12 fl oz can while a light beer has from 3–7 grams of carbohydrate per serving (12 fl oz can). Compare this with 36 g carbohydrate in a can of regular (not diet) soft drink! So yes, a beer will raise your glucose levels but not excessively. And if you drink beer in large volumes (not a good idea really) then you could expect it to have a significant effect on blood glucose. Although we haven’t GI tested many brands of beer, there are some useful websites out there that will tell you how much carbohydrate there is in various brands. We use www.calorieking.com as a quick reference.
As for enjoying an occasional drink, researchers (Kaniz Fatima and Chris Middlemass) from the University of Sydney reported at the Nutrition Society of Australia (November 2005) that a pre-dinner drink tends to produce a ‘priming’ effect, flicking the switch from internal to external sources of fuel and keeping blood-sugar levels low. In one study, they gave healthy, young, lean people two standard glasses of beer, or wine, or gin and tonic or water to drink about an hour before eating a meal then they measured their blood glucose and insulin levels. They found that: ‘realistic amounts of beer, wine or gin reduce postprandial glycemia but not insulinemia’.
© ® & ™ The University of Sydney, Australia
2 April 2006
How relevant is the GI for athletes?
Posted by GI Group at 8:00 am