Glycaemic Index
Burke, L. M., G. R. Collier, and M. Hargreaves. Glycemic index - a new tool in sport nutrition? International Journal of Sport Nutrition 8: 401-415, 1998.
Burke, L. M., A. Claassen, J. A. Hawley, and T. D. Noakes. Carbohydrate intake during prolonged cycling minimizes effect of glycemic index of preexercise meal. Journal of Applied Physiology 85: 2220-2226, 1998.
Burke, L. Pre-Event meals: high or low glycemic index foods? Sportscience News May-Jun 1998. http://www.sportsci.org/news/compeat/glycemic.html
Burke, L. Carbohydrates? They aren't that simple! Sportscience News Sep-Oct 1997.
http://www.sportsci.org/news/compeat/carbo.htm
Burke L. M., G. R. Collier, and M. Hargreaves. Muscle glycogen storage after prolonged exercise: effect of the glycemic index of carbohydrate feedings. Journal of Applied Physiology 75: 1019-1023, 1993.
Burke, L. M., G. R. Collier, and M. Hargreaves. Glycemic index - a new tool in sport nutrition? International Journal of Sport Nutrition 8: 401-415, 1998.
The glycemic index (GI) provides a way to rank foods rich in carbohydrate (CHO) according to the glucose response following their intake. Consumption of low-GI CHO foods may attenuate the insulin-mediated metabolic disturbances associated with CHO intake in the hours prior to exercise, better maintaining CHO availability. However, there is insufficient evidence that athletes who consume a low-GI CHO-rich meal prior to a prolonged event will gain clear performance benefits. The ingestion of CHO during prolonged exercise promotes CHO availability and enhances endurance and performance, and athletes usually chose CHO-rich foods and drinks of moderate to high GI to achieve this goal. Moderate- and high-GI CHO choices appear to enhance glycogen storage after exercise compared with low GI CHO-rich foods. However, the reason for this is not clear. A number of attributes of CHO-rich foods may be of value to the athlete including the nutritional value of the food or practical issues such as palatability, portability, cost gastric comfort, or ease of preparation.
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Burke, L. M., A. Claassen, J. A. Hawley, and T. D. Noakes. Carbohydrate intake during prolonged cycling minimizes effect of glycemic index of preexercise meal. Journal of Applied Physiology 85: 2220-2226, 1998.
We studied the effects of the glycemic index (GI) of preexercise meals on metabolism and performance when carbohydrate (CHO) was ingested throughout exercise. Six well-trained cyclists performed three counterbalanced trials of 2-h cycling at approximately 70% of maximal oxygen uptake, followed by a performance ride of 300 kJ. Meals consumed 2 h before exercise consisted of 2 g CHO/kg body mass of either high-GI potato (HGI trial) or low-GI pasta (LGI trial), or of a low-energy jelly (Con trial). Immediately before and throughout exercise, subjects ingested a 10 g/100 ml [U-14C]glucose solution for a total of 24 ml/kg body mass. Despite differences in preexercise glucose, insulin, and free fatty acids concentrations among trials, both total CHO oxidation for HGI, LGI, and Con trials, respectively, during steady-state exercise [403 +/- 16, 376 +/- 29, and 373 +/- 24 (SE) g/2 h] and oxidation of the ingested CHO (65 +/- 6, 57 +/- 6, and 63 +/- 5 g/2 h) were similar. There was no difference in time to complete the subsequent performance ride (946 +/- 23, 954 +/- 35, and 970 +/- 26 s for HGI, LGI, and Con trials, respectively). When CHO is ingested during exercise in amounts presently recommended by sports nutrition guidelines, preexercise CHO intake has little effect on metabolism or on subsequent performance during prolonged cycling (approximately 2.5 h).
Order full article via the NSIC
Burke, L. Pre-Event meals: high or low glycemic index foods? Sportscience News May-Jun 1998.
http://www.sportsci.org/news/compeat/glycemic.html
Athletes have been cautioned that eating carbohydrate foods in the hour before exercise may alter exercise metabolism by stimulating insulin production, which in turn increases the rate at which the muscles burn carbohydrate. As a result of this faster rate of carbohydrate oxidation, blood glucose levels may actually fall (a condition known as hypoglycemia) shortly after exercise begins. In most cases this effect is short term, and metabolism corrects itself as exercise continues. The occasional athlete experiences impaired performance, and it has been found in one study. But mostly there are no problems, and in some situations pre-exercise carbohydrate can even improve exercise performance. Nevertheless, the stigma about athletes eating carbohydrate before exercise persists, and many athletes and coaches talk about "rebound hypoglycemia" with fear, even though eating carbohydrate could potentially provide extra fuel during a prolonged training session or race.
Burke, L. Carbohydrates? They aren't that simple! Sportscience News Sep-Oct 1997.
http://www.sportsci.org/news/compeat/carbo.htm
Nutritionists like me have succeeded in convincing athletes to think of carbohydrates as their best fuel source. What they may not recognize is that carbohydrates cannot be lumped into one category. Most athletes have even heard that there are simple and complex carbohydrates. However, pardon the pun, carbohydrates are more complex than that. When it comes to planning their training meals, athletes need to understand and use the glycemic index.
Burke L. M., G. R. Collier, and M. Hargreaves. Muscle glycogen storage after prolonged exercise: effect of the glycemic index of carbohydrate feedings. Journal of Applied Physiology 75: 1019-1023, 1993.
The effect of the glycemic index (GI) of postexercise carbohydrate intake on muscle glycogen storage was investigated. Five well-trained cyclists undertook an exercise trial to deplete muscle glycogen (2 h at 75% of maximal O2 uptake followed by four 30-s sprints) on two occasions, 1 wk apart. For 24 h after each trial, subjects rested and consumed a diet composed exclusively of high-carbohydrate foods, with one trial providing foods with a high GI (HI GI) and the other providing foods with a low GI (LO GI). Total carbohydrate intake over the 24 h was 10 g/kg of body mass, evenly distributed between meals eaten 0, 4, 8, and 21 h postexercise. Blood samples were drawn before exercise, immediately after exercise, immediately before each meal, and 30, 60, and 90 min post-prandially. Muscle biopsies were taken from the vastus lateralis immediately after exercise and after 24 h. When the effects of the immediate postexercise meal were excluded, the totals of the incremental glucose and insulin areas after each meal were greater (P < or = 0.05) for the HI GI meals than for the LO GI meals. The increase in muscle glycogen content after 24 h of recovery was greater (P = 0.02) with the HI GI diet (106 +/- 11.7 mmol/kg wet wt) than with the LO GI diet (71.5 +/- 6.5 mmol/kg). The results suggest that the most rapid increase in muscle glycogen content during the first 24 h of recovery is achieved by consuming foods with a high GI.
