Carbohydrate Type And Substrate Utilization

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Does the type of carbohydrate you consume affect substrate utilization during an acute bout of exercise?

Recently researchers from the Sport and Exercise Nutrition Research Group at Loughborough University examined the effects of high and low glycemic index meals on subsequent fuel utilization during exercise. Eight healthy women participated in the investigation and were required to consume either a high or low glycemic index meal three hours prior to completing a one hour run. The one hour run was performed at 60% of the subject' s maximal oxygen consumption capacity. The high glycemic index meal was calculated to have a glycemic index value of 78 while the low glycemic index meal had a value of 44. Both meals were equal in total calories, calories from carbohydrate, protein, and fat. Results of the investigation indicated that the high glycemic meal produced significantly higher insulin levels during the three hour period after meal consumption. During the 60 minutes of exercise the low glycemic index meal resulted in significantly higher plasma levels of both free fatty acids and glycerol when compared to the high glycemic index meal. Additionally, the total amount of fat oxidized after the low glycemic meal was significantly greater than the amount of fat utilized after the high glycemic index diet. Based upon this research it might be concluded that a low glycemic diet will facilitate the oxidation of fats during exercise, thus potentially having a greater impact on body fat loss. The authors suggested that further research is needed to determine if the same affect occurs in response to low glycemic index diets when variable exercise intensities are used.

Stevenson EJ, Williams C, Mash LE, Phillips B, Nute ML. (2006). Influence of high-carbohydrate mixed meals with different glycemic indexes on substrate utilization during subsequent exercise in women. American Journal of Clinical Nutrition, 84(2):354 — 360.