by Dr. Paul Cribb Ph.D. CSCS.
AST Director of Research
Researchers from Loughborough University examined the effects of high and low glycemic index meals (GI) 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 run was performed at 60% of the subject’s maximal oxygen consumption capacity. The high glycemic index (GI) meal (a value of 78) and low GI meal (a value of 44) were both equal in total calories, carbohydrate, protein, and fat.
Results of the investigation indicated that the high GI meal produced higher insulin levels during the three hours after meal consumption. During the exercise, the low GI meal resulted in higher blood levels of both free fatty acids and glycerol, indicating a greater utilization of fat for fuel. Additionally, the total amount of fat oxidized after the low GI meal was significantly greater than the amount of fat utilized after the high GI meal.
Based on this research it might seem as though a low GI diet will facilitate the burning of fats during exercise, thus potentially having a greater impact on body fat loss.
However, it’s important to remember that the exercise protocol involved very moderate-intensity exercise. The effects of high-intensity exercise need to be examined. Also, the amount of fat (calories) burnt during exercise is relatively small (only 3%) when compared to overall daily calorie expenditure. Scientists need to look at the amount of calories (fat) burnt over the course of the entire day or week.
What this research does provide is important insights into the effects of consuming low GI meals during the hours outside of exercise. Low GI meals during the day will promote greater utilization of fat for fuel. As part of a calorie-controlled eating plan, this will promote effective fat loss over the long term.
Source: American Journal of Clinical Nutrition, 84;354-360, 2006.
