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Effect of Acute Prior Exercise on Glycemic and Insulinemic Indices

Department of Food Science and Human Nutrition (V.E., K.W., W.L., M.S.H., C.L.M.), Colorado State University, Fort Collins, Colorado
Department of Health and Exercise Science (M.S.H.), Colorado State University, Fort Collins, Colorado

Address correspondence to: Christopher L. Melby, Dr.P.H., Professor and Head, Department of Food Science and Human Nutrition, Nutrition and Metabolic Fitness Laboratory, 216 Gifford, Colorado State University Fort Collins, CO 80523. E-mail: Christopher.melby{at}colostate.edu

Background: Acute exercise is associated with increased insulin sensitivity characterized by increased insulin-induced glucose transport for periods of up to 48h after the bout of exercise. This suggests that the glycemic response to a meal may be altered by prior exercise.

Objective: We tested the hypothesis that the glycemic and insulinemic responses to a test food consumed following exercise would be lower than when consumed without prior exercise.

Design: Four lean males (age: 27 ± 4 y) and 4 females (age: 23 ± 3 y) completed 3 experimental conditions in random order: ExCHO—Subjects exercised on a cycle ergometer at 70% VO_2peak with a net energy cost of 400 kcal, which was followed by consumption of a high carbohydrate (CHO) energy bar; NoExCHO—Same as ExCHO except subjects sat quietly rather than exercised; and NoExGlc—Same as NoExCHO except subjects consumed a 50 g glucose (glc) drink as the reference CHO for GI and insulinemic index (II) determination. For each condition, following exercise or rest, baseline venous blood samples were obtained. Postprandial blood samples were obtained at 15 min intervals for 2 h.

Results: Neither the 2-h glucose area under the curve (AUC) or the GI were different between ExCHO and NoExCHO. The insulin AUC for ExCHO was 28% lower than the insulin AUC for NoExCHO (p = 0.03). The calculated II for the ExCHO condition was 30% lower than that of NoExCHO (p = 0.05).

Conclusions: An acute bout of prior exercise had no effect on the GI of an energy bar compared to that of the same food determined under the standard no-exercise conditions. However, prior exercise resulted in a lower 2-h insulin response to the CHO-rich energy bar.

Key words: exercise, carbohydrate, glycemic index, insulin, humans