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Original Research Communication |
1 From the Human Performance Laboratory, Department of Kinesiology and Health Education, The University of Texas at Austin (SS, CJD, TWZ, and EFC), and the Stable Isotope Laboratory, Pennington Biomedical Research Center, Baton Rouge, LA (LOB).
Correspondence: 3 Address reprint requests to EF Coyle, Department of Kinesiology and Health Education, The University of Texas at Austin, Bellmont Hall 222, Austin, TX 78712. E-mail: coyle{at}mail.utexas.edu.
Background: The glycemic index (GI) of a food is thought to directly reflect the rate of digestion and entry of glucose into the systemic circulation. The blood glucose concentration, however, represents a balance of both the entry and the removal of glucose into and from the blood, respectively. Such direct quantification of the postprandial glucose curve with respect to interpreting the GI is lacking in the literature.
Objective: We compared the plasma glucose kinetics of low- and high-GI breakfast cereals.
Design: On 2 occasions, plasma insulin concentrations and plasma glucose kinetics (by constant-rate infusion of [6,6-2H2]glucose) were measured in 6 healthy males for 180 min after they fasted overnight and then consumed an amount of corn flakes (CF) or bran cereal (BC) containing 50 g available carbohydrate.
Results: The GI of CF was more than twice that of BC (131.5 ± 33.0 compared with 54.5 ± 7.2; P < 0.05), despite no significant differences in the rate of appearance of glucose into the plasma during the 180-min period. Postprandial hyperinsulinemia occurred earlier with BC than with CF, resulting in a 76% higher plasma insulin concentration at 20 min (20.4 ± 4.5 compared with 11.6 ± 2.1 µU/mL; P < 0.05). This was associated with a 31% higher rate of disappearance of glucose with BC than with CF during the 30–60-min period (28.7 ± 3.1 compared with 21.9 ± 3.1 µmol · kg-1 · min-1; P < 0.05).
Conclusion: The lower GI of BC than of CF was not due to a lower rate of appearance of glucose but instead to an earlier postprandial hyperinsulinemia and an earlier increase in the rate of disappearance of glucose, which attenuated the increase in the plasma glucose concentration.
Key Words: Carbohydrate • glucose kinetics • protein • nutrition • hyperinsulinemia
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