Introduction: After food ingestion, the incretin hormones, glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP), are secreted by the intestines into circulation where they act on the pancreas to promote insulin secretion. We evaluated the hypothesis that low postprandial plasma insulin levels in lean exercise-trained individuals are associated with low concentrations of incretin hormones.
Methods: A cross-sectional study was performed to compare postprandial incretin hormone levels in lean endurance exercise-trained individuals (EX; n = 14, ≥40 yr) and age- and sex-matched, nonobese, sedentary control subjects (CON, n = 14). The main outcome measures were GLP-1, GIP, insulin, and glucose incremental areas under the curve (AUC) as measured in plasma samples collected during a 2-h,75-g oral glucose tolerance test (OGTT).
Results: The EX group had lower body fat percentage (14.6% ± 1.1% vs 23.3% ± 1.7%, P = 0.0002) and higher maximal oxygen uptake (53 ± 2 vs 34 ± 2, P < 0.0001) than CON. Glucose AUC did not differ between groups (P = 0.20). Insulin AUC was lower in EX (2.5 ± 0.5 vs 4.2 ± 1.2 μU·mL−1·1000 min−1, P = 0.02). No differences were observed between groups (EX and CON, respectively) for GLP-1 AUC (3.5 ± 0.7 vs 4.1 ± 1.1 pmol·min−1·100 L−1, P = 0.61) or GIP AUC (19.2 ± 1.4 vs 18.0 ± 1.4 pg·min−1·1000 mL−1; P = 0.56). In CON, insulin AUC was correlated with AUC for GLP-1 (r = 0.53, P = 0.05) and GIP (r = 0.71, P = 0.004), but no such correlations were observed in EX (both P ≥ 0.67).
Conclusions: Low postprandial insulin levels in lean exercise-trained individuals are not attributable to lower incretin hormone concentrations. However, exercise may decrease the dependency of postprandial insulin levels on incretin hormones.
1Department of Nutrition and Dietetics, Saint Louis University, St. Louis, MO; 2Division of Geriatrics and Nutritional Science, Department of Medicine, Washington University School of Medicine, St. Louis, MO; 3Department of Biology, Saint Louis University, St. Louis, MO; 4Department of Medicine, Salerno University Medical School, Salerno, ITALY; and 5CEINGE Biotecnologie Avanzate, Napoli, ITALY
Address for correspondence: Edward P. Weiss, Ph.D., Department of Nutrition and Dietetics, Saint Louis University, 3437 Caroline Street, St. Louis, MO 63104; E-mail: firstname.lastname@example.org.
Submitted for publication May 2013.
Accepted for publication October 2013.