Effect of training on response to a glucose load adjusted for daily carbohydrate intake

Functional adaptation of the human β-cells after frequent exposure to noradrenaline

Physical training decreases glucose- and arginine-stimulated insulin secretion. The mechanism by which the pancreatic β-cells adapt to the training status of the individual is not known. We hypothesized that the adaptation is mediated via the frequent exercise-induced increases in sympathetic activity. Simulation of exercise-induced increases in plasma noradrenaline (NA) concentrations was carried out in nine untrained men (age: 25 ± 1 years (mean ± SEM); BMI: 24 ± 1 kg m(-2) ), who received infusions of NA (0.2 μg kg(-1) min(-1) ) for 45 min every day for 10 days. The insulin response to glucose was measured during hyperglycaemic (20 mmol l(-1) ) clamps before and after the NA infusion period. During NA infusions mean arterial blood pressure increased (from 89 ± 2 to 110 ± 5 mmHg, P < 0.05) and heart rate decreased (from 78 ± 7 to 69 ± 12 beats min(-1) , P < 0.05). During NA infusions plasma insulin concentrations decreased to nadir by 68% (P < 0.05). Fasting plasma glucose and insulin were not different at the two clamps (5.3 ± 0.1 and 5.3 ± 0.3 mmol l(-1) ; 47 ± 15 and 31 ± 4 pmol l(-1) , respectively). Plasma glucose concentrations during the hyperglycaemic clamps were similar (P > 0.05) and averaged 19.9 ± 0.1 mmol l(-1) with a coefficient of variation of 3.8 ± 0.3%, while the insulin response decreased (P < 0.05) by 26 ± 2% after the 10 days of NA infusions. It is concluded that NA mediates the adaptation of the β-cells seen in trained people.

Meal induced gut hormone secretion is altered in aerobically trained compared to sedentary young healthy males

Postprandial insulin release is lower in healthy aerobically trained (T) compared to untrained (UT) individuals. This may be mediated by a lower release of the two incretin hormones [glucagon like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP)] in T. The aim of this study was to assess and compare gut hormone response and satiety changes after a liquid meal intake in young, healthy T and UT males. Postprandial gut hormone release and subjective feelings of hunger, satiety, fullness and prospective food consumption were assessed before and frequently for the following 3 h after a 200 ml liquid meal (1,260 kJ and 27, 41 and 32 energy % as protein, carbohydrates and fat, respectively) in ten T and ten UT young, healthy male subjects. The insulin and GIP responses were markedly lower in T than UT and correlated during the first 30 min after the liquid meal. Baseline GLP-1 concentration was higher in T versus UT, but the response in the following 3 h after a liquid meal was similar in T and UT. Satiety measures did not differ between groups throughout the test. It is possible that in aerobically T subjects, a lower GIP release is partly responsible for a lower postprandial incretin stimulated insulin secretion.

Influence of acute exercise with and without carbohydrate replacement on postprandial lipid metabolism

Acute exercise, undertaken on the day before an oral fat tolerance test (OFTT), typically reduces postprandial triglycerides (TG) and increases high-density lipoprotein-cholesterol (HDL-C). However, the benefits of acute exercise may be overstated when studies do not account for compensatory changes in dietary intake. The objective of this study was to determine the influence of acute exercise, with and without carbohydrate (CHO) replacement, on postprandial lipid metabolism. Eight recreationally active young men underwent an OFTT on the morning after three experimental conditions: no exercise [control (Con)], prolonged exercise without CHO replacement (Ex-Def) and prolonged exercise with CHO replacement to restore CHO and energy balance (Ex-Bal). The exercise session in Ex-Def and Ex-Bal consisted of 90 min cycle ergometry at 70% peak oxygen uptake (V̇o2peak) followed by 10 maximal 1-min sprints. CHO replacement was achieved using glucose solutions consumed at 0, 2, and 4 h postexercise. Muscle glycogen was 40 ± 4% ( P < 0.05) and 94 ± 3% ( P = 0.24) of Con values on the morning of the Ex-Def and Ex-Bal OFTT, respectively. Postprandial TG were 40 ± 14% lower and postprandial HDL-C, free fatty acids, and 3-hydroxybutyrate were higher in Ex-Def compared with Con ( P < 0.05). Most importantly, these exercise effects were not evident in Ex-Bal. Postprandial insulin and glucose and the homeostatic model assessment of insulin resistance (HOMAIR) were not significantly different across trials. There was no relation between the changes in postprandial TG and muscle glycogen across trials. In conclusion, the influence of acute exhaustive exercise on postprandial lipid metabolism is largely dependent on the associated CHO and energy deficit.