The effect of eight days of strict bed rest on the incretin effect in healthy volunteers

Bed rest and physical inactivity are the consequences of hospital admission for many patients. Physical inactivity induces changes in glucose metabolism, but its effect on the incretin effect, which is reduced in e.g. type 2 diabetes, is unknown. To investigate how eight days of strict bed rest affects the incretin effect, ten healthy non-obese male volunteers underwent eight days of strict bed rest. Before and after the intervention, all volunteers underwent an oral glucose tolerance test (OGTT) followed by an intravenous glucose infusion (IVGI) on the following day to mimic the blood glucose profile from the OGTT. Blood glucose, serum insulin, serum C-peptide, plasma incretin hormones (GLP-1 and GIP), and serum glucagon were measured serially during both the OGTT and the IVGI. The incretin effect, calculated as the relative difference between the area under the curve for the insulin response during the OGTT and that of the corresponding IVGI, respectively. Concentrations of glucose, insulin, C-peptide, and GIP measured during the OGTT were higher after the bed rest intervention (all p<0.05) whereas there was no difference in the levels of GLP-1 and Glucagon. Bed rest led to a mean loss of 2.4 kg of fat-free mass, and induced insulin resistance evaluated by Matsuda Index, but did not affect the incretin effect (p=0.6). In conclusion, eight days of bed rest induces insulin resistance, but we did not see evidence of an associated change in the incretin effect.