Morning hyperglycemia plays a role in the future development of insulin resistance and type 2 diabetes (T2D) and is associated with numerous microvascular and cardiovascular complications and renal disease. These augmented morning glucose levels are due to an elevated endogenous glucose production (EGP), as a result of a loss of coordination between glucose levels and insulin secretion, and possibly hyperglucagonemia during the overnight period. Exercise stimulates glucose uptake and increases insulin sensitivity acutely, and may be the best lifestyle intervention to minimize the nocturnal rise in glucose levels. Prescription of the timing of exercise relative to a meal and/or o the overnight period may be particularly critical for individuals that have impaired fasting glucos (IFG) levels. Surprisingly we know little about the overnight period when elevated EGP and the synchrony between glucose and c-peptide/glucagon levels becomes disturbed. This novel study will provide insight into the hormonal/metabolic milieu of a dinner meal, the evening and overnight period that occurs in non-obese, OB and OB+IFG individuals; it will also establish if the timing of exercise can attenuate nocturnal glucose elevations, and if this is associated with improved hormonal synchrony. This project will compare EGP, ?-cell function and hormonal responses between morning and evening exercise on the postprandial and overnight period in obese individuals with/without IFG levels. Fifty-four subjects will be studied during the evening meal (EGP and ?-cell function), postprandially and through the overnight period (1600-0700 h), allowing us to examine some of the potential mechanisms for the elevation in overnight glucose levels. This is the first study that will examine this issue from pre-dinner through the night whil previous studies have only examined chronically fasted individuals and this study will lay the groundwork for understanding the pathology of the predawn phenomena in OB+IFG individuals. These potentially translational findings may impact the efficiency of physician communication to patients concerning exercise. We are one of the few groups that study subjects through the overnight period and have the facilities and capability to do this research.
Many diabetics experience the dawn phenomena or increased glucose levels that cannot be explained by diet alone. This study will identify a causal role for the changes in hormonal synchrony with the increase in glucose levels observed during the overnight period by examining both the dinner meal and exercise as moderators of this effect. Results from this study may allow physicians to more effectively prescribe exercise to patient with impaired fasting glucose levels.