Assessment of Insulin Sensitivity

Participants arrived for the baseline visit after an 8-h fast (hydration with water was allowed). Intravenous access was established and a fasting blood sample was taken for measurement of plasma glucose and serum insulin. An oral load of 75 g glucose was given, and blood was sampled every 30 min over the subsequent 2 h for measurement of plasma glucose and serum insulin. Samples were analyzed by the Clinical Chemistry Laboratory of the University of Minnesota Hospital.

Two indices of insulin resistance were calculated from OGTT data. HOMA-IR is an index of fasting glucose and fasting insulin concentrations. The Matsuda insulin sensitivity index (Matsuda ISI) is calculated from glucose and insulin concentrations fasting and for 2 h following the oral glucose load given during the OGTT. Both indices were calculated as previously described (19,20).