HOMA IR = (fasting glucose [mmole] /lt X fasting insulin [μU/ml])/22.5). The insulinogenic index, a commonly used indicator of pancreatic β-cell function, was calculated as the ratio of increment of insulin concentrations to that of glucose concentrations at 30 minutes after meal ingestion (Δ [ins30 - ins0] / Δ [Glu30 -Glu0]).