Endogenous insulin secretion ability in meal tolerance test correlated with body mass index (BMI) in Japanese type 2 diabetes patients

Several studies report that endogenous insulin secretion (EIS) ability is correlated with BMI in glucagon stimulation tests (GST). Despite a standard method to assess EIS, GST can produce side effects such as nausea. Therefore, we investigated the relationship between EIS and BMI with a simple meal tolerance test (MTT). One-hundred type 2 diabetes mellitus (T2DM) patients (average: age 61, HbA1c 9.2 %, BMI 25.0 kg/m², duration of DM 11.5 years) subjected to a MTT. We measured serum C-peptide immunoreactivity (CPR) at fasting, and 2 h after a calorie controlled breakfast, and calculated the difference to give ΔCPR. The fasting and postprandial CPR significantly correlated with BMI (R = 0.59, R = 0.48, P < 0.0001, respectively). ΔCPR also significantly correlated to BMI (R = 0.34, P < 0.001). HbA1c had a significant negative association of ΔCPR (R = −0.38, P < 0.0005). The optimal cut-off level of BMI to predict ΔCPR <1.0 was 20.5 kg/m² using the ROC curve (sensitivity 83 %, specificity 88 %). Using multiple regression analysis, we examined influence factors of ΔCPR; the significant standard partial regression coefficients were: BMI 0.254, insulin use −0.237, HbA1c -0.358 (P < 0.05). The HbA1c level in BMI > 25.0 kg/m² was significantly higher in patients with 1.0 < ΔCPR <2.0 than patients with ΔCPR > = 2.0 (10.0 % vs. 8.5 %). The BMI significantly correlated with EIS ability in a MTT, and is a simple index to predict EIS. The insulin secretion ability diminished in patients with BMI <20 kg/m², and BMI > 25 kg/m² but high HbA1c > 10 %.