Background: Serum insulin and leptin levels correlate positively. It is not known whether this relation remains the same in cases of severely disturbed insulin secretion and after rapid weight loss. We therefore studied the relation between insulin and leptin in obese type 2 diabetic patients before and after considerable weight loss.
Methods: In 17 obese type 2 diabetic patients, blood glucose-lowering medication was discontinued (day-1) and a 30-day very low calorie diet (VLCD, 450 kcal/day) was started. On days 0, 2, and 30, body weight, body fat mass [with bioelectrical impedance analysis (BIA)], fasting serum glucose, insulin, and leptin were determined. Homeostatic model assessment was used to estimate insulin resistance (HOMA-IR) and beta-cell function (HOMA-beta). On days 2 and 30, an intravenous glucose tolerance test (IVGTT) was performed.
Results: Fasting serum leptin levels correlated positively with fasting serum insulin levels (r=0.72, p=0.001 on day 2; r=0.78, p=0.001 on day 30) and area under the curve (AUC) of insulin (r=0.74, p=0.001 on day 2; r=0.84, p=0.0001 on day 30), as well as HOMA-beta, as a measure of insulin secretion, even after correction for body mass index (BMI) and body fat mass, with which leptin was also positively correlated.
Conclusion: In a group of obese type 2 diabetic patients with a wide range of residual endogenous insulin secretion, we found a positive relation between fasting serum leptin and insulin levels, even after correction for BMI and body fat mass. This was true both before weight loss and during energy restriction with weight loss.