Plasma insulin concentration is more tightly linked to plasma leptin concentration than is the body mass index.

This study tested the hypothesis that the integrated plasma insulin response to oral glucose is a more sensitive predictor of the fasting plasma leptin concentration than the body mass index (BMI) or waist to hip ratio (WHR). For this purpose, we determined the fasting plasma leptin concentration and plasma insulin response to a 75-g oral glucose challenge in 76 healthy female subjects, with a BMI of 19.1 to 36.6 kg/m2 and a WHR of 0.57 to 1.1. The results demonstrated that fasting plasma leptin concentrations were significantly correlated with both the BMI (r = .64, P < .001) and the plasma insulin response to glucose (r = .61, P < .001), but not with the WHR (r = .27). Since the BMI and the insulin response were also significantly related (r = .34, P = .003), multivariate analysis was performed to determine if the BMI and insulin response were independent determinants of the fasting leptin concentration. This analysis indicated that both the BMI and insulin response were significantly related to plasma leptin (P < .001). To pursue this issue further, the population was divided into tertiles on the basis of the (1) plasma leptin concentration, (2) BMI, and (3) integrated insulin response. The two variables that were most closely linked to each other were the leptin concentration and insulin response. In contrast, the BMI was relatively easily disassociated from the other two variables. These results indicate that while both the plasma insulin response to glucose and the BMI are significantly associated with the fasting plasma leptin concentration, the plasma insulin response appears more closely associated with the plasma leptin concentration.