Background & objective: Indians have decreased insulin sensitivity (IS) and a greater adiposity at a lower body mass index (BMI) when compared with other ethnic groups. Despite this, IS has not been studied in Indians of low BMI. This study thus used the hyperinsulinaemic euglycaemic clamp (HEC) technique to compare IS in young normal weight (NW) and low BMI (LBMI) Indian males. Clamp IS was also compared with convenient indices of insulin sensitivity such as the homeostatic model assessment (HOMA). In the NW group, clamp IS was compared with published data of similarly measured IS in other studies and ethnic groups.
Methods: Ten NW [body mass index (BMI): 18.5-25 kg/m(2)] and ten LBMI (BMI < 18.5 kg/m(2)) young healthy Indian males aged between 19-32 yr were recruited through advertisements from Bangalore slums. Fasting plasma glucose and insulin, glucose disposal rates (GDR) and IS were the parameters measured during the HEC technique.
Results: The NW group had a Clamp IS of 4.5 (3.8, 5.3) (median, lower, upper quartile, mg/(kg x min)/microU/ml) that was close to half that of the LBMI group; 9.9 (7.1, 13.4: P<0.001). Clamp IS in the NW group was significantly lower than that observed in published studies involving other ethnic groups (P<0.05). Clamp IS and per cent body fat (% BF), were significantly and negatively correlated (n = 20, rho = -0.7, P<0.001). Correlations between Clamp IS and other IS indices ranged from rho = -0.5 for HOMA2-%B to rho = 0.5 for HOMA2-%S (P<0.05); however, the correlation with HOMA1-IR was not significant (rho = 0.4).
Interpretation & conclusion: The significantly lower Clamp IS of the NW group compared with the LBMI group and other ethnic groups indicated that IS was impaired in Indians at relatively low BMIs. Most of the convenient indices of IS were significantly correlated with Clamp IS, however, the Clamp IS was more sensitive method with greater discriminatory power, since IS differences between LBMI and NW groups were only apparent with Clamp IS.