Effect of body composition on indices of insulin sensitivity and beta-cell function in healthy men

Several indices have been published to quantify insulin sensitivity from fasting plasma glucose and fasting plasma insulin levels as well as from the data obtained by the oral glucose tolerance test (oGTT). Obesity represents the main risk factor associated with development of insulin resistance and Type 2 diabetes mellitus. The aim of this study was to evaluate the influence of body composition on various indices of insulin sensitivity and secretion in subjects with normal glucose tolerance.

A total of 33 male subjects (aged 26-51 years, BMI 19.7-30.9 kg/m2) underwent a standard oral glucose tolerance test (oGTT). Thereafter the cut-off value of BMI = 25 kg/m2 was set to divide the group into normal subjects and subjects with overweight. Indices of insulin sensitivity and secretion were calculated from plasma glucose and insulin concentrations using the formulas proposed by Matthews et al. (1985), Cederholm and Wibell (1990), Matsuda and DeFronzo (1999) and Stumvoll et al. (2000).

All subjects had a normal glucose tolerance according to standard diagnostic criteria. No difference was found in the course of glycemia, while overweight subjects displayed an enhanced insulin response (P < 0.01). BMI correlated closely with all indices. The correlation coefficient was highest in ISI(Matsuda), followed by ISI(Cederholm) and ISI(Stumvoll). The indices of insulin sensitivity all significantly increased in the overweight group. The groups did not differ in the values of index SecrHOMA.

The easiest way to predict the insulin sensitivity and to control the development of insulin resistance in a subject with yet normal glucose tolerance, but at high risk of development of overt Type 2 diabetes is to calculate an index from glucose and insulin concentrations during an oGTT. However, the assessment of appropriate cut-off values is necessary for introducing the indices in clinical practice.