Statistical e sample size: A sample of 16 individuals has been estimated to be sufficient to demonstrate a difference of 10 mg/dl in the basal glucose concentration with 90% power and a significance level of 95% and a drop-out rate of 10% at the 8th weeks of treatment. A sample of 34 individuals in each group has been estimated to be sufficient to demonstrate a difference of 1,4 point in the HOMA-IR index with 90% power and a significance level of 95% and a drop-out rate of 10% at the 8th weeks of treatment. Statistical significance will be assumed at P< 0.05. The statistical analysis will be performed with SPSS for Windows version 17.0 (SPSS Inc., Chicago, IL, USA).