Method and Study Design: Prospective, open, parallel, group comparison study of 1 intervention group, 1 intervention control group and 1 disease control group. The intervention group and the intervention control group each consist of 30 individuals with IR. Individuals in the intervention group receive an individually adjusted dose of nateglinide 3 times daily during 12 weeks. The third group consists of 10 healthy, young individuals. All groups are followed during 3 months with an otherwise unchanged lifestyle. Endothelial function is measured with the Flow Mediated Dilation method before and after the intervention/observation period.