Department of Internal Medicine IV, Division of Diabetology, Endocrinology and Nephrology, University Hospital Tübingen, Otfried-Müller-Str. 10, 72076, Tübingen, Germany. Institute for Diabetes Research and Metabolic Diseases of the Helmholtz Center Munich at the University of Tübingen, Tübingen, Germany. German Center for Diabetes Research (DZD e.V.), Neuherberg, Germany. Institute for Clinical Chemistry and Pathobiochemistry, Department for Diagnostic Laboratory Medicine, University Hospital Tübingen, Tübingen, Germany. Modern Diet and Physiology Research Center, Department of Psychiatry, Yale University, New Haven, CT, USA. Department of Internal Medicine IV, Division of Diabetology, Endocrinology and Nephrology, University Hospital Tübingen, Otfried-Müller-Str. 10, 72076, Tübingen, Germany. martin.heni@med.uni-tuebingen.de. Institute for Diabetes Research and Metabolic Diseases of the Helmholtz Center Munich at the University of Tübingen, Tübingen, Germany. martin.heni@med.uni-tuebingen.de. German Center for Diabetes Research (DZD e.V.), Neuherberg, Germany. martin.heni@med.uni-tuebingen.de. Institute for Clinical Chemistry and Pathobiochemistry, Department for Diagnostic Laboratory Medicine, University Hospital Tübingen, Tübingen, Germany. martin.heni@med.uni-tuebingen.de.