1. Obesity and Diabetes Clinical Research Section, Phoenix Epidemiology and Clinical Research Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Phoenix, Arizona.
2. Division of Endocrinology, Department of Medicine, Phoenix VA Health Care System, Phoenix, Arizona.
3. Clinical Core Laboratory, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland.
4. Obesity Research Center, Endocrinology Unit, University Hospital of Pisa, Pisa, Italy.