1. Business Unit Analytical Sciences and Business Unit Physiological Sciences, TNO Quality of Life, P.O. Box 360, 3700 AJ Zeist, The Netherlands, BioAnalytical Science Department, Nestlé Research Center, P.O. Box 44, CH-1000 Lausanne 26, Switzerland, and School of Biomedical Sciences, University of Nottingham Medical School, Queen's Medical Centre, Clifton Boulevard, Nottingham, NG7 2UH, United Kingdom