1. Biostatistics Research Unit, South African Food Data System (SAFOODS) Division, South African Medical Research Council, Francie van Zijl Drive, Parow Valley, Tygerberg 7505, Cape Town P.O. Box 19070, South Africa
2. Department of Consumer and Food Sciences, University of Pretoria, Private Bag X20, Hatfield 0028, South Africa
3. Department of Global Health, Division of Human Nutrition, Faculty of Medicine and Health Sciences, Stellenbosch University, Francie van Zijl Drive, Tygerberg 7505, Cape Town P.O. Box 19063, South Africa