Imperial College London - Department of Paediatrics, Imperial College London, Busitema University - Mbale Clinical Research Institute, Busitema University - Mbale Clinical Research Institute, Busitema University - Mbale Clinical Research Institute, Kenya Medical Research Institute (KEMRI)– Wellcome Trust Research Programme, University of Reading - Department of Food and Nutritional Sciences, University of Glasgow, University of Glasgow - Stable Isotope Biochemistry Laboratory, Imperial College London, Imperial College London - Department of Metabolism, Digestion and Reproduction and Imperial College London - Department of Paediatrics