Mucosal analysis: Duodenal biopsies (14 pinch biopsies, consistent with previous trials) will be taken by a nationally and trial accredited gastroenterologist supported by a sedationist in an accredited facility. Four biopsies will be committed for conventional histology. To ensure standardisation the Biopsy forceps to be used will be Boston Scientific Radial Jaw® 4 - 2.8mm. Paraffin embedded tissue sections (3 μm) will be stained with H&E and anti-cluster of differentiation 3 (anti-CD3). Clinical histopathology will be supervised by a specialist in gastrointestinal pathology (A/Prof. Andrew Clouston) and reported contemporaneously for clinical purposes. Best representative field images from each case will be selected by Prof. Clouston, then coded in re-identifiable format before adding to an access-restricted and secure database, and later scored for intraepithelial lymphocytes (IEL)% and V:C by a single pathologist (Dr. Greg Miller). At each time point, two four biopsy tissue samples will be stored at -80°C in 10% glycerolRNA stabilisation solution for future gene expression and microbiota analyses.