Following ethical consent the participants who are due to commence CSII will be observed at 5 time points (every three months) over a year. It should be noted that the recruitment period for the longitudinal arm of the study will be 9 months starting from the date the first participant is recruited. At each time point each participant will be asked to complete a 5 day food diary, a food intake questionnaire (FIQ), a quality of life (QOL) questionnaire, a semi-structured interview and give a 20ml sample of blood. This will be taken at the same time and in addition to their regular diagnostic sample, however where this is unfeasible extra occasional appointments may be needed. Results will be compared with existing patient medical records, which will also be analysed during the study.