Although chest infections affect wellbeing and survival in cystic fibrosis (CF), most people with CF also have difficulty digesting food and must take medication for this. In spite of this treatment, two thirds of people with CF miss school or work because of tummy symptoms (pain, bloating and wind). In some cases these symptoms become severe leading to bowel obstruction and hospital admission. Long term, people with CF have a greater risk of bowel cancer. The investigators asked people with CF and health professionals to suggest the most important questions for research. Treatment of gut symptoms was in their top 10 list. Current treatments are often ineffective because the investigators do not fully understand why symptoms occur. GRAMPUS-CF SRC will describe accurately the categories of gut symptoms in CF and find out why they occur. The investigators will do this using magnetic resonance imaging (MRI) scans and tests which give a detailed description of the germs in the bowel or which measure inflammation. The investigators will also study the effects of diet, using a questionnaire. The investigators will link these results together, using advanced statistics to find the factors causing gut symptoms. The investigators will then identify treatments which are likely to be helpful. In future work the investigators will test these in clinical trials.