 Power calculation: Fresh faecal and urine samples will be collected from 38 healthy participants at 4 time points. Based on our previous in vivo work in children with CD this would give us a power of 80 p0.05 to detect a mean concentration difference of 1.0 log SD:1.5 in Faecalibacterium prausnitzii between their habitual diet and EEN diet or the CD-TREAT diet. 