Response to treatment will be assessed according to clinical review, CD activity score and measurements of established biomarkers in faeces and blood (e.g. faecal calprotectin). The primary endpoint will be clinical response (Adults: HBI fall≥3; Children: wPCDAI fall≥17.5) or clinical remission (Adults: HBI<5; Children: wPCDAI<12.5) at 8 weeks; while secondary endpoints include reduction in faecal calprotectin and blood inflammatory markers and changes in anthropometry. All patients will be under close follow-up. No new CD-related medications will be allowed during the pilot study, however if patients' disease activity is deteriorating at any point during the study or there is no response at 4 weeks, patients will be eligible to discontinue CD-TREAT diet and commence medical/surgical treatment as deemed necessary by the treating clinical team. Those participants will still be encouraged to provide stool, blood and urine samples at intervention exit. For those demonstrating response, all background CD-related medication dosages will remain stable unless a subject develops specific drug-related side-effects, blood monitoring abnormalities or blood drug levels requiring alteration. Those patients who experience clinical response but not clinical remission at 8 weeks will be given the opportunity to stay on CD-TREAT for a further 4 weeks. At the end of this period (12 weeks post CD-TREAT initiation) they will be asked to provide the last stool and urine sample and they will have the last follow-up appointment including collection of research bloods, clinical review, quality of life assessment and anthropometry measurements.