Protease Regulation and Impact of Sodium as Mechanisms of Inflammation in IBD

This longitudinal exploratory study has two related phases: Phase 1 will enroll 300 Crohn's disease (CD) patients from McMaster's IBD and IBD Nutrition Clinics to assess dietary sodium intake and fecal proteolytic activity in relation to disease activity (active/inactive). Participants will be followed annually for 2 years, forming a registry. At baseline and each follow-up visit, data collected will include: demographics, BMI, CDAI, diet (1-week food recall via Keenoa and 6-month sodium questionnaire), blood (sodium, metabolomics, CRP), stool (microbiota, metabolomics, fecal calprotectin, proteolytic activity), and spot urine (sodium, potassium, creatinine, metabolomics). Extra visits will occur if a disease flare happens. Phase 2 will involve 80 participants from Phase 1 (40 high-sodium diet \[HSD\], 40 low-sodium diet \[LSD\]), selected based on sodium intake. Over three visits (baseline, week 1, week 2), participants will provide fecal samples for microbiota and metabolomics analysis, and blood/urine samples (baseline and week 2). Colonoscopy with biopsies and video will be performed at week 2. Diet will be closely tracked using Keenoa to assess intake of sodium, carbs, UPF, fibre, and calories. After Phase 2, participants return to Phase 1 follow-up.