Carrageenan in ulcerative colitis

INTERVENTION: Carrageenan 2‐2.5 g/day vs oat fiber, corresponding dose The study starts with a 7‐day run‐in period (low carrageenan diet, instructed by a dietician), then either a carrageenan period or an oat fiber (control) period for 7 days, followed by at least 14 days' washout (may be slightly longer for some if the 14‐day period is not possible for practical reasons), then after the washout the other treatment (either carrageenan or control). This makes altogether 35 days including one run‐in period, one washout period and two treatment periods. Randomisation: generated by an automated computer service (https://www.sealedenvelope.com/simple‐randomiser/v1/lists ) in blocks of four. CONDITION: Ulcerative colitis ; Digestive System ; Ulcerative colitis PRIMARY OUTCOME: Colitis activity measured using the Simple Clinical Colitis Assessment Index (SCCAI) at baseline and the 7th day of both treatment periods SECONDARY OUTCOME: ; 1. Gastrointestinal symptoms measured by Visual Analog Scale (VAS) 0‐100 at baseline and the 1st, 3rd and 7th day of both treatment periods at the end of the each day; 2. Laboratory tests using blood, urine and stool samples at baseline and at the end (7th day) of both treatment periods:; 2.1. Fecal calprotectin; 2.2. hs‐CRP; 2.3. S‐FABP‐2 (intestinal permeability marker); 2.4. U‐creatinine; 2.5. U‐Albumin; 2.6. F‐albumin; 2.7. F‐IgG; 2.8. F‐intestinal alkaline phosphatase (IAP); 3. Macronutrient and fiber intake measured using a food diary at the end of both treatment periods covering days 5, 6 and 7 (i.e. a 3‐day food diary); INCLUSION CRITERIA: 1. Ulcerative colitis, clinical remission verified by normal fecal calprotectin 2. Aged 18‐64 years 3. No biological medications or systemic cortisone usage for relapse