Impact of the Novel UC-TREAT Diet on the Gut Microbiome and Its Acceptability in Healthy Adults and Adults With Quiescent Ulcerative Colitis

This will be an open-label dietary intervention study recruiting both healthy adults (≥16y) and adults with quiescent Ulcerative Colitis (UC) . The study will span a total of 25 days and is divided into two phases; a 10-day "run-in" observational period and a 15-day dietary intervention period. During the 10-day "run-in" observational period (day -15 to day 0), participants will be asked to continue with their regular habitual diet and record their food intake in a provided estimated weight food diary with food photography for the first 3 of the 10 days. After this "run-in" period, participants will start the 15-day UC-TREAT dietary intervention (day 0 to day 15), where they will consume daily micronutrient supplements, increase intake of berries, and gradually increase intake of dietary fibre and fermented foods. For the first 5 days of the dietary intervention, participants will enter a "ramping" phase, where, with the guidance of the researchers, they will consume 2 portions of berries (blueberries and raspberries) and 1 multivitamin-multimineral tablet each day. Participants will increase their fibre intake by 1 serving of high-fibre food per day until they reach an additional intake of 35g/d and increase fermented food intake by approximately 1 serving per day until they reach at least 5 servings per day. For the final 10 days of the UC-TREAT dietary intervention, participants will enter a "maintenance phase", where they will maintain this additional 35g of fibre intake and at least 5 servings of fermented foods daily. Participants will be asked to record 3 days of food intake in the provided food diaries during this period. The purpose of the ramping period is to reduce the sudden onset of functional abdominal symptoms typically associated with a rapid increase in dietary fibre consumption, including flatulence, bloating, and abdominal cramping. Throughout the study, participants will be asked to provide 3 blood samples (at days -10, 0 and 15), 4 stool and urine samples (at days -10, 0, 10, and 15), and to record a total of 6 days of food intake in provided food diaries. On 4 occasions (days -10, 0, 10, and 15), all participants will be asked to complete a questionnaire assessing their gastrointestinal symptoms (GSRS-IBS), while participants with UC will also be asked to complete a questionnaire assessing their disease-specific quality of life (sIBDQ) and self-reported disease activity (SCCAI). At the end of the study (day 15), all participants will also be asked to complete an acceptability questionnaire to assess their tolerance of the diet.