In the 21st century, the incidence of inflammatory bowel disease (IBD) globally increases. Higher incidence of IBD development may implicate that environmental factors played essential roles in IBD pathogenesis. One of the environmental factors is a westernized diet that contains a high amount of animal protein and a low amount of dietary fiber. This kind of diet can lead to gut microbial dysbiosis and increase susceptibility to IBD. A microbial dysbiosis pattern in IBD is a decrease in microbial diversity and the inversed ratio of local protective and pathologic bacteria. High animal protein was associated with an increased risk of IBD and increased risk of disease relapse meanwhile dietary fiber was associated with IBD risk reduction. A semi-vegetarian diet is a diet with high fiber and low red meat and processed food that may reduce inflammatory activity in IBD. The study in the semi-vegetarian diet in IBD activity is still limited.

This study aimed to evaluate a semi-vegetarian diet's effect in maintaining IBD remission in disease quiescence patients.

This study is a prospective interventional cohort in clinically quiescence IBD patients in Siriraj Hospital, Mahidol University, Bangkok, Thailand. At enrollment, clinical information, dietary intake, inflammatory markers, and fecal microbiota will be recorded. Dietary intake will be assessed by an experienced nutritionist using pictures of food, a dietary questionnaire, and patient interviewing. The nutritionist advises the participants to consume a semi-vegetarian diet which includes high dietary fiber consumption and low red meat and processed food consumption. All patients will be required to send all pictures of food intake three days in 1 week before every visit, including two weekdays and one weekend. The dietary component will be analyzed using Nutrient calculation computer software INMUCAL-Nutrient V3 database NB1 (Institute of Nutrition, Mahidol University. Nakornpathom. 2013). The study will take 1 year including 6 visits (including baseline, 6th weeks, 18th week, 30th week, 42nd week, 54th week) for each patient. The primary outcome is the effect of increasing fiber diets and decreasing red meat and processed food on maintaining clinical remission in IBD. Secondary outcomes are the effect of modifying diet on change of inflammatory markers, microbiota, and quality of life.

Inclusion Criteria:

1. Patients with Crohn's disease or Ulcerative colitis
2. Age ≥ 18 years old
3. Disease in remission at least 2weeks by following criteria Crohn's disease: Crohn's Disease Activity Index(CDAI) < 150 Ulcerative colitis: Mayo Ulcerative Colitis Subscore ≤ 2
4. Prednisolone ≤ 15 mg/day for at least 1 month
5. Stable immunomodulator dosage at least 1 month
6. Stable biologic agent at least 2 months

Exclusion Criteria:

1. Patients with Ulcerative colitis with a history of proctocolectomy
2. Patients with Crohn's disease with bowel stricture
3. Patients with recently antibiotic usage within 1 month
4. Pregnant patients