The primary purpose of this study is to determine the effectiveness of a low-fat or standard American diet (high in fat) in helping people with ulcerative colitis improve their symptoms and the signs of inflammation in blood tests and in bowel biopsies.

Inclusion Criteria:

1. Male or Female ≥18 and ≤70 years old

2. History of UC of at least 3 months duration

3. UC should be confirmed by colonoscopy within two years of entry into the study

4. Patients with mild to moderate UC, or patients in remission that have had active disease within the past 18 months, regardless of treatment with mesalamines, immunosuppressants, anti-TNFs and/or vedolizumab

   • Patients on oral 5-aminosalicylates, mesalamine or sulfasalazine must be on a stable dose for ≥2 weeks prior to screening
   • Patients treated with anti-TNFs or immunosuppressants (AZA, 6-MP, or methotrexate) at screening must have been on a stable dose for ≥8 weeks and remain on the same dose during the treatment period
   • Patients on steroids can be on no more than prednisone 20mg daily or budesonide 9mg daily at screening. If clinically indicated, tapering of steroids after 4 weeks of intervention may occur. Prednisone may be tapered by no more than 2.5mg/week and budesonide by no more than 3mg/week.
   • Patients on infliximab, premedication may include intravenous corticosteroid

5. No antibiotic use or probiotic use within 4 weeks prior to screening

6. Signed written informed consent for enrollment into the study

Exclusion Criteria:

1. Patients with Crohn's Disease and Celiac Disease

2. History of colonic dysplasia except for adenoma on prior surveillance colonoscopy

3. Patients with altered anatomy: prior colectomy or anticipated colectomy during the study period and presence of ileal pouch or ostomy

4. Clinical manifestations concerning for fulminant disease or toxic megacolon

5. Patients with stool sample positive at during screening period or at least <12 weeks for ova, parasites, or culture for aerobic pathogens including: Aeromonas, Plesiomonas, Shigella, Yersinia, Campylobacter and E.coli spp. or positive for Clostridium difficile B toxin in stools

6. Use of cyclosporine, mycophenolate mofetil, sirolimus, thalidomide or tacrolimus within 2 months prior to screening

7. Need for prednisone >20mg daily or budesonide >9mg daily at the time of screening

8. Received intravenous corticosteroids within 2 weeks prior to screening, during screening, or during the study period, except as premedication for anti-TNFs

9. Use of Total Parenteral Nutrition at the time of screening and during the study period

10. Anti-diarrheal use within 2 weeks prior to screening

11. Presence of any of the following laboratory abnormalities during screening period or at least <12 weeks

    • Hemoglobin <8.0g/dl
    • Albumin <2.8g/dl

12. Conditions/situations such as:

    • Patients with short life expectancy
    • Uncooperative behavior or any condition that could make the patient potentially non-compliant to the study procedures
    • Patients with pacemaker
    • Other significant or life-threatening co-morbidities in which diet intervention could negatively affect

13. Failure to meet any of the inclusion criteria

14. Poor compliance with diet during the study period

15. Failure to submit stool samples as indicated at each phase of the study

16. The need for antibiotic use during the study period