Inclusion Criteria:
* Known diagnosis of ulcerative colitis.
* Evidence of active disease, defined as either 1) measured FCP \>100 µg/g at screening, OR 2) Partial Mayo Scoring Index Assessment for UC ≥2 (adult patients) OR Pediatric UC Activity Index (PUCAI) ≥10 (pediatric patients). Patients who are in clinical remission (Partial Mayo \<2 or PUCAI \<10) that have active inflammation (elevated FCP \>100 µg/g) would also be eligible, as will patients with active symptoms, regardless of availability of FCP.
* Tanner stage ≥4 for pediatric patients.
* Weight \>40kg.
* No changes to IBD-related medications in three months prior to study onset (stable therapy, including use of 5-aminosalicylic acid, biologics, and immunosuppressive medications; some minor adjustments allowed, such as increasing dose for weight change, or change to a compatible/generic treatment).
* Men and women that use adequate contraceptive methods.
* Able to maintain current lifestyle (diet, exercise, supplements/medications, and sleep) throughout study.
Exclusion Criteria:
* Inability to provide informed consent.
* Presence of Crohn disease, IBD unclassified, non-IBD bowel conditions (e.g., celiac), or motility disorder.
* Presence of abnormal constrictions of the gastrointestinal tract, diseases of the esophagus and/or the superior opening of the stomach (cardia), potential or existing intestinal blockage, paralysis of the intestine, megacolon, fecal impaction, inflamed bowel or appendicitis, or have failed to defecate after taking another laxative.
* History of significant chronic disorders such as severe cardiac disease, malignancy requiring systemic chemotherapy or radiation therapy, significant renal failure, severe pulmonary disease, kidney disorders, diabetes, arthritis, multiple sclerosis, or other immune-mediated conditions requiring systemic therapy.
* Presence of serious infection (e.g., infectious colitis).
* Presence of severe anemia, defined as hemoglobin \<100 g/L or considered clinically significant based on physician discretion.
* Presence of disease or condition that negatively impacts ability to swallow, which may interfere with intake of supplement.
* Use of systemic antibiotics for more than a week during two months prior to intervention, or any antibiotic use during the intervention.
* Use of medications that inhibit peristaltic movement (e.g. opioids, loperamide)
* Consistent use of topical therapies (e.g., rectal suppositories, enemas) for at least a week, with a resulting improvement in symptoms (defined based on physician discretion).
* Use of probiotic, prebiotic, or fibre supplements in month prior to intervention or during the course of the trial that are known to affect the gut microbiome (if these are present in foods, such as yogurt or fermented foods, this will be allowed).
* Chronic use of laxatives, stool softeners, or anti-diarrheal medications.
* Chronic use of illicit drugs and/or excessive alcohol (e.g., average of \>7 drinks/week).
* Current smoker (cigarettes).
* History of abdominal surgery, including appendectomy.
* Pregnancy or intention of the patient to become pregnant during the study period.
* Breastfeeding.
* Allergy to any ingredients of investigational products or placebo (i.e., acacia gum, microcrystalline cellulose, or maltodextrin).
* Unable to maintain high fiber intake through supplementation during intervention.
