Psyllium fiber, derived from the husks of Plantago ovata seeds, is primarily known as a bulk-forming laxative and is widely used to manage constipation and promote overall gut health. There is moderate scientific evidence supporting its use in the management of ulcerative colitis (a major form of colitis), particularly during remission phases. Several clinical studies have shown that psyllium can help maintain remission in patients with ulcerative colitis. For example, a randomized controlled trial published by Fernandez-Banares et al. (Gut, 1999) demonstrated that psyllium was as effective as mesalazine, a standard medication, in maintaining remission in ulcerative colitis patients. The proposed mechanisms include psyllium's ability to increase stool bulk, improve gut motility, and produce short-chain fatty acids like butyrate during fermentation, which have anti-inflammatory effects on the colon mucosa.

However, the evidence is not robust or universal. Most research has focused on ulcerative colitis rather than all forms of colitis, and the number of high-quality, large-scale studies is limited. Psyllium is generally well-tolerated, but it can cause bloating or discomfort in some individuals. It is important to note that psyllium should be used with caution during active flare-ups, as adding fiber can sometimes exacerbate symptoms in those with severe inflammation or narrowing of the colon. Overall, psyllium fiber is supported by moderate scientific evidence for maintaining remission in ulcerative colitis, but it should not replace standard therapies or be used during acute disease phases without medical supervision.