Pectin and cellulose are both types of dietary fiber found in plant cell walls. In the context of Irritable Bowel Syndrome (IBS), their use is supported by a moderate level of scientific evidence, particularly for symptom management. Pectin is a soluble fiber, which can form a gel-like substance in the gut and has been shown to help regulate bowel movements and soften stool, potentially easing both constipation and diarrhea associated with IBS. Several clinical studies have indicated that certain soluble fibers (notably psyllium, but also pectin) can improve global symptoms and abdominal pain in IBS patients. Cellulose, on the other hand, is an insoluble fiber, which adds bulk to stool and may help some individuals with constipation-predominant IBS, though it is generally less favored over soluble fibers due to a potential to worsen bloating in sensitive individuals.

Overall, the American College of Gastroenterology and other guideline-issuing bodies currently recommend soluble fiber supplementation (such as pectin) as a therapeutic option for IBS, while being more cautious about the use of insoluble fiber (like cellulose), due to the risk of exacerbating symptoms. The evidence base consists of meta-analyses and randomized controlled trials, but the effect size is moderate and responses are individualized. Thus, while pectin-cellulose preparations are scientifically validated for use in some patients with IBS, the evidence is not unequivocal, and fiber interventions should be tailored to individual tolerance and symptom pattern.