Black psyllium (Plantago indica, also known as Blond psyllium for Plantago ovata or Black psyllium for Plantago psyllium) is a source of soluble fiber commonly used to manage various gastrointestinal disorders, including constipation and irritable bowel syndrome. Its use in diverticulitis or diverticular disease is supported by some clinical and mechanistic evidence, though the strength of evidence is modest and largely extrapolated from its effects on general bowel health.

The rationale for using psyllium fiber in diverticular disease (not acute diverticulitis) is to soften stool and promote regular bowel movements, thereby reducing colonic pressure and potentially preventing the formation of new diverticula or complications. Several guidelines and reviews (e.g., American Gastroenterological Association, 2015) mention fiber supplementation for symptomatic uncomplicated diverticular disease, but specific high-quality randomized controlled trials on psyllium for diverticulitis are lacking. Most clinical studies focus on fiber as a broad category, not specifically on black psyllium, and evidence for preventing recurrence or reducing symptoms is mixed.

In summary, while there is some scientific rationale and limited clinical evidence supporting the role of psyllium fiber in managing diverticular symptoms, the evidence is not robust, and its use is better supported for diverticular disease maintenance rather than acute diverticulitis. The rating reflects the limited but present scientific validation for this use.