Fiber blends, typically consisting of a mixture of soluble and insoluble dietary fibers from sources like psyllium, oat bran, apple pectin, and others, are scientifically supported for their beneficial effects on the small intestine and overall digestive health. Multiple studies have demonstrated that dietary fiber can improve intestinal motility, regulate bowel movements, and support the growth of beneficial gut microbiota, all of which have a positive impact on the small intestine's function.

Soluble fibers serve as prebiotics, providing nourishment for beneficial bacteria, which ferment these fibers into short-chain fatty acids (SCFAs) like butyrate. SCFAs play a crucial role in maintaining the health of the intestinal mucosa and modulating inflammation. Insoluble fiber, on the other hand, adds bulk to stool and can help prevent constipation, ensuring that waste moves efficiently through the small and large intestines. There is also evidence indicating that adequate fiber intake can reduce the risk of developing certain gastrointestinal disorders, such as diverticulosis and irritable bowel syndrome (IBS).

Most major health organizations, including the World Health Organization and the American Gastroenterological Association, recommend sufficient daily fiber intake for supporting digestive tract health, which includes the small intestine. However, while fiber clearly supports digestive health, specific effects isolated to the small intestine (as opposed to the digestive system as a whole) are less well studied, hence a rating of 4 rather than 5.