Polyphenols are a diverse group of naturally occurring compounds found abundantly in fruits, vegetables, tea, coffee, and other plant-based foods. Their use to support the small intestine is primarily justified by scientific evidence, although this area is still evolving. Several studies have shown that polyphenols possess anti-inflammatory, antioxidant, and prebiotic properties that can benefit intestinal health. For example, research indicates that polyphenols can modulate the gut microbiota, enhancing populations of beneficial bacteria such as Lactobacillus and Bifidobacterium species, which are important for maintaining intestinal barrier function and reducing inflammation.

Polyphenols such as flavonoids, phenolic acids, and tannins can also inhibit the growth of pathogenic bacteria, protect the intestinal lining from oxidative stress, and reduce markers of inflammation in the gut. Some human and animal studies suggest that polyphenols may support the integrity of the intestinal barrier, reducing the risk of "leaky gut" and associated symptoms. However, most of the evidence comes from cell culture studies, animal models, and a limited number of human clinical trials, and results can vary depending on the type and dose of polyphenol.

While more high-quality, large-scale human studies are needed, current scientific evidence supports a moderate role for polyphenols in promoting small intestine health, primarily through their effects on gut microbiota and inflammation.