Microbiota-dependent and -independent effects of dietary fiber on human health

Dietary fiber, such as indigestible oligo- and polysaccharides, occurs in many foods and has gained considerable interest related to its beneficial effects on host health and specific diseases. Dietary fiber is neither digested nor absorbed in the small intestine and modulates the composition of the gut microbiota. New evidence indicates that dietary fiber also directly interacts with the epithelium and immune cells throughout the gastrointestinal tract by microbiota-independent effects. This review provides a focused overview of how dietary fiber improve human health and how these reported health benefits are connected to molecular pathways, in (1) a microbiota-independent manner, via interaction with specific surface receptors on epithelial and immune cells regulating intestinal barrier and immune function, (2) a microbiota-dependent manner via maintaining intestinal homeostasis by promoting beneficial microbes, including Bifidobacteria and Lactobacilli, limiting the growth, adhesion and cytotoxicity of pathogenic microbes, as well as stimulating fiber-derived microbial short-chain fatty acid production.