Diversity of fibers in common foods: Key to advancing dietary research

Dietary fibers are plant-derived carbohydrates and associated components, that are not digested within the human upper intestinal tract/gut. Traditionally they are classified based on their solubility in water i.e., soluble dietary fiber (SDF) and insoluble dietary fiber (IDF). The SDFs are generally regarded as fermentable by the microbiota, primarily within the large intestine. Dietary fibers are considered health-promoting food components that have profound impacts on different diseases such as diabetes, cancer, cardiovascular, and inflammatory bowel diseases. Although the majority of studies published to date have examined low fiber or high fiber in diets, or soluble versus insoluble fiber at best, the functionality of dietary fiber subtypes has been proven beyond those definitions. These subtypes include β-fructans, β-glucans, pectin, arabinoxylans, etc., which are further subdivided, and each differs in its molecular structure, composition, and functions, which have unfortunately been largely overlooked to date, particularly in clinical research. Inconsistent evidence regarding dietary fibers is brought on by a combination of variable measurement methods and unreliable documentation of fiber sources in manuscripts (e.g., ripeness, cultivar, growing conditions). This highlights the importance of expanding knowledge to explore dietary fiber subtypes and the complexity of their individual interactions with both host and microbiota within the human gut and beyond. This study will review the quantified content of dietary fiber subtypes elucidated by biochemical research studies to develop a readily accessible platform for future nutritional studies.