Consumption of plant foods, including whole grains, vegetables, fruits, pulses, nuts, and seeds, is linked to improved health outcomes. Dietary fiber is a nutrient in plant foods that is associated with improved health outcomes, including a lower risk of chronic diseases such as cardiovascular disease, type 2 diabetes, and certain cancers. Different fibers deliver different health benefits based on their physiochemical properties (solubility, viscosity) and physiological effects (fermentability). Additionally, plant foods contain more than dietary fiber and are rich sources of bioactives, which also provide health benefits. The concept of the solubility of fiber was introduced in the 1970s as a method to explain physiological effects, an idea that is no longer accepted. Dividing total dietary fiber (TDF) into insoluble dietary fiber (IDF) and soluble dietary fiber (SDF) is an analytical distinction, and recent work finds that IDF intake is linked to a wide range of health benefits beyond increased stool weight. We have focused on the IDF content of plant foods and linked the concept of IDF to the bioactives in plant foods. Ancestral humans might have consumed as much as 100 g of dietary fiber daily, which also delivered bioactives that may be more important protective compounds in disease prevention. Isolating fibers to add to human diets may be of limited usefulness unless bioactives are included in the isolated fiber supplement.
Keywords: bioactives; dietary fiber; fruits; health; lignin; phytochemicals; plant foods; polyphenol; vegetables.