Over millions of years of human evolution, dietary fber (fber) has played an important role in maintaining healthy colonic microbiota and laxation, energy and cardiometabolic processes, and immune and inflammatory signaling required for human health and chronic disease prevention. • It is estimated that approximately 95% of populations consuming Western diets eat an inadequate daily fber level. This fber gap can adversely affect human health via increased risk of weight gain and dysfunctional colonic microbiota, contributing to global obesity and chronic disease pandemics. • Fiber comes from whole or minimally processed plant foods including whole grains, fruits, vegetables, legumes, nuts, and seeds eaten as part of a healthy diet; isolated from natural sources (e.g., β-glucan, psyllium); or from synthetic forms (e.g., polydextrose, methylcellulose) added to processed foods or consumed as dietary supplements. Fiber food functionality or health effects depend on the specifc fber's composition, physical properties, and degree and rate of fermentation in the colon. • The effects of increased fber intake and its fermentation metabolites can result in reduced risk of obesity, cardiometabolic chronic diseases and related premature mortality, and improved odds for healthy aging. • No tolerable upper limit has been set for fber intake in healthy individuals, but excessive intake of some highly fermentable fbers may increase risk of flatulence and gastrointestinal distress in sensitive individuals. When increasing fber intake, it is recommended to do so gradually along with increasing fluid intake to help allow the gastrointestinal tract to adapt and to take medication at least 1 h before or 2 h after fber-rich foods or supplements are consumed to avoid possible fberdrug interactions.