Dietary fiber is carbohydrate from plant foods that is not fully digested in the small intestine and supports normal dietary variety. This page provides a definition and practical context; it is not an individualized medical or nutrition prescription. Use the related tools and guides for calculations or programming decisions rather than treating a glossary definition as a result.
Fiber’s practical role in a training diet
Most adults land well under the commonly cited target of roughly 25 to 38g of fiber per day, and closing that gap matters most in two situations common to people tracking macros: appetite control during a caloric deficit, where high-fiber foods add volume and satiety per calorie, and digestive comfort at higher food volumes during a calorie surplus, where fiber intake needs to rise alongside total food intake rather than staying fixed.
Increase fiber gradually rather than all at once. A sudden jump, especially alongside a big increase in water intake, commonly causes bloating and GI discomfort that settles within a week or two as intake stabilizes.
Where fiber comes from
Vegetables, fruit, legumes, and whole grains are the main sources, and spreading fiber intake across several of these categories tends to be easier on digestion than getting the same total from one concentrated source (a single large serving of beans or a fiber supplement, for example). Whole-food sources also bring water, micronutrients, and volume that a fiber supplement alone doesn’t replace.