Plant fibers have important influences on gastrointestinal physiology and the absorption of many nutrients. Certain fibers delay the absorption of carbohydrates and result in less postprandial hyperglycemia. Because the intake of plant fibers lowers plasma glucose concentrations and decreases glycosuria, high-fiber foods may be useful in the management of diabetes mellitus. Consumption of selected fibers and fiber-rich foods lowers serum cholesterol values and may lower triglyceride concentrations. Plant fiber intake may lead to mineral depletion or vitamin deficiency, but this has not been observed in several long-term studies. Further work is required to delineate the therapeutic utility of plant fibers in the diet of persons with diabetes and to assess the undesirable effects of fiber intake. In our opinion, persons with diabetes who are eating very low-fiber diets would benefit from an increase in plant fiber intake from whole grains, legumes, and vegetables.