The average adult only eats 15 grams of fiber per day. Women need 25 grams of fiber per day, and men need 38 grams per day, according to the Institute of Medicine.Eating more plant foods -- vegetables, beans, fruit, whole grains, and nuts -- is the best way and is one of the major recommendations from the U.S. government's 2010 Dietary Guidelines.ating more plant foods -- vegetables, beans, fruit, whole grains, and nuts -- is the best way and is one of the major recommendations from the U.S. government's 2010 Dietary Guidelines.