There are two types of fiber: soluble fiber and insoluble fiber. Soluble fiber adds volume to the feces. Soluble fiber is found in foods such as apples, bananas, barley, oats, and beans. Insoluble fiber aids in the transit of food through the digestive tract and aids in the prevention of constipation. Insoluble fiber is found in wheat bran, whole-wheat flour, corn bran, and vegetables such as cauliflower, green beans, and potatoes. The amount of fiber you need each day varies depending on your age, gender, height, weight, lifestyle, and medical condition. For example, if you're pregnant or trying to get pregnant, your doctor may recommend increasing your daily fiber intake. The American College of Obstetricians and Gynecologists recommends that women between 18 and 50 years old eat at least 25 grams of fiber every day. Women over 50 should consume at least 30 grams of fiber daily. The same amount for men would be 45 to 60 grams per day. Fiber comes from plants. There are three main types of fiber: cellulose, hemicellulose, and lignin.