Foods high in insoluble fiber include wheat bran, vegetables, and whole grains. It thickens the stool and appears to aid in the passage of food through the stomach and intestines. Insoluble fiber doesn't dissolve in water, so it moves through your digestive system undigested. Soluble fiber is found in oats, peas, beans, apples, citrus fruits, carrots, barley, psyllium, and fruit juices. When soluble fiber dissolves in water, it forms a gel that absorbs moisture and increases stool bulk. Soluble fiber also promotes the absorption of minerals such as calcium and magnesium from the digestive system. For these reasons, adding more soluble fiber to your diet can be beneficial for reducing cholesterol levels and preventing kidney stones. Insoluble fiber does not dissolve in water; instead, it increases stool bulk. Increasing your daily intake of insoluble fiber may help reduce your risk of developing kidney stones, diabetes, and heart disease. The American Cancer Society recommends that men should eat 20 grams of fiber per day and women should eat 38 grams per day. Fruits, vegetables, and whole-grain products are all good sources of fiber. Wheat bran, corn bran, and oat bran are all examples of insoluble fiber. They can be added to bread, pasta, or other dishes that contain flour as a thickener or seasoning.