Insoluble and soluble fiber are both not digested by the body. They are both excreted by our body. The difference is that insoluble fiber passes through the body basically in the same condition as it entered our body.
Insoluble fiber (fruit skins, cauliflowers, green beans, potato skins, whole wheat products, corn bran, etc. are needed to prevent constipation and balance the acidity in the intestines. Soluble fiber (oranges, apples, carrots, nuts, oat bran, etc.) helps the body to more slowly release sugar and it binds with fatty acids.
The average diet should contain both fibers. However, some foods contain both; such as flax seed and psyllium husk. The most important dietary concern is to get 25 grams of fibers a day. Eating the recommended 6 servings of grain products (be sure to include whole grains) and 5 servings of fruits and vegetables should help you to meet the 25 grams.
At the Harvard School of Public Health, fiber is further defined as the carbohydrates that cannot be digested. This website also has an extensive list of soluble and insoluble fiber. This site recommends 20-35 grams and notes that the average American eats only 14-15 grams of dietary fiber daily.
The Harvard School lists these tips for increasing fiber intake:
1) Eat whole fruits instead of fruit juices.
2) Replace white rice, bread, and pasta with brown rice and whole-grain products.
3) Choose whole-grain cereals for breakfast.
4) Snack on raw vegetables instead of chips, crackers, or chocolate bars.
5) Substitute legumes for meat 2-3 times per week in chili and soups.
6) Experiment with international dishes (such as Indian or Middle Eastern) that use whole grains and legumes as part of the main meal (as in Indian dahls) or in salads (for example, tabbouleh).
You The Owner’s Manual (one of the books in the Changemaker Weight Loss Library) lists the following foods with fiber count for each: apple (3.5 grams—eat with skin), banana (2 grams), orange (1.2 grams), sweet potato (1/2 cup-3 grams), kidney beans (1/2 cup cooked-7.3 grams), lima beans (1/2 cup cooked-4.9 grams), brown rice (1/2 cup-2.4 grams), whole wheat spaghetti (1 cup-3.9 grams), figs (3 medium-5.3 grams, and broccoli (1/2 cup-2.3 grams. The authors recommend snack on dried fruit, such as apricots, figs, prunes, or raisins, for nutrition and fiber.