This month's Nutrition Action Healthletter is all about fiber. Fiber is great stuff. Not only because it helps you stay regular, but foods high in fiber tend to be more filling. Fiber is found in carbohydrate sources of food. Simply put, it's the part of the grain or plant that is not able to be digested by the body. There are 2 natural types of fiber: soluble & insoluble. 
If you've ever taken Metamucil or psyllium husk, you've taken Soluble fiber; it gets gel like when it interacts with water. Because of that, when you eat foods that are high in soluble fiber, it bulks up in your stomach causing you to feel less hungry.
Insoluble fiber is found in the bran part of whole grains, and in most vegetables as well as edible fruit skins. Insoluble fiber stimulates the muscles of the large intestine, helping the waste with it pass through the body more rapidly.
Remember a few years back when all the rage on marketing of processed foods was "Net Carbs"? What food manufacturers were doing was removing the fiber values from the total carbohydrate sum to give you the total number of digestible carbohydrates in the food source. This is actually accurate, since we don't digest fiber, we don't consume the number of calories that fiber contains: 4 per gram.
Additionally, it's been shown that when eaten in the right doses, fiber can bind to fat in the digestion process, therefore lowering the number of calories that the body absorbs even further.
Current recommendations for fiber are 20-25 grams of fiber daily for women and 30-35 grams of fiber daily for men. The more fiber you can get into your diet the better; however it's best to introduce your body to it slowly if you haven't been paying attention to your intake until now.