A good way to understand the difference between soluble and insoluble fiber is to know what happens when each one interacts with water in the digestive system.
Soluble fiber dissolves in water to become a gel, which slows digestion. It may help promote normal blood cholesterol levels and blood glucose levels. Common sources are oat bran, oatmeal, barley, nuts, seeds, beans, lentils, peas, and some fruits and vegetables.
Insoluble fiber does not dissolve in water. It speeds the movement of food through the digestive system, which helps promote regularity. Common sources are wheat bran, bran cereals, whole-wheat breads and pastas, and some fruits and vegetables.
As you know from your cereal label, some foods contain a mix of both types of fiber—and both types are important for good health.
Health authorities don't give specific recommendations for how much soluble versus insoluble fiber to consume. So, the best tactic is to eat a variety of fiber-containing foods to meet your daily total fiber recommendation.
For instance, the daily recommendation for women age 19 - 50 is 25 grams and for men is 38 grams. For those over 50, it's 21 grams for women and 30 grams for men.