Soluble fiber dissolves in liquid and insoluble fiber absorbs liquid. Insoluble fiber can absorb up to 15 times its weight in water as it moves through the digestive tract. It is important to consume adequate amounts of liquids along with fiber, particularly with products containing dry fiber such as supplements or dry cereals. Their requirements are less than for adults. For children, ages 3 to 18, the American Dietetic Association reports a formula for determining recommended fiber intake - a child's age plus five equals the grams of dietary fiber he or she should eat daily.
Good sources are fruits, vegetables, and whole grains.
As with anyone increasing dietary fiber, it is important to drink extra liquids such as water, juice, or milk. Although relatively rare, food allergies to certain foods can also mimic or exacerbate symptoms of functional GI disorders. Allergies can also lead to more generalized symptoms involving skin rashes, asthma, and swelling. Food intolerance occurs when the body cannot adequately digest a portion of a particular food, usually because of a chemical deficiency. For example, people with lactose intolerance have difficulty digesting milk because of a deficiency of the enzyme lactase.