Cant be bothered to write so im just cutting and pasting.
The American Dietetic Association (ADA) recommends a minimum of 20-35 g/day for a healthy adult depending on calorie intake (e.g., a 2000 cal/8400 kj diet should include 25 g of fiber per day). The ADA's recommendation for a child was that intake should equal age in years plus 5 g/day for children (e.g., a 4 year old should consume 9 g/day). No guidelines have yet been established for the elderly or very ill. Patients with current constipation, vomiting, and abdominal pain should see a physician. Certain bulking agents are not commonly recommended with the prescription of opioids because the slow transit time mixed with larger stools may lead to severe constipation, pain, or obstruction.
The British Nutrition Foundation has recommended a minimum fiber intake of 12-24 g/day for healthy adults
Fiber is in...
legumes (peas, soybeans, and other beans)
oats
some fruits (particularly apples, bananas), and berries
certain vegetables, such as broccoli and carrots
root vegetables, such as potatoes and yams (the skins are insoluble fiber)
psyllium seed (only about ⅔ soluble fiber).
Legumes also typically contain shorter-chain carbohydrates that are indigestible by the human digestive tract but which are digested by bacteria in the large intestine (colon), which is a cause of flatulence.
Sources of insoluble fiber include
whole grain foods
bran
nuts and seeds
vegetables such as green beans, cauliflower, zucchini, celery
the skins of some fruits, including tomatoes
More info
http://en.wikipedia.org/wiki/Dietary_fiber