I used to suffer from constipation when I was younger.  Pregnancy and childbirth had also caused me to have piles.  One natural food that I find really effective in keeping constipation and piles at bay is psyllium husk. I take a tablespoon of psyllium husk everyday.  Psyllium husk is fibre and is not toxic to the body.  One should drink LOTS of water after consuming psyllium husk.

How to prevent constipation :

Eat fiber regularly.
Choose lots of high-fiber foods, including fruits, vegetables, beans and whole-grain cereals and breads. Experiment to see if particular fruits or vegetables have a laxative effect for you. Adding fiber to your diet gradually may help reduce gas and bloating.

Limit problem foods
Foods that are high in fat and sugar and those that tend to be low in fiber content, such as ice cream, cheese and processed foods, may cause or aggravate constipation.

Drink plenty of liquids.
The exact amount of water and other fluids you should drink each day varies and depends on your age, sex, health, activity level and other factors.

Increase your physical activity.
Engage in regular exercise, such as walking, biking or swimming, on most days.

Heed nature’s call.
The longer you delay going to the toilet once you feel the urge, the more water that’s absorbed from stool and the harder it becomes.

Try fiber supplements.
Over-the-counter products such as Metamucil and Citrucel can help keep stools soft and regular. Check with your doctor about using stool softeners. If you use fiber supplements, be sure to drink plenty of water or other fluids every day. Otherwise, fiber supplements may cause constipation or make constipation worse.
Add fiber to your diet slowly to avoid problems with gas.

Don’t rely on stimulant laxatives.
These include products such as Correctol and Dulcolax, which cause muscle contractions in the intestines. Habitual use can damage your bowels and make constipation worse. For occasional relief try saline laxatives, such as milk of magnesia. Saline laxatives draw water into the colon to allow stool to pass easier. Keep in mind that long-term use of laxatives can cause dependency. For constipated children, give them plenty of fluids to drink, but avoid giving them laxatives unless your doctor says it’s OK.