To understand constipation, it helps to know how the colon (large intestine) works. As food moves through the colon, it absorbs water while forming waste products, or stool. Muscle contractions in the colon push the stool toward the rectum. By the time stool reaches the rectum, it is solid because most of the water has been absorbed.

The hard and dry stools of constipation occur when the colon absorbs too much water or if the colon's muscle contractions are slow or sluggish, causing the stool to move through the colon too slowly. Common causes of constipation include the following.

Not Enough Fiber in the Diet
The most common cause of constipation is a diet low in fiber found in vegetables, fruits, and whole grains and high in fats found in cheese, eggs, and meats. People who eat plenty of high-fiber foods are less likely to become constipated.

Dietary fiber provides the bulk that helps to speed the passage of waste food through the bowel. Lack of fiber results in harder, more compact stools, which take longer to pass through. Fiber--both soluble and insoluble--is the part of fruits, vegetables, and grains that the body cannot digest. Soluble fiber dissolves easily in water and takes on a soft, gel-like texture in the intestines. Insoluble fiber passes through the intestines almost unchanged. The bulk and soft texture of fiber help prevent hard, dry stools that are difficult to pass.

A low-fiber diet also plays a key role in constipation among older adults, who may lose interest in eating and choose convenience foods low in fiber. In addition, difficulties with chewing or swallowing may force older people to eat soft foods that are processed and low in fiber.

Not Enough Liquids
Lack of fluids - The body needs 1.5 - 2 quarts a day to function efficiently. Without sufficient fluids, waste matter dries out, making it harder to move through the bowel. Liquids like water and juice add fluid to the colon and bulk to stools, making bowel movements softer and easier to pass. People who have problems with constipation should drink enough of these liquids every day, about eight 8-ounce glasses. Liquids that contain caffeine, like coffee and cola drinks, and alcohol have a dehydrating effect.

Changes in Life or Routine
During pregnancy, women may be constipated because of hormonal changes or because the heavy uterus compresses the intestine. Aging may also affect bowel regularity because a slower metabolism results in less intestinal activity and muscle tone. In addition, people often become constipated when traveling because their normal diet and daily routines are disrupted.

Abuse of Laxatives
Myths about constipation have led to a serious abuse of laxatives. This is common among people who are preoccupied with having a daily bowel movement.

Laxatives usually are not necessary and can be habit-forming. The colon begins to rely on laxatives to bring on bowel movements. Over time, laxatives can damage nerve cells in the colon and interfere with the colon's natural ability to contract. For the same reason, regular use of enemas can also lead to a loss of normal bowel function.

Ignoring the Urge to Have a Bowel Movement
People who ignore the urge to have a bowel movement may eventually stop feeling the urge, which can lead to constipation. Some people delay having a bowel movement because they do not want to use toilets outside the home. Others ignore the urge because of emotional stress or because they are too busy. Children may postpone having a bowel movement because of stressful toilet training or because they do not want to interrupt their play.

Lack of Exercise
Lack of exercise can lead to constipation, although doctors do not know precisely why. For example, constipation often occurs after an accident or during an illness when one must stay in bed and cannot exercise.

Irritable Bowel Syndrome (IBS)
Some people with IBS, also known as spastic colon, have spasms in the colon that affect bowel movements. Irritable bowel syndrome (IBS) sufferers often have constipation, sometimes alternating with diarrhea. In IBS, cramping pains and discomfort in the bowel and rectum are common. Constipation and diarrhea often alternate, and abdominal cramping, gassiness, and bloating are other common complaints. Although IBS can produce lifelong symptoms, it is not a life-threatening condition. It often worsens with stress, but there is no specific cause or anything unusual that the doctor can see in the colon.

Medications
Some commonly used medicines are known to cause constipation, particularly certain painkillers (e.g. codeine), iron tablets and some antacids (e.g aluminium hydroxide). They include:

• pain medications (especially narcotics)
• antacids that contain aluminum and calcium
• blood pressure medications (calcium channel blockers)
• antiparkinson drugs, antispasmodics and antidepressants
• diuretics
• anticonvulsants