Symptoms and Causes of Irritable Bowel Syndrome

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Irritable bowel syndrome (IBS) is a functional disorder of the colon (large intestine) that causes crampy abdominal pain, bloating, constipation, and/or diarrhea. IBS is classified as a functional gastrointestinal disorder because no structural or biochemical cause can be found to explain the symptoms. Upon diagnostic testing, the colon shows no evidence of diseases such as ulcers or inflammation. Therefore, IBS is diagnosed only after other possible digestive disorders and diseases have been ruled out.

IBS is often misdiagnosed or misnamed as colitis, mucous colitis, spastic colon, inflammatory bowel disease, or spastic bowel (colon). These misnomers persist, even though IBS is now a recognized and treatable condition. Affecting between 25 and 55 million people in the United States, IBS results in 2.5 to 3.5 million yearly visits to physicians. 20 to 40 percent of all visits to gastroenterologists are due to symptoms of IBS.


The symptoms of IBS can include:

Cramps are often relieved by a bowel movement, but some people with IBS may have cramps and be unable to pass anything. The severity of symptoms varies and could be anywhere from a mild annoyance to debilitating. Blood in the stool, fever, weight loss, vomiting bile, and persistent pain are not symptoms of IBS and may be the result of some other problem. IBS does not lead to any organic disease, such as Crohn’s disease or ulcerative colitis, or any type of bowel cancer.


Muscles in the colon normally contract a few times a day, moving feces along and ultimately resulting in a bowel movement. It is believed that in a person with IBS, these muscles are exceptionally sensitive to certain stimuli, or triggers.

Researchers are not certain exactly why the muscles in the colon of a person with IBS are more sensitive. However, IBS is not caused by stress or strong emotions. Some people have their first flare-up of IBS symptoms during a stressful period in their life such as the death of a relative or loss of a job. However, these stresses did not cause the condition but rather aggravated it to the point where it became more noticeable or bothersome.

The Different Forms of IBS

There are 3 different forms of IBS: Diarrhea-predominant (D-IBS), constipation-predominant (C-IBS), and alternating constipation and diarrhea (A-IBS). Symptoms of the different forms include:

  • D-IBS: abdominal discomfort or pain, urgency, and diarrhea
  • C-IBS: abdominal discomfort or pain, bloating and constipation
  • A-IBS: Intermittent symptoms of D-IBS and C-IBS


IBS is a diagnosis of exclusion, which means that organic diseases, infection, or other cause of the symptoms must be ruled out. In 1988 a group of physicians defined criteria to more accurately diagnose IBS. Known as the Rome Criteria, this set of guidelines that outlines symptoms and applies parameters such as frequency and duration make possible a more accurate diagnosis of IBS.

Symptoms in the Rome Criteria are not the only indicators of IBS. Extraintestinal symptoms include:

  • Nausea
  • Fatigue
  • Full sensation after even a small meal
  • Vomiting

Tests Used for Diagnosis

In addition to using the Rome Criteria, physicians may run several tests to ensure that there is no inflammation or infection in the body.

Blood tests. A blood test may be used to determine the white blood cell count or if anemia is present. A high white blood cell count gives physicians an indication that inflammation is taking place somewhere inside the body. Inflammation is not a symptom IBS.

Fecal occult blood test. This test can detect bleeding from almost anywhere in the digestive tract, even if it is not visible to the naked eye. Blood in the stool is not a symptom of IBS.

Stool culture. A physician may want to rule out other causes for diarrhea, such as a bacterial infection or parasite, with a stool culture. If any bacteria are found, the scientists can test it to determine what species it is and how best to treat it.

Barium enema. A barium enema (or lower gastrointestinal series) uses barium sulfate and air to outline the lining of the rectum and colon. Intestinal abnormalities may appear as dark silhouettes or patterns along the intestinal lining on the X-ray.

Sigmoidoscopy. A sigmoidoscopy is a way for a doctor to examine the last one-third of the large intestine. A biopsy may be taken during the procedure, which will be tested to help the physician determine the cause of any inflammation.

Colonoscopy. A colonoscopy is used to examine the inside of the colon beyond the areas a sigmoidoscopy can reach. Biopsies are taken during the test and patients are normally sedated or given "twilight sleep" so that they do not feel any pain.

Other tests may be used by physicians as needed to diagnose IBS or rule out other potential diagnoses.

Medications for Treatment

Several different types of drugs may be used to treat IBS. The goal of medication is to lessen troublesome IBS symptoms such as diarrhea, cramping, pain, or constipation.

Anticholinergics. This class of drugs affects the nerve cells or nerve fibers and are used to calm muscle spasms in the intestine and help symptoms of IBS such as cramping pain or diarrhea. 

  • Dicyclomine (Bentyl). Dicyclomine relaxes the muscles of the gut and bladder to prevent spasms and reduces the amount of stomach acid produced. Dicyclomine can be safely used long-term, under the guidance of a physician. Common side effects include constipation, dryness of mouth, nose, throat, or skin and a decreased ability to perspire (which can contribute to heat stroke).
  • Belladonna/Phenobarbital (Donnatal, Antispas, Barbidonna, Donnapine, Hyosophen, Spasmolin). This combination of two drugs is used to relax the muscles in the bladder and intestines as well as reduce stomach acid. Phenobarbital is a mild sedative can be habit-forming. Common side effects of belladonna/phenobarbital include a headache, nausea, constipation, rash, and vomiting. This drug may take 4 or 5 days to be effective, and, under the supervision of a physician, can be safely used long-term.
  • Hyoscyamine (Levsin, Anaspaz). This combination of two drugs, belladonna alkaloids, and barbiturates, is used to relax the muscles in the bladder and intestines as well as reduce stomach acid. Common side effects include a headache, nausea, constipation, rash, and vomiting. Hyoscyamine may be taken long-term under the guidance of a physician as long as side effects are absent or tolerable.
  • Chlordiazepoxide/clidinium (Librax). Chlordiazepoxide/clidinium prevents spams in the gut and also the bladder. Chlordiazepoxide is a sedative and may be habit-forming. Common side effects include bloated feeling, decreased sweating, dizziness, drowsiness, dryness of mouth, and headache. This drug may take 4 or 5 days to be effective, and, under the supervision of a physician can be safely used long-term.

Antidiarrheals. Antidiarrheals are used to slow down the effect of the bowel. These drugs may be used to prevent diarrhea that occurs from IBS.

  • Diphenoxylate/atropine (Lomotil). The diphenoxylate portion of this drug is used to treat diarrhea, while the atropine relieves muscle spasms in the gut. Common side effects include a headache, dizziness, drowsiness, blurred vision, dry mouth, and constipation. Although it is not a narcotic, diphenoxylate is derived from narcotics and may be mildly habit-forming. Diphenoxylate/atropine is typically prescribed to control diarrhea in the short-term and is not recommended for long-term use.
  • Alosetron hydrochloride (Lotronex). This drug is only used to treat women with severe D-IBS. Alosetron hydrochloride was approved and then pulled from the market by the FDA after several cases of serious side effects in women taking it. It is now only approved for use on a limited basis. Alosetron hydrochloride disrupts the action of serotonin, a chemical in the body that has an effect on intestinal movement and pain. Treatment usually begins with a 4-week trial and may be continued for another 4 weeks under the supervision of a physician.

    Supplements to Help With Symptoms

    Many people with IBS may turn to supplements to augment or replace traditional medical therapy. There are supplements that may help with IBS symptoms, yet it is important to note that they may also have side effects, and their use should always be reported to physicians like any prescription drug.

    Acidophilus. Acidophilus is the “good bacteria” that live in your colon. A supplement can help the healthy gut bacteria grow while reducing the harmful bacteria. Fructo-oligosaccharides (FOS) may be added to acidophilus pills. FOS are carbohydrates that are not digestible by humans, but serve to help the beneficial bacteria to grow. Acidophilus comes in a capsule form, and the bacteria must be alive to be effective.

    Chamomile. Chamomile is a known anti-spasmodic and can soothe the muscles in the digestive tract. While no human studies have been performed on this supplement in relation to IBS, it has been proven to reduce irritation and cramping in animals. Chamomile can be taken as a tea, or as a capsule.

    Ginger. Ginger has long been known to help with nausea, and may also be helpful in stimulating peristalsis and reducing painful cramps. Ginger may be taken as a tea, a capsule, or even in food.

    Peppermint Oil. Peppermint can relax muscles throughout the digestive tract. This does help reduce spasms in the colon, but it can also relax the lower esophageal sphincter and cause heartburn or exacerbate gastroesophageal reflux disease. Peppermint oil can be taken in either capsule or tea form. While they are most effective, capsules may cause anal irritation.

    Alternative And Complementary Therapies

    Hypnosis. A ground-breaking study in 1984 showed that IBS patients treated with hypnotherapy demonstrated not only significant improvement in their symptoms but also did not suffer relapses during the 3 month study period. Gut Directed Hypnotherapy was developed specifically for IBS patients and has been proven to reduce symptoms in 80% of cases.

    Cognitive Behavior Therapy. Behavior therapy helps redefine the associations between worrisome circumstances and a person’s typical reaction to them. Cognitive therapy examines the relationship between thoughts and symptoms. Together these two treatments are known as cognitive behavior therapy (CBT). Therapy may begin with a diary of IBS symptoms, then move on to biofeedback, positive self-talk, and reducing negative responses to stress.

    How Diet Affects IBS

    While foods do not cause IBS, eating certain foods, called "trigger foods" may set off symptoms of diarrhea, bloating, or pain. Unfortunately, there is no one diet that will work for all people with IBS, but there are some guidelines that may help.

    Eating several smaller meals during the day, rather than three large ones may help to reduce symptoms (large meals may result in cramping and diarrhea). Additionally, it may be helpful to keep meals low in fat and high in carbohydrates such as whole-grain breads, pasta, rice, fruits, vegetables, and cereals. A low fat, high protein diet may also help with pain experienced after eating.

    Common trigger foods include:

    • Alcohol
    • Artificial sweeteners or sugar substitutes
    • Artificial fat (Olestra)
    • Carbonated beverages
    • Coconut milk
    • Coffee (even decaffeinated)
    • Dairy
    • Egg yolks
    • Fried Foods
    • Oils
    • Poultry skin and dark meat
    • Red meat
    • Shortening
    • Solid Chocolate

    Soluble fiber has several benefits that may also reduce symptoms of IBS. Fiber may prevent spasms because it keeps the colon somewhat distended. It also absorbs water, which helps to keep stools from being too hard and therefore difficult to pass. Initially switching to a high fiber diet may increase gas and bloat, but these symptoms should decrease in a few weeks as the body adjusts.

    Supplements may be helpful in adding the necessary fiber to the diet. There are three main types of soluble fiber supplements (psyllium, methylcellulose, and polycarbophil) and each has varying uses, side effects, and properties.

    Reducing the intake of foods that cause intestinal gas may help in decreasing bloating. Chewing gum increases gas in the body, as does swallowing air while eating (which can occur when gulping liquids or talking while eating). Carbonated beverages (such as soda pop or sparkling water) can also lead to bloating and intestinal gas (as well as belching).

    Food Sensitivities

    Some people with IBS may also have food sensitivities. Food sensitivity is different than a true food allergy, so it may not be detected in traditional allergy tests. Some of the more common causes of food sensitivity include:

    • Sorbitol (a sugar substitute)
    • Fructose (found in fruit juice and dried fruit)
    • Lactose (found in milk)
    • Wheat bran

    Lactose intolerance is a common condition that is the result of the body's inability to digest lactose or milk sugar. Symptoms include gas, bloating, and sometimes even pain. If lactose intolerance is suspected, avoidance of milk and milk products should reduce symptoms.

    Finding Your IBS Trigger Foods

    Keeping a food and symptom diary is a good way to trace foods that lead to IBS attacks. The food diary should include not only time and foods eaten, but also where they were eaten, and frame of mind or mood. It is important to include every food (even the candy you eat from the bowl on your co-worker’s desk) and how it was prepared (i.e. "fried chicken", not just "chicken"). The diary should be filled out several times a day so nothing is forgotten. After several weeks, a physician or dietician can help in reviewing the diary to find trigger food patterns.

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