Irritable Bowel Syndrome - Symptoms & Causes

Extract from The Complete Guide to Food Allergy and Intolerance 2008 edition by Professor Jonathan Brostoff and Linda Gamlin

Irritable bowel syndrome, or IBS, is a very common problem characterized by pain in the lower abdomen, and some kind of change in bowel habits: constipation or diarrhoea, or switching between the two. The different forms of IBS are often classified into diarrhoea-predominant, constipation-predominant and alternating.

Pain (which is now regarded as the defining symptom of IBS) is often relieved by going to the lavatory or passing wind. The pain may come on when you eat a meal, because of a reflex - a perfectly healthy one that occurs in all of us - which stimulates movement in the bowels when you fill your stomach. In particular, it stimulates the progress, from the small bowel (small intestine) into the colon (large intestine or large bowel), of whatever is left from your last meal. The reflex occurs most strongly after high-fat meals. It is this movement of the intestines that is thought to provoke the meal-time pain in someone with IBS. The fact that the pain starts up when you eat doesn't mean that your IBS is necessarily due to food sensitivity.

Other symptoms that may occur in IBS are excessive wind, bloating, passing a clear mucus with the stools, straining to pass stools, urgency, or an uncomfortable feeling of incomplete evacuation - there being something still left in the rectum. There are other symptoms that often go together with IBS, including indigestion, urinary problems such as frequency or urgency, poor sleep, headaches, fibromyalgia, back pain, tiredness and depression. Women may experience painful periods (and their IBS pain may be worse just before a period), or pain after sexual intercourse.

Certain symptoms are not characteristic of IBS: diarrhoea that gets you out of bed at night, pain at night, fever, blood in the stools, and unexplained weight loss. If you have any of these you should see your doctor without delay because they can indicate a more severe type of bowel disorder.

There are no tests that can reliably show the presence of IBS, so the diagnosis is made on the basis of the patient's description of the symptoms. IBS is classed as a functional bowel disorder because there is no obvious underlying disease process - unlike Crohn's disease, for example, or ulcerative colitis or coeliac disease, where the inflammation in the gut is plain to see when the doctor looks inside with an endoscope, and where there are other tests, such as blood tests, that can indicate the presence of the disease (these diseases are classed as organic bowel disorders).

What causes irritable bowel syndrome?

A great many possible causes have been identified for IBS and it seems likely that several different things can go wrong to produce the symptoms. There is no agreement about what the most important cause is, or what might be the primary cause (ie the trigger that starts the whole problem off). You will find doctors who believe that it is more of a psychological disorder than a physical one, others who think that most cases are caused by gut flora imbalance in the colon (large bowel), or bacterial overgrowth in the small bowel, others who emphasize food sensitivity reactions, and yet others who think it's all due to some abnormality in the way the muscles of the gut move, or something wrong with the way nerve impulses from the gut are interpreted by the brain so that far more pain is felt from ordinary digestive events. There is some evidence to favour all of these.

The idea that there is low-grade inflammation of the gut lining in IBS has been slowly gaining ground over the past few years. This inflammation is nothing like as severe as that in Crohn's disease or ulcerative colitis, for example, and it isn't immediately obvious. It therefore escaped notice for a long time - and the fact that IBS was widely considered to be a largely psychological problem, or a pain-perception problem, did not encourage anyone to look more closely. Now, more and more research studies are being carried out in this area, and are finding increased levels of immune cells in the lining of the colon. In certain patients, those immune cells include mast cells, and together with other evidence this suggests that a small-scale localized IgE reaction may play a part in IBS for some people. There is also some evidence of a mild immune reaction against the gut flora in certain IBS patients.

It seems clear to us that IBS is not one single disease but a cluster of related problems. The different mechanisms that have been identified (see above) can all play some part, each adding to the effects of the others. For each individual IBS patient, the particular mix of causes is probably different.

This is an extract from Chapter 12 of The Complete Guide to Food Allergy and Intolerance 2008 edition by Professor Jonathan Brostoff and Linda Gamlin.

The chapter goes on to look in detail at a wide range of different dietary treatments for IBS, as well as considering drugs, antibiotics, probiotics, hypnotherapy and other forms of treatment.

The book also look at the value of the widely-advertised tests for identifying food intolerances in IBS. The Complete Guide to Food Allergy and Intolerance 2008 edition is available direct from Quality Health Books at www.quality-health-books.co.uk. The book costs £12.50. We offer free postage, a lowest-price guarantee (if you see it anywhere else for less, let us know and we'll refund the difference to you), a unique 6-month money-back offer (a full refund if the book hasn't helped you), and membership of the Quality Health Books Information Service which allows you to put questions to our medical experts.

The Complete Guide to Food Allergy and Intolerance also covers:

• Allergy and intolerance : what's the difference?
• Digestion, fibre, the gut flora. prebiotics and probiotics
• Tests for allergy and intolerance: which ones actually work?
• IgE food allergy
• Oral Allergy Syndrome (Pollen-Food Syndrome)
• Food reactions in asthma, eczema and allergic rhinitis
• Coeliac disease, Crohn's disease and eosinophilic conditions
• Food allergy impostors: false food allergy, and reactions to histamine, latex, mites, antibiotics, nickel and chromium in food
• Lactase deficiency and lactose intolerance
• Fructose, sucrose, sorbitol and xylitol
• Food intolerance
• Rheumatoid arthritis
• The elimination diet: a step-by-step guide
• Colic
• Sensitivity to cow's milk and other foods in babies
• Food sensitivity in children
• Checking food labels: synonyms for food ingredients
• Avoiding problem foods and alternatives to common foods
• Related foods - understanding food families
• Food additives
• Bottled water and water filters