Loose bowel motions may be due to an infection (gastroenteritis) but if the symptoms persist for more than 3 weeks then other conditions need to be considered. Sometimes the problem is......

Diet for IBS

There is no easy way to identify which food if any is causing the IBS symptoms

Diet for irritable bowel syndrome

  • Irritable bowel syndrome has no definable cause but there are clearly some triggers that aggravate the condition.
  • The main triggers are:
    • Stressful life events.
    • Food triggers.
    • Gastroenteritis infections - can be the starting event or an aggravating factor
  • Altering the diet is always going to be the easiest approach to reducing these "triggers" but approaches towards reducing stress should also be explored.
  • The majority of food triggers are best described as an intolerance rather than food allergy.
  • Genuine food allergy as a cause of IBS is probably uncommon.
    • Food allergy causes rapid onset of itching, swelling of lips, tightness in throat and wheezing.
    • 90% of food-related allergic problems are caused by  milk, eggs, peanut, soy, other nuts, fish, shellfish.
  • The mechanism by which foods aggravate IBS is unclear.
    • It probably involves events in the lumen of the bowel rather than any inflammatory or immune response of the bowel wall.
    • This means that the symptoms may be due to foods that were consumed over the past 1-3 days - not just the last meal.
    • "Intolerance" may occur for larger helpings of a particular food but not with smaller amounts. This is different from a genuine allergy where even small amounts can cause symptoms within a few hours.
    • Colonic fermentation is probably an important mechanism. This depends on the type of bacteria in the colon AND the type of food AND the speed of transit through the colon.
    • Fermentation and gas production is increased in people with irritable bowel.
  • For example the exclusion of wheat from the diet is a common recommendation (and is often helpful).
    • This benefit can be demonstrated in people who do not have the immune-based disease of coeliac disease (gluten-sensitive enteropathy).
    • The mechanism by which wheat aggravates IBS is debated - it may be because of higher fermentation levels (gas production) in the colon with wheat compared with rice.
    • Increased levels of gas production in people with IBS is a problem because the gut more sensitive to "stretch" from trapped wind
    • Recent studies have broadened the debate.  There may be other mechanisms by which gluten can exert harmful effects on the gut (different from the immune-mediated coeliac disease and not related to excess fermentation)
    • It is seems likely that a low carbohydrate diet is effective  - this is a more radical approach and could have some long-term harmful effects  i.e higher risk of heart disease if animal fats and protein are markedly increased. 
  • The most diets that have been developed for IBS have come from extensive questionnaires rather than from any direct scientific study.
    • There is no easy shortcut to finding out what are the aggravating foods. Skin prick tests and blood tests for allergy have proven to be disappointing.
    • The suggestions for "allowed" and "not allowed" (in the exclusion table are simply those foods that are prominent in dietary surveys of people with IBS.
    • The recent promotion of a FODMAP diet is partly driven by science  - that is careful analysis of food composition looking for poorly absorbed carbohydrates.  The concept that this malabsorption is the key problem in IBS is hypothesis only but the results of this diet are very good. 
    The strict approach is too have a very restricted diet for 2-4 weeks and then gradually add in foods one by one. This is called an exclusion diet. This is straightforward concept but difficult too achieve in practice. The underlying variability of IBS makes any improvement or deterioration difficult to interpret. These negative and discouraging comments shouldn’t detract from the main message.
    • Food triggers are common.
    • If identified, exclusion of particular foods can make a long-term difference to quality of life with IBS.
    • Food exclusion is always a more preferred option to taking prescribed medications for IBS and of course has no long term side-effects.


  • The main risk from an exclusion diet is developing an inappropriately strict approach to food exclusions that may not necessarily to be required.
    • Potentially leading to weight loss!
    • To an unhealthy obsession with what can and can't be consumed.
    • Possibly heightened stress with regard to food choices.
  • There are some foods that cause problems for most people with IBS but there are also unique issues for any individual.


  • Recommended recipe book

    "Irresistables for irritables" by Sue Shephard
    Available through Pathfinder Bookshop 0800 55 44 55
  • Low FODMAP cooking book available from www.shepherdworks.co.au


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