IBS - Should you restrict your diet to relieve symptoms?

Updated: Jul 6, 2019


Irritable bowel syndrome (IBS) is one of the most frequent causes of referral to the gastroenterologist. It is a combination of chronic and recurrent gastrointestinal symptoms, not explained by structural or bio-chemical abnormalities, such as in inflammatory bowel disease (IBD) or by an auto-immune disease, such as coeliac disease.

The American College of Gastroenterology defines IBS as ‘abdominal pain or discomfort that occurs in association with altered bowel habits over a period of at least 3months’.

In general, three subtypes of IBS are recognised:

1. IBS with (predominant) constipation;

2. IBS with (predominant) diarrhoea; and

3. IBS with mixed (alternate) constipation and diarrhoea.

Other symptoms include bloating, excess of gas, passage of mucus in the stools, a sensation of incomplete rectal emptying, and fleeting rectal pain.

The symptoms of IBS can be confused with the symptoms of IBD or coeliac disease. It is important to test for this first, before making a definitive diagnosis.

Reasons for IBS could be the poor absorption of a group of short chain carbohydrates, called FODMAPs (Fermentable oligo saccharides, di saccharides, mono saccharides and polyols). These include the following molecules:

  1. Fructose - predominantly found in fruit. Fruits high in fructose include apples, avocados, mangos, peaches and pears. Lower fructose alternatives include blueberries, figs, strawberries and tangerines. A larger list, including vegetables, can be found below.

  2. Fructants - found in wheat

  3. Lactose – found in dairy products

  4. Galactants,- found in some vegetables (onion), as well as legumes, pulses and cabbage. Below is a more detailed list of high FODMAP vegetables.

  5. Polyols - include sweeteners like sorbitol and xylitol, which are a lot sweetener and less harmful for dental health. These are mainly found in sugar-free gums and low-calorie products.

FODMAPS are small and when unabsorbed enter the large intestine, where they can have an osmotic effect, which can alter bowel frequency and consistency. This can lead to wind, bloating, discomfort, nausea and abdominal cramps. Excess gas can slow the movement through the bowel, which leads to constipation.

Unfortunately, there are not yet any reliable tests for FODMAP sensitivity. Particularly home diagnostic tests are not reliable. In fact, the British Dietetic Association has issued a warning against them. Many patients with IBS believe that their symptoms are triggered by specific foods, such as gluten, but this causative relationship is difficult to prove. In fact, when given antispasmodic drugs to alleviate symptoms, 40–70% of patients respond to a placebo alone. Symptoms can have a number of triggers, including both physical and psychological stress, irregular and skipped meals, eating too quickly and insufficient chewing of food.


In general, most patients with IBS can eat a balanced diet without restrictions. It is important to avoid restrictive and monotonous diets without a firm reason to do so. This can lead to inadequate intake of certain nutrients and fibre (which can lead to increased constipation). Rather than self-diagnosing and immediately excluding certain food groups, we should look at our dietary habits as a whole, starting with the way we eat our food. Symptoms are often alleviated if meals are taken in a relaxed environment, with no distractions where the food can be chewed adequately and time is taken to eat. In some patients, in whom symptoms are repeatedly triggered by eating, an exclusion diet may be of benefit. However, it is strongly advised that this is done under supervision of a qualified nutritionist or dietician.

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