Irritable bowel syndrome (IBS) is a functional bowel disorder thought to affect between seven and 15 per cent of the population worldwide, with women being more frequently affected than men. Despite being relatively common, it often goes undiagnosed and this can lead to reduced quality of life for the individual.

Its cause is unknown but possible hypotheses include increased sensitivity of the nerves that line the intestines, altered gastrointestinal motility, alterations in the gut microbiota and low-grade inflammation.

The main symptoms of IBS are diarrhoea or constipation or both, abdominal pain, bloating and abdominal distention and excessive passage of wind.

Diagnosis

There is no test to diagnose IBS, with symptoms playing a main role in diagnosis. According to the Rome IV criteria, IBS can be diagnosed if the individual reports recurrent abdominal pain on average at least one day per week in the previous three months, associated with two or more of the following:

• related to passing stools;

• associated with a change in the frequency of stool;

• associated with a change in consistency of stool;

• symptoms must have started at least six months before.

It is crucial that before IBS is diagnosed, other organic diseases such as inflammatory bowel disease, endometriosis and coeliac disease are ruled out. Red flags that are not typical of IBS and warrant further investigations include unexplained weight loss, rectal bleeding, recurrent vomiting and nocturnal bowel motions.

Therapeutic options

Therapeutic strategies to be used in IBS can and should be different in different individuals, with treatment choice typically being guided by predominant symptoms. Treatment types include pharmacotherapy (e.g. antidiarrheals, antispasmodics, or laxatives), dietary therapy (such as the low-FODMAP diet), exercise, supplements (such as probiotics) and psychological therapies (such as stress management and gut-directed hypnotherapy).

The Low-FODMAP diet

Among dietary therapies for IBS, the low-FODMAP diet (created by researchers at Monash University Australia) has emerged as the most promising option, with studies typically reporting that approximately 75 per cent of IBS patients experience significant improvement on this diet. 

‘FODMAP’ is an acronym which stands for Fermentable Oligo- Di- Mono-saccharides And Polyols. FODMAPs are a group of short-chain carbohydrates that tend to be poorly absorbed in the small intestine, dragging water into the intestine via osmosis.

When they reach the large intestine, they are rapidly fermented by bacteria, generating gasses. Both these actions lead to an increase in the volume of intestinal contents, stretching the intestine walls and stimulating the nerves in the gut. This leads to the sensation of pain in IBS sufferers, who are thought to (i) be more likely to malabsorb FODMAPs and (ii) have an enhanced gut sensitivity.

In addition, stretching of the intestines and excessive fermentation can also cause distention, diarrhoea or constipation.

There are six main classes of FODMAPs:

• Lactose, found in dairy products such as milk, yoghurt and ice cream;

• Fructans, found in fruits such as grapefruit, vegetables such as onions and garlic, and cereals such as wheat and barley;

• Galacto-oligosaccharides, found mainly in pulses, cashews and pistachios;

• Sorbitol, found in fruits such as apples and in sugar-free chewing gum;

• Mannitol, found in vegetables such as mushrooms and cauliflower; and

• Fructose in excess of glucose, found in fruits such as pears, vegetables such as asparagus and in honey.

Implementing the low-FODMAP diet

The low-FODMAP diet is a relatively complicated exclusion diet that should be followed only under the strict guidance of an experienced dietitian.

It is implemented in three stages:

In the first stage, all foods high in all FODMAPs are excluded. This stage lasts about two to six weeks and the aim is to achieve symptom relief.

In the second stage, the different classes of FODMAPs are reintroduced (‘challenged’) in specific ways (that will differ according to each person), with the aim of finding out which FODMAPs the person tolerates and at what doses. This stage lasts about two months.

In the third stage, the information obtained in stage 2 is used by the dietitian to build a personalised diet for the individual, with the aim of liberalising restrictions and expanding the diet while maintaining symptom control in the long term.

Examples of low-FODMAP diet swaps:

• instead of apples, peaches and

watermelon, choose oranges, kiwi and melon;

• instead of garlic, onions, and cauliflower, go for zucchini, potato and carrot;

• instead of wheat bread and couscous, choose gluten-free bread and quinoa;

• instead of cashews and pistachios, choose peanuts and pine nuts;

• instead of normal cow’s milk, choose lactose-free milk.

Manuel Attard is a FODMAP-trained (Monash University) registered dietitian.

www.manuelattard.com