Irritable bowel syndrome (IBS) is a common condition of the gastrointestinal tract, and many people say that food either triggers or exacerbate their IBS symptoms. Yet, there is considerable evidence that making a change to a diet low in FODMAPs can help to reduce these symptoms.

IBS is a functional condition, meaning that there are no structural changes to the gut, but that does not mean that the symptoms are not real. The main symptoms of IBS are abdominal pain, bloating and a feeling of distension, with an altered bowel habit that is not explained by other causes. This might entail abnormal stool frequency, stool form, or passage of the stool through the gut.

If you suspect you have IBS it is important to be checked out by a doctor. This is because there are other conditions that may have similar symptoms and these should be ruled out before a diagnosis of IBS can be given.

There are several theories as to what causes IBS symptoms. In fact, it seems likely that there could be several factors that together lead to its development.

The gut-brain axis and IBS

We know that stressful or traumatic events can make IBS symptoms worse. Researchers think that in people with IBS there may be changes in how the gut and the brain communicate. This powerful gut-brain connection may lead to alterations in the spontaneous muscular contractions of the gut. Or, it could be that some people are hypersensitive to the expansion of the gut during the digestive process.

Another theory suggests that there could be an increased level of activation of the immune system leading to inflammation and pain. This could be associated with changes in the composition of the gut bacteria and/or having a more permeable gut lining, otherwise known as a leaky gut.

Other factors that have been studied include a genetic susceptibility and specific food related triggers such as gluten.

In any case, according to the research, the majority of people with IBS symptoms can reduce these symptoms by following a low FODMAP diet.

What are FODMAPs?

FODMAP is an acronym for Fermentable, Oligosaccharides, Disaccharides, Monosaccharides And Polyols. These are relatively small carbohydrate molecules that humans poorly digest. Each of these types of carbohydrates has been found individually to contribute to IBS symptoms.

Some examples of FODMAPs:

Oligosaccharides

• fructo-oligosaccharides found in many fruits and vegetables such as bananas, onions, garlic and grains such as wheat
• galacto-oligosaccharides found in vegetables especially peas and beans, as well as butternut squash and beetroot

Disaccharides

such as sucrose, lactose and maltose; for example lactose is milk sugar, so it is found in dairy products

Monosaccharides

such as glucose, fructose and galactose; fructose is fruit sugar, so it is found in apples, pears, dried fruits, honey and fruit juice

Polyols

such as sorbitol, mannitol, xylitol and isomalt, found in for example, sweet corn, apples, cauliflower, mushrooms, and artificial sweeteners

As you can see from these examples, an otherwise healthy diet, high in fruits and vegetables, is likely to be high in FODMAPs. The low FODMAP diet minimises all of these carbohydrates collectively. Then when symptoms subside these foods can be added back into the diet, which helps to identify which foods a person can tolerate and which, if any, they cannot.

How does a low FODMAP diet reduce IBS symptoms?

As I mentioned earlier, the FODMAP carbohydrates are poorly digested. This means that they travel through the upper parts of the digestive tract relatively intact. However, in the latter parts of the gut the gut bacteria can rapidly ferment them. This fermentation process produces gasses that may be at least partly responsible for the bloating and feeling of distension.

By limiting the amount of fermentable carbohydrates, we ensure the gut bacteria have less available substrate, and therefore gas production is much lower, which reduces symptoms.

Is the low FODMAP diet a cure for IBS?

The low FODMAP diet is not a cure for IBS, but it does allow individuals to manage their IBS symptoms. In fact, around 70% of people with IBS may gain good symptom control with a low FODMAP diet.

An important point is that a strict low FODMAP diet should not be continued in the longer term. This is because studies show that the population of gut bacteria is likely to be adversely affected.

For more information on the low FODMAP diet you could take a look at the Monash University FODMAP website.

You might also like my page Low FODMAP foods list

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The benefits of probiotics for IBS
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