Bloating, abdominal pain and distension, excess wind and a change in bowel habits are not just a sign that you have been over-indulging. In fact, up to 1 in 5 people displaying these symptoms are diagnosed with a disorder known as irritable bowel syndrome (IBS). The term IBS does not necessarily denote a condition in itself, but rather is used to explain the presence of digestive complaints in the absence of anatomical abnormalities, often investigated via a colonoscopy or endoscopy. Whilst the cause for the disorder is not completely understood, many strategies have been used to try to better manage the condition, with varying levels of success. Following a low FODMAPs diet is one of these strategies; it has received a lot of attention, with studies suggesting up to a 70% success rate in reducing symptom severity. Nutritionist Maxine Sheils explains.

FODMAP is an acronym for fermentable oligosaccharides, disaccharides, monosaccharides and polyols. Whilst it may initially sound highly scientific and rather complicated, these are effectively foods that contain high levels of poorly absorbed, short-chain carbohydrates. As high FODMAP foods are poorly digested and absorbed in the small intestine, once they reach the large intestine they often ferment and produce gases, which may explain abdominal pain and distension, excessive wind and bloating – all symptoms associated with IBS. Some high FODMAP foods may also have an osmosis effect, attracting water into the digestive tract, which may explain diarrhoea symptoms, common in IBS-D.

There are a huge range of foods falling under the category of high FODMAPs; these include, but are not limited to, the following:

The short-chain carbohydrates that make up FODMAPs are digested and absorbed in different ways. Fructose (monosaccharide) is absorbed via 2 different pathways, one of which may be down-regulated, in which case the second pathway can be used as an alternative as long as glucose is also present. Sugar, for example, contains fructose and glucose, so if the first pathway is down-regulated, the second pathway can be utilised. Alternative sweeteners such as honey and agave syrup, however, contain an excess of fructose to glucose and are therefore considered high FODMAP foods, as the fructose cannot benefit from the second pathway for digestion if the first pathways is down-regulated.

Lactose (disaccharide) requires the digestive enzyme lactase to break it down and make it easier for the body to digest. As discussed in a previous article ‘Dairy versus alternatives: what you need to know’, levels of lactase can decrease shortly after the weaning period in some cultures (mainly Asian and African cultures), making lactose intolerance widespread.

Studies indicate that up to 34% of ‘healthy’ people (i.e. those who do not suffer with a digestive disorder) malabsorb fructose, 16% of healthy Caucasians are considered lactose intolerant and up to 60% of healthy individuals malabsorb sorbitol and mannitol (polyols), whilst everyone (whether healthy or those with digestive disorders) poorly absorbs fructans and GOS (oligosaccharides) due to the absence of digestive enzymes to break down these carbohydrates. (1) The high FODMAP phenomenon, therefore, is not restricted to those with IBS.  

The inability to absorb high FODMAP foods is considered not only normal but also beneficial to the health of the gut for several reasons: the osmosis effect of high FODMAP foods supports natural laxation; the fibre content of some high FODMAP foods act as a prebiotic – feeding gut bacteria; fermentation of high FODMAP foods provides a protective effect for health – keeping the cells of the digestive system healthy.

As high FODMAP foods can lead to fermentation and therefore the production of gas (methane and hydrogen), breath tests can be used to monitor the presence of gases in the digestive tract upon intake of a test carbohydrate, such as fructose. If the test carbohydrate is not digested, it is likely to ferment and produce gases, leading to a positive reading. Both IBS sufferers and ‘healthy’ individuals have been shown to produce the same levels of hydrogen gases as a result of taking a test carbohydrate (1); IBS sufferers, however, appear to be more sensitive to the pain associated with abdominal distension, which may be a consequence of methane production as a result of altered gut bacteria and delayed gut motility (possibly resulting in constipation). (1)

Whilst studies have shown up to 70% success rate in alleviating digestive complaints when following a low FODMAP diet, there are many limitations that need to be considered and accounted for before proceeding. (1) Following a low FODMAP diet for a 4-week period has been shown to lower levels of beneficial gut bacteria, as some high FODMAP foods are considered prebiotic and therefore feed the bacteria of the digestive tract. As we continue to learn more about the benefits of the gut bacteria in supporting immune health, digestion and many other bodily processes, it is clear that following a diet that may reduce beneficial bacteria needs to be managed optimally, with use of low FODMAP prebiotic foods and a probiotic supplement.

Many fruits and vegetables that are restricted when following a low FODMAP diet are also rich sources of nutrients, including calcium, iron, zinc, folate B, D vitamins and natural antioxidants; these should not be reduced without thorough planning for suitable alternatives. (2) 

When considering a low FODMAP diet to support the symptoms of IBS, it is important to understand that high FODMAP foods form part of a healthy and balanced diet and, whilst high FODMAP foods may trigger unpleasant symptoms, consumption of high FODMAP foods are not the cause of IBS; there is still no known cause. There are many factors that are considered to play a role, including low-grade inflammation, compromised bacteria, problems with gut motility and visceral hypersensitivity. (3) Therefore, a low FODMAP diet should only be considered as a short-term strategy to help alleviate digestive complaints whilst all other factors are also considered and corrected. 

Following a low FODMAP diet can also be a source of confusion, as sprouting and fermenting (outside the gut, using yeast or bacteria) of some foods can change their FODMAP content. For example, wheat is considered a high FODMAP food but fermenting wheat to produce sourdough is considered a low FODMAP food as the process breaks down the fructan content. Cabbage, however, is considered a low FODMAP food but once fermented in the form of sauerkraut, contains high levels of FODMAPs. Sprouting of wheat, rye and other grains can also reduce their FODMAP content, whereas sprouting chickpeas can slightly increase the FODMAP content. Seeking the support of a qualified nutritionist is recommended.  

1. Barrett, J.S. ‘Extending our knowledge of fermentable, short-chain carbohydrates for managing gastrointestinal symptoms’, Nutrition in Clinical Practice, 28 (3), pp 300-306.
2. Catassi, G., Lionetti, E., Gatti, S., et al. ‘The Low FODMAP Diet: Many Question Marks for a Catchy Acronym’, Nutrients, 9 (3), pp. 292.
3. Altobelli, E., Del Negro, V., Angeletti, P.M., et al. ‘Low-FODMAP Diet Improves Irritable Bowel Syndrome Symptoms: A Meta-Analysis’, Nutrients, 9 (9), pp. 940.