We all eat them. Most of us have never heard of them. Some of us could be made ill by them. Alex Gazzola explains what FODMAPs are – and why they’re causing such a huge buzz in the world of gut health and especially in irritable bowel syndrome (IBS).

In an ideal world, problems related to food sensitivity would be easy to explain – and easy to understand. Unfortunately, we don’t live in that world, and it is impossible to talk about FODMAPs without to some extent touching upon the chemistry of carbohydrates – and its terminology.

The word FODMAP is an acronym. It stands for ‘Fermentable Oligosaccharides, Disaccharides, Monosaccharides And Polyols’.

Oligosaccharides, disaccharides, monosaccharides and polyols are four complex words for four groups of simple sugars, or simple carbohydrates, all of which occur naturally in all plant and dairy foods to varying degrees.

Why can FODMAPs be a problem?

In general, these sugars are poorly absorbed and poorly digested in the small intestine. As they pass through the small intestine, they draw water into the bowel, and then as they pass further into the large intestine, they are fermented by the healthy bacteria which live there, leading to gas production. These are perfectly normal processes in all of us.

However, some individuals’ digestive systems are better equipped at handling them than others. Problems can arise in individuals with low levels of key digestive enzymes or whose guts are particularly ineffective at absorbing these sugars. If too great a level of FODMAPs reaches the large intestine, a lot of water can be drawn in and lot of gas may be produced, leading to sometimes severe symptoms of bloating, wind and diarrhoea. Some of these symptoms can be amplified in those with especially sensitive bowels, or other gut problems.

In which foods are FODMAPs found?


Let’s take the ‘M’ of FODMAP first.

‘Mono’ means ‘one’ and ‘saccharides’ means ‘sugar’ – so the term monosaccharides refers to the simplest of sugars, composed of just one molecular sugar ‘unit’.

Examples of monosaccharides are glucose and fructose. Glucose is very easily absorbed by the body, and so does not cause a problem and is not considered a FODMAP. But fructose – a sugar found in ‘free’ form in many fruits – can cause a problem as it is poorly absorbed.

The main sources in the diet are honey, high-fructose corn syrup (often added to sweet or sugary foods and soft drinks as a cheap sweetener), and certain fruit and fruit juices – apples, grapes, mango, watermelons, pears and cherries.


‘Di’ means two, so the disaccharide sugars are made up of two sugar units.

The key example in the diet is lactose – the sugar found in milk and milk products, not only milk from cows, but goats, sheeps and other animal milks too. Lactose intolerance is well documented and this is the key FODMAP intolerance that most people have heard of and are familiar with. Around 5% of the population may be affected by it to the extent that they need to moderate their intake of several dairy foods. It is caused by a deficiency in the enzyme lactase, which breaks down lactose into its constituent sugar units.

The worst culprits tend to be milk, cream, custard and soft cheeses. Probiotic yoghurt and hard or mature cheeses are generally well tolerated, as the lactose in these foods breaks down during the production or maturation of these dairy products.

There are low-lactose milks now available too, and low-lactose brands such as Lactofree have several products in their ranges.


‘Oligo’ means ‘a few’ so oligosaccharides have several sugar units and are slightly more complex types of sugars than monosaccharides or disaccharides.

Different types of oligosaccharides are found in various foods.

Fructo-oligosaccharides (FOS) and a similar class of carbohydrates called inulins are found in wheat starch, onion, garlic, artichokes (globe, and especially Jerusalem), asparagus, bananas, beetroot and chicory.

Galacto-oligosaccharides (GOS) are found in hummus, some nuts (cashews, pistachios), but mainly in beans and pulses – and are responsible for their ‘windy’ reputation!

Humans do not have the enzymes to digest these more complex sugars, so they can be particularly problematic in some people.


The final letter in the FODMAP acronym is P for Polyols. Polyols are sometimes called sugar alcohols, although they are not alcoholic in the usual sense.

They include sorbitol, maltitol, mannitol, xylitol and isomalt. These are very poorly absorbed. They are used as sweeteners, and tend to be found in slimming drinks and diet foods, chewing gum, low-sugar soft drinks and diabetic foods.

But they are naturally found in mushrooms, and some fruits and their juices, too: for instance, apples, pears, avocado and stone fruit (e.g. plums, apricot, cherries etc), and in berries.

Diagnosis – sometimes easy, sometimes not …

Diagnosing fructose or lactose intolerance is typically via a hydrogen breath test (HBT), usually available through your GP who can refer you for one.

The HBT involves drinking a sugar solution on an empty stomach, and subsequently monitoring your exhaled breath for increased levels of hydrogen for several hours. Hydrogen gas is produced in the body by the bacteria which live in our gut when they ferment carbohydrates. Some of this hydrogen passes into the blood vessels and is passed out through the lungs. So a rise in hydrogen levels in your breath can signify an intolerance to either fructose or lactose.

However, with regard to the more complex FODMAPs, a diagnosis can be trickier. It requires a FODMAP-trained dietitian and an elimination diet.

In an elimination diet, the patient has to undertake a very low FODMAP diet for up to two months, until symptoms subside. (If symptoms do not disappear, then the problem is not FODMAP related, and may not even be food related.) Then, under the care of the trained dietitian, foods and drinks containing FODMAPs are reintroduced individually and gradually, in an attempt to identify culprits by monitoring any symptoms and reactions which return.

What if you have a FODMAP problem?

If your dietitian and/or your doctor find you have a FODMAP problem, it doesn’t mean necessarily that you will have to avoid all high FODMAP foods.

First, it is unlikely you will react to foods in all four groups. Second, even if you do react to many sugars and many foods, moderating or reducing your intake of those foods may be all you need to do, in order to establish a safe ‘tolerance’ level where you can enjoy modest portions of the foods without experiencing troublesome symptoms.

It may be the case that you merely need to make some changes to the way you eat, or alter some particular habits that you’ve picked up. Drinking lots of fruit juice on an empty stomach first thing in the morning could lead to a problem, for example, as might a habit of consuming lots of chewing gum throughout the day (sugar-free gum may have polyol sweeteners added to it). Small changes can have big beneficial effects, sometimes.

Your dietitian may also advise you, for example, to reduce wheat, onions and garlic, which can be highly problematic to many people. Wheat is not especially high in FODMAPs, but we tend to eat so much of it (in cereals, pasta, bread and other baked goods), that the FODMAP quotient from wheat does add up considerably in some of us. Processed foods such as ready meals and ready-made sauces in the UK are usually rich in onion and garlic and high in FODMAPs, so these must often be avoided under the plan.

A low-FODMAP or reduced-FODMAP plan will be devised and tailored for you by your dietitian, to accommodate your own food tastes and preferences, as well as any other dietary restriction that you may have, such as vegetarian or vegan.

Who can the low-FODMAP diet help?

The low FODMAP diet was devised by an Australian team of Professor Peter Gibson and dietitian Dr Sue Shepherd as a therapeutic diet for those with irritable bowel syndrome (IBS) and other functional gut disorders.

The diet works by drastically reducing gas production and fluid in the bowel, and in a number of studies has been shown to be effective in between two-thirds and three-quarters of IBS patients who adhere strictly to it – although it is important to stress that these studies were all conducted with patients being supported by trained dietitians.

However, the diet may have more far-reaching potential than solely as an IBS therapy in future. It may help some patients with coeliac disease who have ongoing symptoms (which they often attribute to accidental gluten intake). It may also be useful in reducing the output in patients with stomas who use colostomy bags, and also to relieve gut symptoms in patients in remission from inflammatory bowel disorders such as ulcerative colitis and Crohn’s disease.

It also may prove to be a possible solution to some of those who are diagnosed with non-coeliac gluten sensitivity (NCGS), a condition where coeliac disease and wheat allergy have both been ruled out, and yet a patient seems to experience symptoms when consuming gluten.

NCGS is a condition about which there remains some unanswered questions. It is not clear whether the immune system is involved, and some experts believe it may not be due to gluten at all, and that the name is therefore inappropriate. It is possible that some who react to gluten-containing foods are actually reacting to the FODMAPs in wheat starch, and mistaking this for a gluten-related reaction.

Anecdotally, many people who feel they are intolerant to wheat feel they can tolerate spelt – a different type of wheat, which naturally also contains gluten. Curiously, bread made from spelt wheat is lower in FODMAPs than bread made from ordinary wheat, and this may account for those patients who feel they can consume it without problem. Accordingly, spelt bread, rather than wheat-free or gluten-free bread, may be a good alternative to those for whom gluten-related disorders and wheat allergies have been ruled out. Strangely, this is not mirrored with spelt wheat pasta, which appears to be just as FODMAP-rich as durum wheat pasta. Researchers do not know why this might be – but this is not unusual in the science of FODMAPs, as there is still an awful lot for researchers to learn about them.

Are there any downsides to the low-FODMAP plan?

Making minor adjustments to your diet is unlikely to have any real detrimental or nutritional effects, provided any obvious deficiencies are countered.

There are, though, a few down sides to a stricter low-FODMAP diet. Generally, calcium intake is lowered considerably, and it seems that the diet reduces colonies of healthy gut bacteria in the bowel too. It is not known whether this is a long-term effect, or whether the so called ‘microbiome’ in the gut normalises in the long run, and more studies are needed.

Obviously, it is very restrictive and complicated, so willpower is required on behalf of the patient, who needs to maintain a close working relationship with his or her dietitian and take care with reading and checking labels, and of course with eating out.

Some low-FODMAP GF foods

As a relatively new field of research, the FODMAP content of foods is still being researched, and may vary according to its breed, the climate or soil in which it is grown, its preparation, its ripeness and various other factors.

There is differing data on some foods – such as bananas – and dietitians will have access to up-to-date data and figures – another reason to avoid ‘going it alone’ when it comes to FODMAPs, as some of the information online may be out of date or inaccurate.

Here is a selection:

Vegetables: some green vegetables (kale, green beans), salad vegetables (lettuce, tomatoes and cucumber), most root vegetables (carrot, potato, turnip and parsnip), Mediterranean vegetables (courgette, peppers, aubergine and fennel) and the ‘squash’ vegetables (pumpkin, butternut and others).

Fruit: citrus fruit, strawberries

Protein sources: meats and seafood

Grains: rice, gluten free oats, millet, buckwheat, amaranth, quinoa, corn and most products made from them or their flours, such as bakery and pastas.

Mature cheeses, butter, eggs.

Dark chocolate

How to find a FODMAP-trained dietitian

Your doctor may be able to refer you, but he or she may not be familiar with work in this area as it is relatively new. Instead, you can search for a dietitian online at www.freelancedietitians.org or email King’s College London (the key centre in the UK for work in FODMAPs) at fodmaps@kcl.org.uk and they can send you a list of approved dietitians.


Monash University: www.med.monash.edu/cecs/gastro/fodmap

This is the centre in Australia which has developed the low-FODMAP plan for IBS.

Sue Shepherd’s site: http://shepherdworks.com.au

Co-developer of the low FODMAP plan

King’s College London FODMAP pages: www.kcl.ac.uk/fodmaps

Dietitian Julie Thompson’s website and blog: www.calmgutclinic.co.uk and http://clinicalalimentary.wordpress.com  She is a specialist gut health dietitian, and the IBS Network’s dietitian too.


This article first appeared in Allergy Newsletter No.112, Winter 2014.

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