FODMAP Intolerance

FODMAPs (Fermentable Oligo-, Di- and Mono-saccharides And Polyols) are a group of short-chain sugars that can be poorly absorbed and rapidly fermented in the small intestine. Poor absorption leads to increased gas and fluid in the bowel, which have been identified to contribute to the symptoms of bloating, abdominal pain, wind and altered bowel habits in IBS.

The efficacy of a low-FODMAP diet for IBS symptom management is well known. However simply eliminating suspected FODMAPs from your diet without objective proof is inadvisable as FODMAPs are natural prebiotics that help maintain good intestinal microbiota and general gut health. Likewise, it is inadvisable to eliminate food groups such as milk/dairy (containing lactose) or fruits and vegetables (containing fructose) without clinical justification because of their nutritional importance.

If you are suffering from these common gastrointestinal conditions you or your doctor can consider hydrogen and methane breath testing to assess your absorptive capacity for FODMAPs. Breath test results will assist in providing a more complete clinical picture leading to more effective health outcomes. Professional dietetic advice can also help to maximise food options whilst minimising symptoms.  Seek answers, reduce anxiety, and get solutions to your IBS problems today.

Common FODMAPs

High FODMAP Foods

FODMAP subtype

Major Food Sources


Milk, ice cream, yoghurt, custard, ricotta/cream/cottage cheese


Apple, pear, watermelon, mango, cherry, asparagus, artichoke, honey; foods with high-fructose corn syrup (e.g. soft drinks, pastries, commercial cereals)


(Sorbitol & Mannitol)

Peach, plum, prune, apricot, dried fruit, avocado, apple, pear, mushroom, cauliflower, snow pea; sugar-free mints/gum


Mango, peach, date, sugar beet, sweet pea, most dried fruit; confectionery, soft drinks, biscuits/cookies, commercial cereals, ice cream/sorbets, desserts


Lactose, often described as ‘milk sugar’, is a disaccharide found in mammalian milk and dairy products. The enzyme lactase is required in the stomach to digest lactose for intestinal absorption. Lactase enzyme can be either absent (congenital alactasia) or deficient (hypolactasia). Lactase deficiency increases with age, usually starting from early childhood. Ethnic origin affects the risk of lactase deficiency, with the highest prevalence occurring in those from Asian and African backgrounds. Patients with problems digesting milk may confuse lactose intolerance with allergy to the milk proteins casein and/or beta-lactoglobulin, a much rarer condition.


Fructose, often described as ‘fruit sugar’, is a monosaccharide found naturally in all fruits, most vegetables, honey, and is commonly added to food and drink as a sweetener (as fructose or high-fructose corn syrup). Fructose is thought to be absorbed in the small intestine by facilitated diffusion (through a luminal transporter) and paracellular transport (with glucose). In paediatric patients, there is growing evidence that a significant percentage of children with recurrent abdominal pain of childhood (RAPC) have fructose intolerance.

Fructose shouldn’t be confused with fructans, which are chains of fructose molecules naturally occurring in a variety of vegetables and grains. Humans cannot digest fructans, so they are instead fermented by bacteria in the gut. While this can provide health benefits to some, it may cause gastrointestinal distress in others.

Polyols: Sorbitol & Mannitol

Polyols (also called sugar alcohols) are found naturally in a range of fruits and vegetables. They are also added as a sweetener in commercial foods such as chewing gum, mints, sugar-free and diabetic products. Polyols are slowly absorbed in the small intestine and symptoms will probably depend on the amount of polyols consumed, what else you have eaten with it (including other FODMAPs), and how sensitive your gut is at the time. A breath test will determine your ability to absorb a small load of polyols which will then determine whether dietary restriction is required to improve symptoms.


Sucrose, also known as saccharose or more commonly as table sugar, is a disaccharide found naturally in fruits and vegetables and is often added as a sweetener in processed foods. The enzyme sucrase-isomaltase is required in the stomach to digest sucrose and maltose (the sugar found in grains) for intestinal absorption. Congenital sucrase-isomaltase deficiency is a rare condition and is usually apparent in early childhood after introduction of fruits, juices and grains. Sucrose malabsorption can also develop secondary to gastrointestinal illness such as SIBO. Because many foods contain sucrose, it can be difficult to completely remove it from the diet and oral enzyme supplements (sacrosidase) can assist sucrose absorption. 

NOTE: Hereditary fructose intolerance (HFI).
HFI is a rare genetic condition caused by deficiency of the enzyme aldolase B. Where HFI is suspected individuals should strictly avoid fructose, sucrose and sorbitol, and should NOT undergo hydrogen/methane breath testing for these three sugars.

Food Intolerance vs Food Allergy

If you have a reaction after eating certain foods, it may be either a food intolerance or food allergy. However, the two are different medical conditions. Food reactions in general are common, but food intolerances are far more common than food allergies. It can be easy to confuse food intolerance with food allergy but here are some key differences.



All ages

Mostly children

Common condition

Rare condition

Many foods

Few foods

Delayed symptoms (e.g. cramps, bloating, diarrhoea)

Immediate symptoms (e.g. rashes, hives, watery eyes)



Variable and usually not dangerous reactions

Reproducible and usually dangerous reactions

Diagnosis complicated

Diagnosis straightforward

Small Intestinal Bacterial Overgrowth (SIBO) 

In health, there are relatively few bacteria living in the stomach and small intestine due to several natural defence mechanisms preventing bacterial overgrowth. Some of these are: gastric acid secretion, peristalsis (muscle contractions that move food through the digestive tract), intact ileo-caecal valve (that separates the small intestine and the large intestine), and various intestinal secretions containing antibacterial/bacteriostatic properties.

The cause of SIBO is complex however it is associated with disorders of these defence mechanisms. For example, overgrowth of bacteria may occur in achlorhydria (an absence or deficiency of stomach acid) arising from hypothyroidism, medications (overuse of antacids and proton pump inhibitors), surgery (e.g. for weight loss), Helicobacter pylori infection, or certain autoimmune disorders.

In addition to IBS-like symptoms, patients with SIBO can also experience weight loss, steatorrhoea (fatty stool), and nutritional deficiencies such as vitamin B12 and vitamin D. The mainstay of treatment of SIBO is antibiotics, although some patients will be able to have surgery to correct the underlying cause.

It has recently been suggested that IBS symptoms are due partly to SIBO because IBS patients have altered gut microbiota. There is evidence supporting treating a subset of IBS patients (diarrhoea-predominant-IBS) with antibiotics to treat the underlying SIBO. There is also evidence of a role of SIBO in rosacea, with eradication of SIBO resulting in complete resolution.

IBS patients experience recurrent gut symptoms which can significantly affect their quality of life. Patients who self-diagnose may miss out on medical investigations to uncover more serious causes of their symptoms, such as coeliac disease, inflammatory bowel disease, diverticulitis or polyps.

Patients who seek medical attention may be frustrated with sub-optimal management of their symptoms at best, and misdiagnosis and disregard for their symptoms at worst. Persistent suffering can lead to ongoing anxiety and in some cases will lead to impairment in normal activities (e.g. work and social life), or even exploration of “alternative” methods to alleviate the pain. A diagnosis of FODMAP intolerance and/or SIBO with breath testing can provide supporting information that the problem is real, thereby delivering reassurance to you and confidence to your health professional.

Faecal reducing substances is useful in babies and as a screening test to provide an indication of sugar malabsorption however the test has poor specificity and sensitivity. Blood tolerance test for lactose intolerance is a 2 hour test requiring multiple blood collections however it frequently results in diarrohoea and abdominal pain in affected individuals and may be unsuitable in young children. Biopsy for lactose and sucrose malabsorption is performed during gastroscopy, a medical procedure where a long flexible tube is inserted down the oesopaghagus to examine the stomach. Endoscopy and culture of gut aspirate has been described to investigate SIBO but is very rarely performed due to the invasive nature of the procedure and technical limitations in obtaining and processing the samples.

Hydrogen/methane breath testing is currently considered to be the most cost-effective, non-invasive and reliable test to diagnose FODMAP intolerance and SIBO. It is routintely used by general medical practitioners, specialist clinicians, and allied health professionals in the diagnostic work-up of their patients. Breath testing is the only validated assessment method for fructose, sorbitol and mannitol malasbsorption. There is high clinician and patient acceptance for breath testing and with the availability of convenient mail-order kits testing is now even more accessible

It is important not to ‘self-diagnose’. IBS can be caused by many factors and symptoms of IBS can also be seen in other gastrointestinal diseases and disorders and may require medical rather than dietary management. A medical investigation can exclude other serious gastrointestinal diseases (e.g. inflammatory bowel disease, coeliac disease, bowel cancer) and also some gynaecological conditions.

An evidence-based approach helps to identify trigger foods, tailor individual diets, and improve adherence to diet, all of which have been shown to improve symptom control. Breath tests are highly specific and sensitive diagnostic tools. A diagnosis can confirm or eliminate FODMAP malabsorption and/or SIBO as being the cause, or contributing to, your IBS symptoms.

Studies have consistently shown that a low-FODMAP diet improves symptoms in 75% of IBS patients. A low-FODMAP diet may also be a viable option to reduce IBS-like symptoms in patients with non-active inflammatory bowel disease (IBD), or coeliac disease on a gluten-free diet. The following are risk groups for FODMAP intolerance and SIBO and where hydrogen and methane breath testing is useful:



Medically diagnosed IBS or functional gut disorder

Disorders of protective gut mechanisms, e.g. achlorhydria (gastric acid), pancreatic exocrine insufficiency, immunodeficiency syndromes

Coeliac disease or non-coeliac gluten sensitivity

Anatomical abnormalities of the small bowel, e.g.short bowel syndrome, Crohn’s disease, small intestinal obstruction, diverticula, fistulae, surgical blind loop, previous ileo-caecal resection

IBD (Crohn’s disease and ulcerative colitis)

Motility disorders, e.g. scleroderma, autonomic neuropathy in diabetes

Family history of intolerance

Medically diagnosed IBS or functional gut disorder

Lactose intolerance is more common in Asian, African, Latino, Middle Eastern and Southern European ethnic groups

Leaky gut syndrome

Children diagnosed with recurrent abdominal pain of childhood

Chronic fatigue syndrome

Chronic fatigue syndrome

Chronic pancreatitis or liver cirrhosis

Your test results will be interpreted by one of our pathologists (a specialist medical doctor) and a report is sent to your referrer. Self-referred patients will have their reports sent to them.

To ensure the most reliable results we recommend you complete all tests as soon as practical. We recommend one test every 2-3 days. Tests can be performed on consecutive days if you wish and can be completed in any order. Upon completion of your final test, post all tests back to Gastrolab for immediate analysis.

A self-initiated low-FODMAP diet may be well intentioned but without expert guidance there are some important points that may be missed:

  • A low-FODMAP diet may be unnecessary. If you have other conditions your medical professional will advise whether a low-FODMAP diet is recommended for you.
  • Not all FODMAPs need to be restricted and those that are poorly absorbed can be identified by breath testing.
  • Individuals are likely to over restrict the diet by removing FODMAPs they may absorb efficiently. This may lead to nutritional inadequacy.
  • The low-FODMAP diet is somewhat restrictive and consideration must be given to replacing restricted foods with suitable alternatives, maintaining adequate fibre intake, and the need and suitability of vitamin and mineral supplements.
  • FODMAPs are natural prebiotics – they encourage the growth of good bacteria in the gut – so any unnecessary and protracted over restriction may have unwanted effects.
  • The low FODMAP diet has been shown to produce two consistent effects: a reduction in Bifidobacterium species (good bacteria), and a reduction in butyrate levels (an important nutrient for colonic bacteria and colonic cells).
  • The low-FODMAP diet is a 3-phase plan and current knowledge addresses the elimination phase but the other two phases of the diet – determining sensitivities and personalisation – have not yet been studied in clinical trials.
  • There is no information on the safety of the low-FODMAP diet with extended use and so a strict low-FODMAP diet should not be followed long term. Positive or negative breath tests results can assist in fine tuning the FODMAP approach and avoid unnecessary dietary restrictions. The long-term consequences of both observations are currently unknown.