Functional Gastrointestinal Disorders

Functional Dyspepsia / Irritable Bowel Syndrome / Functional Bloating / Functional Diarrhea / Functional Constipation

Functional Gastrointestinal Disorders


Functional gastrointestinal (GI) disorders are constellations of upper and / or lower abdominal symptoms unexplained despite adequate medical examination.

The commonest forms of functional GI disorders are functional dyspepsia (FD), irritable bowel syndrome (IBS), functional bloating, functional diarrhea and functional constipation.

These syndromes are the focus of much exciting research and diverse etiological hypotheses are emerging. The most common theories are based on changes in sensation and in brain processing of pain (hypersensitivity), intestinal motility (muscle movement), intestinal permeability, enzyme or neurotransmitter function, the gut flora (microbiome) or chronic inflammation. Some of these changes can occur after an infectious illness or protracted and severe stress. A full discussion of functional GI disorders is beyond the scope of this website dealing with food reactions, but aspects relating to food reactions are elaborated.

Frequency in population

Functional GI disorders affect between 10 to 15% of most populations and a change-over between the different disorders over time is common. There appear to be no major racial differences in prevalence.

Food intolerances and allergies are observed more frequently in patients diagnosed with functional GI syndromes.

Lactose or fructose intolerance, for example, is observed in between 50% and 70% of IBS, patients, respectively. Other frequently reported food reactions in functional GI syndromes are increased symptoms after fatty, gluten or histamine-containing foods. At present it is unclear if food reactions and functional GI disorders are separate causes of the symptoms, or if they represent overlapping or just overlooked diagnoses.

It has been shown that malabsorption of sugars is equally common in healthy individuals as it is in patients with functional GI disorders. The sugar malabsorption, however, leads to more frequent and more intense symptoms of intolerance in patients with functional GI disorders. Furthermore, it has repeatedly been shown that dietary adaptations based on diagnosed food sugar intolerances can very significantly improve symptoms in IBS patients. 

See for example the FODMAP diet


Bloating, abdominal fullness, cramps and pain, diarrhea or constipation, inability to eat normal sized meals, increased intestinal sounds and gas production, reflux (e.g. acid taste in mouth, heartburn), nausea or vomiting are amongst the symptoms commonly seen in functional disorders.

Symptoms are often related to eating or defecation (going to the toilet).

Testing and diagnosis

There is no specific test for functional GI disorders, but other diseases must be excluded by appropriate tests.

This is especially important in case of serious symptoms (red flags) and in individuals older than 40 years. Because of the frequent association of symptoms with eating, testing for food intolerances and, where indicated, food allergies, using validated methods is recommended and is beneficial in a majority of individuals with functional GI disorders.


At present treatment based on symptom control is usual, as the causes of functional GI disorders re unknown. This may include dietary changes based on food intolerance tests, anti-spasmodics, pain killers, laxatives or anti-diarrheals, anti-depressants amongst others.

Further reading

Wilder-Smith CH et al.

Fructose and lactose intolerance and malabsorption testing: the relationship with symptoms in functional gastrointestinal disorders.

Aliment Pharmacol Ther 2013

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