Non-celiac gluten sensitivity (NCGS) is currently defined as : "a clinical entity induced by the ingestion of gluten leading to intestinal and/or extraintestinal symptoms that improve once the gluten-containing foodstuff is removed from the diet, and celiac disease and wheat allergy have been excluded".^{[ ref. needed ]}

It was first described in 1976. Some studies estimate it to be the most common form of the gluten-related disorders - with incidence rates of up to 13% of the (Western) population.

The cause is unknown - though there is speculation that it's an immune-system malfunction of some kind. Some research groups maintain that there is not enough evidence to class NCGS as a distinct clinical disorder.

Currently there is an absence of any reliable biomarkers, therefore, NCGS remains a diagnosis of exclusion."

See : Systematic review: noncoeliac gluten sensitivity Alimentary Pharmacology & Therapeutics, Volume 41, Issue 9 p. 807-820

Note : Recent research is suggesting that a significant proportion ^{[ how much? ]} of those diagnosed with NCGS and IBS are in fact suffering from an intolerance to Fructan - a polymerised version of the sugar Fructose - which is found in all of the wheat family and many other foods. Fructan intolerance can be substantially relieved by adding a powdered enzyme to food. Fructan intolerance (FI) also remains unexplained.

Example ref. Diagnosis and Management of Gluten-Associated Disorders ^{[ paywalled ]}

Also see : Irritable bowel syndrome (IBS)plugin-autotooltip__plain plugin-autotooltip_bigIrritable bowel syndrome (IBS)

"The most common condition seen in gastrointestinal outpatient clinics is irritable bowel syndrome (IBS), which has a prevalence rate of 14-24% in women and 5-19% in men. [...] There is no known structural or anatomical explanation that accounts for the pathophysiology, and the exact cause remains unknown"