Quick answer: Gluten is a family of proteins (mainly gliadin and glutenin) found in wheat, barley, and rye. About 1 percent of the UK population has coeliac disease — a serious autoimmune condition where gluten triggers immune damage to the small intestine. A larger group reports symptoms after eating wheat without testing positive for coeliac disease or wheat allergy (“non-coeliac gluten sensitivity”); for some, FODMAPs in wheat (not gluten) are the actual cause. Wheat allergy is different again — an IgE-mediated allergic response to wheat protein. If you suspect any of these, see your GP for proper testing before removing gluten from your diet, because going gluten-free first can mask the diagnosis.
What gluten actually is
Gluten is the catch-all name for a family of storage proteins that occur in the seeds (the grain) of certain cereal plants — most importantly wheat, but also barley and rye. The two largest fractions are gliadin (a prolamin) and glutenin (a glutelin). Together they form the elastic, sticky network that gives wheat dough its stretch and chew, and that gives bread its structure when baked.
Closely related proteins occur in barley (hordein), rye (secalin), and historically in some triticale and spelt varieties. The current FSA / UK regulatory definition of “gluten” for food labelling purposes covers all of these. Oats are botanically distinct and the protein in oats (avenin) is structurally different. Pure oats are usually tolerated by people with coeliac disease, but commercially-grown oats are commonly cross-contaminated with wheat from shared fields and processing equipment — so “gluten-free oats” labelled as such are required to be processed in a controlled supply chain.
Three different conditions, often confused
1. Coeliac disease — autoimmune
Coeliac disease (UK NHS spelling; “celiac” elsewhere) is a serious autoimmune condition affecting around 1 percent of the UK population. The disease mechanism is well-understood:
- The person has a genetic susceptibility (almost always carrying the HLA-DQ2 or HLA-DQ8 immune gene variants).
- When they eat gluten, gliadin peptides cross the intestinal barrier.
- An enzyme (tissue transglutaminase, tTG) modifies the peptides into a form the immune system recognises as foreign.
- The immune system mounts a T-cell response that damages the lining of the small intestine — flattening the villi (the absorptive finger-like projections) and causing chronic inflammation.
- The damage causes nutrient malabsorption (iron, B12, folate, calcium, vitamin D), and a wide range of symptoms — from classic gut symptoms (diarrhoea, bloating, weight loss) to “atypical” symptoms (anaemia, osteoporosis, fatigue, mouth ulcers, infertility, neurological symptoms).
Diagnosis follows NICE NG20 guidance: blood test for tissue transglutaminase IgA antibodies (tTG-IgA) plus total IgA, while still eating gluten daily, followed by referral for endoscopic small-intestinal biopsy if antibodies are positive. The lifelong treatment is strict, complete gluten avoidance — even small amounts of cross-contamination cause continuing intestinal damage.
Coeliac UK estimates that of the 1 percent prevalence, only about a third are currently diagnosed in the UK — the remaining two-thirds are undiagnosed. If you have persistent unexplained gut symptoms, fatigue, anaemia, or a first-degree relative with coeliac disease, see your GP and ask about testing.
2. Wheat allergy — IgE-mediated
Wheat allergy is a classic food allergy: the immune system produces IgE antibodies against wheat proteins, and exposure triggers an allergic response within minutes to two hours. Symptoms range from mild (urticaria, gastrointestinal upset) to severe (anaphylaxis). Wheat is one of the 14 declared major allergens under the UK Food Information Regulations 2014.
Wheat allergy is uncommon (under 0.5 percent of the UK adult population) but more common in children, who often outgrow it. Diagnosis is by IgE blood test or skin-prick testing under allergist supervision. Treatment is wheat avoidance plus an emergency adrenaline auto-injector for those at risk of anaphylaxis. Wheat allergy is part of the wider “cereals containing gluten” allergen category under the UK Food Information Regulations 2014 (which covers wheat, barley, rye, oats, spelt, kamut and their hybrids); wheat-allergic people can usually tolerate barley and rye unless they are also allergic to those.
A specific exercise-induced sub-form (“wheat-dependent exercise-induced anaphylaxis”, WDEIA) is rare but well-recognised — symptoms appear when wheat is eaten and the person exercises within a few hours.
3. Non-coeliac gluten sensitivity (NCGS) — contested but real for some
A larger group reports gut and systemic symptoms (bloating, abdominal pain, fatigue, brain fog, joint pain) after eating wheat, but tests negative for both coeliac disease and wheat allergy. The label “non-coeliac gluten sensitivity” describes this clinically, but the underlying mechanism is contested.
Two competing explanations have evidence:
- Gluten itself may trigger an innate immune response distinct from coeliac disease in a subset of people — researchers have identified raised intestinal permeability and inflammatory markers in some NCGS patients.
- FODMAPs (Fermentable Oligo-, Di-, Monosaccharides And Polyols) — short-chain carbohydrates in wheat (especially fructans) that are poorly absorbed and ferment in the colon — appear to be the actual trigger for many people who self-identify as gluten-sensitive. Blinded trials show that FODMAP reduction can resolve symptoms in some people who got better on a gluten-free diet, even when gluten is reintroduced.
The clinical practical answer: if you suspect NCGS, the right pathway is to see a GP, rule out coeliac disease and wheat allergy formally first (because going gluten-free will mask both diagnoses), and only then trial a controlled exclusion diet — ideally with a registered dietitian, since “gluten-free” diets done badly are nutritionally limited and expensive.
Why coeliac disease occurs in some people and not others
Three things have to coincide:
- Genetic susceptibility. Carrying HLA-DQ2 (about 30 percent of the European population) or HLA-DQ8 (a smaller group) is essentially required. Without these immune genes, coeliac disease is extremely rare. About 95 percent of people with coeliac disease carry HLA-DQ2; most of the remaining 5 percent carry HLA-DQ8.
- Exposure to gluten. Without dietary gluten, no triggering peptides reach the immune system.
- An additional trigger. Many people with the genetic susceptibility eat gluten their whole lives without developing coeliac disease. Something — possibly a gut infection, hormonal change (pregnancy, puberty), or other immune perturbation — appears to flip the switch in those who do develop the disease. The exact trigger isn’t fully understood and is an active area of research.
Coeliac disease is more common in people with other autoimmune conditions (type 1 diabetes, autoimmune thyroid disease, Sjögren’s syndrome) and in first-degree relatives of someone with coeliac disease (about 10 percent risk).
Practical implications for buying supplements and OTC medicines
For the small number of people with coeliac disease, gluten cross-contamination in supplements and medicines is a real risk to watch for. UK and EU rules require declaration of cereals containing gluten as one of the 14 major allergens. Look for:
- “Gluten-free” wording on the label, OR
- Absence of declared allergens including wheat, barley, rye, oats (unless declared gluten-free oats), spelt
- The Crossed Grain Trademark — Coeliac UK’s third-party certification mark
Supplement excipients to watch for in coeliac disease: starch (often maize / corn-based, but check), maltodextrin (usually corn or potato in modern UK supply chains, but sometimes wheat — must be declared if so under FIR 2014), and any “natural flavouring” derived from wheat. The vast majority of UK supplements are gluten-free in practice; explicit certification simplifies the choice.
For OTC medicines, the patient information leaflet declares any wheat-derived excipient. Most UK paracetamol, ibuprofen, antacids, and antihistamines are gluten-free; specific older formulations occasionally use wheat starch, and these are flagged.
Why “going gluten-free without testing” is a poor first move
NICE NG20 is explicit on this: coeliac disease testing requires the person to be eating gluten regularly. NICE specifies more than one meal containing gluten every day for at least six weeks before the antibody test, because the test detects the immune response to gluten. If you go gluten-free first, your antibody levels can drop below the detection threshold, and the test will give a false negative — leaving you in limbo about the actual diagnosis.
This matters because:
- Coeliac disease has long-term consequences (osteoporosis, infertility, certain cancers) that need monitoring.
- Diagnosis qualifies you for prescription gluten-free foods on the NHS in some areas, and for lifelong follow-up.
- Knowing you have coeliac disease is meaningful for first-degree relatives (they’re at higher risk).
- If you don’t have coeliac disease, you may be unnecessarily restricting your diet — gluten-free products are often higher in fat, sugar, and salt to compensate for the missing protein structure, and lower in fibre and B vitamins.
The right order is: see a GP → blood test (while still eating gluten) → biopsy if antibodies positive → then go gluten-free if confirmed.
The bottom line
Gluten is a family of proteins in wheat, barley, and rye. About 1 percent of UK adults have coeliac disease (a serious autoimmune condition); a smaller group has wheat allergy (an IgE-mediated allergic response); and a much larger group reports symptoms with wheat that may be due to gluten itself or to FODMAPs in wheat. If you suspect any of these, get tested while still eating gluten — going gluten-free first masks the diagnosis. For people with confirmed coeliac disease, strict avoidance is the only treatment; for the wider population, gluten-free is a marketing label, not a health benefit by itself.
Related Camden Medicals reading
Sources and further reading
- NICE NG20 — Coeliac disease: recognition, assessment and management
- Coeliac UK — patient information
- Coeliac UK — Crossed Grain Trademark certification scheme
- NHS — Coeliac disease
- NHS — Food allergy (covers wheat allergy)
- FSA — Food allergy and intolerance
Camden Medicals editorial. Information, not medical advice — if you suspect coeliac disease, wheat allergy, or non-coeliac gluten sensitivity, see your GP for proper testing before removing gluten from your diet.