The sentence "gluten doesn't agree with me" can describe three different conditions. They work by different mechanisms, are identified by different tests, and require different levels of restriction.
What are the three conditions?
The first is coeliac disease. It is autoimmune and produces measurable damage to the surface of the small intestine.
The second is wheat allergy. It is a classic food allergy; the immune system responds with IgE antibodies.
The third is non-coeliac gluten sensitivity. Symptoms are present, but neither autoimmune damage nor an allergic response can be demonstrated.
All three can produce discomfort after eating wheat. The distinction lies in the mechanism behind that discomfort.
That distinction is practical rather than academic; each requires a different level of care.
How do the mechanisms differ?
In coeliac disease the immune system attacks the body's own tissue. Gliadin is the trigger, but the target is the person's own cells at the intestinal surface.
That attack flattens the villi and creates malabsorption. The damage is visible on biopsy.
In wheat allergy the immune system reads wheat proteins as foreign and produces IgE. The reaction is fast, appearing within minutes.
Symptoms can include itching, hives, lip swelling and shortness of breath. In severe cases there is a risk of anaphylaxis.
In gluten sensitivity neither autoantibodies nor IgE are found. The innate immune system is thought to be involved, but the mechanism is not fully established.
| Feature | Coeliac | Wheat allergy | Gluten sensitivity |
|---|---|---|---|
| Mechanism | Autoimmune | IgE-mediated allergy | Unclear |
| Gut damage | Present | Absent | Absent |
| Test | Antibody + biopsy | Skin/IgE test | Exclusion |
| Reaction speed | Hours to days | Minutes | Hours |
| Restriction | Lifelong, absolute | Wheat | Variable |
Why do the symptoms overlap so much?
Because all three affect the digestive system, and digestive symptoms are not specific.
Bloating, abdominal pain, gas and irregular bowel habits appear in all three.
Fatigue and headache are shared too. Those symptoms are so common that on their own they indicate nothing.
The distinguishing symptoms are rarer: anaemia and loss of bone density in coeliac disease; skin and respiratory signs in wheat allergy.
That overlap makes self-diagnosis impossible. You cannot decide which one it is by looking at symptoms.
Why does the diagnostic order matter so much?
Because when the order is disturbed, coeliac disease can no longer be diagnosed.
The correct order is: exclude coeliac disease first, then wheat allergy, and consider gluten sensitivity last.
Coeliac tests must be done while the person is eating gluten. In someone who has gone gluten-free the antibodies fall and the damage on biopsy begins to heal.
This is why the "let me just try it" approach blocks diagnosis. Testing after a trial requires eating gluten again for weeks; that period is called a gluten challenge and it is difficult.
Gluten sensitivity is a diagnosis of exclusion. Once the other two are ruled out, it is assessed with a controlled gluten challenge.
Is gluten really the culprit?
This is the most interesting part of the gluten sensitivity debate.
Some research indicates the symptoms come not from gluten but from other components of wheat.
The first candidate is fructans, a carbohydrate in the FODMAP group that causes bloating in a sensitive gut.
Wheat is one of the largest sources of fructans in a Western diet. Someone going gluten-free lowers their fructan intake without realising it.
The second candidate is amylase-trypsin inhibitors. These proteins can trigger a response in the innate immune system.
In practice that uncertainty means this: people with suspected gluten sensitivity do not always need a fully gluten-free diet; reducing the amount may be enough.
How is the level of restriction decided?
The three conditions call for three different approaches.
In coeliac disease the restriction is absolute and lifelong. The 20 parts per million threshold applies and cross-contamination matters.
In wheat allergy, wheat is removed entirely, but barley and rye are generally tolerated. That is an important difference from coeliac disease.
In gluten sensitivity the threshold varies by person. Some tolerate small amounts; others do not.
There is therefore no fixed rule in gluten sensitivity. The individual finds their own threshold through controlled trials.
The cost of restriction should be weighed too. Going fully gluten-free unnecessarily is both expensive and lowers fibre intake.
Is there a risk in unnecessary gluten avoidance?
No direct harm, but there are practical consequences.
Fibre intake falls. When wholemeal products are removed, the gluten-free replacements are usually starch-led.
B vitamin and iron intake can drop. Wheat flour is fortified with those nutrients in many countries.
Cost rises. Gluten-free products sell at two to four times the price of their equivalents.
Social restriction is a burden too. Eating out and social occasions become harder.
Most importantly, restriction adopted without a diagnosis can mask a genuine case of coeliac disease.
When should you see a doctor?
When symptoms persist and appear related to food.
Anaemia, unexplained weight loss and reduced bone density are priority reasons to seek assessment.
A family history of coeliac disease raises the risk; its prevalence among first-degree relatives is markedly above that of the general population.
Growth delay and persistent digestive problems in children also warrant assessment.
A critical reminder: do not go gluten-free before that consultation. You have to be eating gluten for the tests to work.
Should businesses know this distinction?
They should, because customer requests call for different levels of rigour.
For a customer with coeliac disease, cross-contamination is critical. Separate equipment, a separate preparation area and informed staff are essential.
For a customer with gluten sensitivity, the ingredients are usually enough. Preparation in the same kitchen often causes no problem.
But the distinction has to be asked. "Is it coeliac disease or a sensitivity?" determines the level of precaution required.
Where there is doubt, apply the highest level of precaution. That is a better approach than refusing service; telling the customer "we can prepare it, but we cannot guarantee against cross-contamination" is an honest and workable answer.
