Gluten, coeliac disease and gluten sensitivity: what is the difference?

Gluten is a protein found naturally in wheat, barley and rye. It is in many everyday foods, from bread and pasta to bulgur and freekeh, a traditional wheat food across the Middle East and North Africa.

Three different conditions involve a reaction to gluten or to wheat: coeliac disease, wheat allergy and non-coeliac gluten sensitivity. They are often confused, but they are not the same, and the order in which you do things matters. In particular, the UK's National Health Service (NHS) is clear that you should be tested for coeliac disease before you cut gluten out.

What is gluten, and where is it found?

Gluten is found in any food that contains wheat, barley or rye, the NHS explains. The US National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) adds types of wheat such as durum, semolina and spelt, and barley in the form of malt, malt extract and malt vinegar.

That includes many staples. The NHS lists bulgur, couscous, semolina, durum and spelt among the grain foods to avoid on a gluten-free diet. Freekeh, a 2024 study in the journal Toxins explains, is made from immature green wheat grains and is popular across the Middle East and North Africa, so it contains gluten too.

The table draws on the NHS, NIDDK and the charity Coeliac UK. Gluten-free versions of foods such as bread and pasta are widely available. NIDDK also warns that colourings, flavourings, starches and thickeners made from these grains can bring gluten into processed foods, and the NHS notes that some medicines contain gluten too.

Oats do not contain gluten, but they are often contaminated with grains that do. The NHS adds that a small number of people with coeliac disease also react to a protein in pure oats.

How do the three conditions differ?

Coeliac disease is an autoimmune condition: the immune system attacks the body's own tissues when you eat gluten. This damages the small intestine, so the body cannot properly take in nutrients from food. The NHS says it affects at least 1 in every 100 people in the UK, and NIDDK estimates about 1% of people worldwide. Many cases go undiagnosed.

Symptoms range from mild to severe, and mild cases may cause no noticeable symptoms. The NHS lists diarrhoea, stomach aches, bloating and wind, indigestion and constipation, as well as tiredness, unintentional weight loss and an itchy rash. People who keep eating gluten can develop complications such as weak bones (osteoporosis) and iron, vitamin B12 or folate deficiency anaemia. First-degree relatives (parents, brothers, sisters and children) of people with coeliac disease are at higher risk, as are people with type 1 diabetes or autoimmune thyroid disease.

Wheat allergy is a type of food allergy. Coeliac UK describes it as a reaction to proteins in wheat, triggered by the immune system, that usually happens within seconds or minutes of eating. NIDDK notes that some of its symptoms, such as itchy eyes or difficulty breathing, are different from coeliac disease, and that it does not cause long-term damage to the small intestine. Wheat is one of the most common foods to cause allergic reactions, the NHS says, and for some people a reaction can be very serious.

Non-coeliac gluten sensitivity causes symptoms similar to coeliac disease, such as tummy pain and tiredness, but, according to Coeliac UK, no antibodies are produced and there does not appear to be damage to the gut lining. There is no specific test for it. Researchers still debate whether gluten itself is to blame, or other parts of wheat that are removed at the same time, such as FODMAPs. NIDDK also notes that some people with irritable bowel syndrome have more symptoms after eating gluten, even though they do not have coeliac disease.

Why get tested before cutting out gluten?

Because cutting gluten out first can hide coeliac disease. The NHS advises eating foods containing gluten while you are being tested, so that the tests are accurate, and not starting a gluten-free diet until a specialist has confirmed the diagnosis, even if a blood test is positive. NIDDK gives the same advice, and Coeliac UK says it does not recommend trying a gluten-free diet as a first step for this reason.

Testing is recommended, the NHS says, if you have:

• persistent, unexplained gut symptoms such as diarrhoea, stomach ache and bloating;
• tiredness all the time, or weight loss you did not intend;
• severe or persistent mouth ulcers;
• unexplained iron, vitamin B12 or folate deficiency anaemia;
• type 1 diabetes, or autoimmune thyroid disease;
• irritable bowel syndrome (in adults);
• a parent, brother, sister or child with coeliac disease.

Testing starts with a blood test for antibodies. If it is positive, you will be referred to a gastroenterologist, who may confirm the diagnosis with a biopsy, a small sample taken from the small intestine through a thin, flexible tube. If coeliac disease is ruled out, along with other causes, Coeliac UK suggests talking to your healthcare team about non-coeliac gluten sensitivity.

There is another reason to get advice first. NIDDK warns that a gluten-free diet started without guidance may not give you enough fibre, iron and calcium, and that some packaged gluten-free foods are higher in fat and sugar.

What does living gluten-free involve?

If you have coeliac disease, the NHS says you must stop eating all sources of gluten for life, and you will be referred to a dietitian to help you adjust. Symptoms should improve considerably within weeks, although the gut can take years to heal completely: Coeliac UK says between six months and five years, and sometimes longer.

Practical steps from the NHS and NIDDK:

• Read labels every time. Additives such as malt flavouring and modified food starch can contain gluten. In the UK, food labelled gluten-free can contain no more than 20 parts per million of gluten, an amount the NHS says will not cause a problem for most people with coeliac disease.
• Avoid cross-contamination. Store and prepare gluten-free food separately, and do not share utensils.
• Plan ahead when eating out or visiting. Tell the host or the restaurant that you have coeliac disease, ask how food is prepared, and bring food you know is safe if you are unsure.
• Choose oats with care. Talk to your doctor or dietitian first, and only choose oats labelled gluten-free.

Going gluten-free is a treatment for specific conditions, not a general health choice. NIDDK reports that researchers have found no evidence that a gluten-free diet promotes better health or weight loss in the general population, and that a doctor may not recommend it if you do not have coeliac disease or another gluten-related condition. If you do not need to avoid gluten, the NHS lists wholemeal bread and bulgur wheat among good ways to get more fibre.

When to see a doctor

See a GP if you have persistent, unexplained gut symptoms or any of the other signs listed above, and keep eating gluten until you have been tested. The NHS also advises seeing a GP if you think you or your child may have a food allergy.

If you have coeliac disease and your symptoms have not improved, or have got worse, since starting a gluten-free diet, Coeliac UK advises speaking to your GP, dietitian or gastroenterologist.

Call your local emergency number if your lips, mouth, throat or tongue suddenly swell; you are breathing very fast or struggling to breathe; your throat feels tight or you are struggling to swallow; your skin, tongue or lips turn blue, grey or pale; you suddenly become very confused, drowsy or dizzy; or someone faints and cannot be woken. The NHS warns that these can be signs of a serious allergic reaction. If you have an adrenaline auto-injector, use it straight away, then call your emergency number.