Gluten-free diet: coeliac disease, gluten sensitivity and what to eat

What is the difference between coeliac disease, gluten sensitivity and wheat allergy?

All three are related to wheat, but they work differently. Coeliac disease is an autoimmune disease. In people with a genetic predisposition, the gluten in wheat, barley and rye damages the lining of the small intestine [1]. This damage is detected with blood antibodies and a biopsy, according to the European coeliac disease guideline [1]. Treatment involves completely eliminating gluten for life [1]. See “Coeliac disease in children”.

Wheat allergy is an immune-system reaction mediated by IgE antibodies, the same antibodies involved in other allergies [2]. It can cause anything from an itchy mouth or hives to asthma or a severe reaction, and is diagnosed by an allergy specialist. It requires eliminating wheat [2]. An allergy specialist decides whether other cereals also need to be avoided.

Non-coeliac gluten sensitivity is considered when the other two conditions have been ruled out. Even so, symptoms appear after eating gluten and improve when it is removed. They often include gas, bloating and diarrhoea, and sometimes headaches or tiredness. There is no specific test, so it is diagnosed by exclusion [2]. To see how it fits with other food reactions, our guide to food allergies and intolerances compares them one by one.

Why shouldn’t you eliminate gluten before testing?

Because coeliac disease tests look for the effects gluten leaves in your body. If you stop eating it, those effects fade. That is why blood tests and biopsies are done while you are still eating gluten [1]. If you eliminate it beforehand, the results may be normal even if you have coeliac disease. You are left without a diagnosis and without the follow-up that comes with it.

A genetic test does not settle the question either. Risk genes are common and do not mean that you have the disease [1]. The test is mainly useful for ruling out coeliac disease when those genes are absent.

We often see people in our clinic who have already stopped eating gluten on their own and feel better. That is okay, but tell your doctor. They may ask you to start eating it again for a while before testing; the clinician ordering the tests will guide you [1].

Gluten makes me feel unwell, but I’m not coeliac: what could it be?

This is the question we hear most often in our clinic, and there are several possible answers. Once coeliac disease and wheat allergy have been ruled out, gluten is not always the next suspect. Wheat also contains fructans, sugars that ferment in the gut. In sensitive people, they cause gas and bloating, just like onions, garlic or some pulses.

A trial tested this in people who considered themselves gluten-sensitive. Without knowing what they were given, participants received bars containing gluten, fructans or neither. Fructans caused more symptoms than gluten [3]. And after following a diet low in these sugars, very few people still reacted to gluten itself [2].

Gluten sensitivity exists, but it is worth looking at fructans too before simply eliminating gluten. If your symptoms resemble irritable bowel syndrome, the FODMAP diet explains how these sugars are assessed through a guided, time-limited plan. If milk also makes you feel unwell, read our guide to lactose intolerance.

Which foods contain gluten and which don’t?

Wheat in all its varieties contains gluten, as do barley, rye and spelt. So do products made from them, such as bread, pasta, couscous, semolina, flour, pastries, breadcrumbs, beer and malt. Rice, corn, potatoes, quinoa, buckwheat and unprocessed fresh foods are naturally gluten-free.

Processed foods need more care. Processed meats, sauces, stocks, desserts and battered foods may contain flour or traces. In the European Union, a product can only be labelled ‘gluten-free’ if it contains 20 mg of gluten per kilo or less [4]. ‘Very low gluten’ means no more than 100 mg per kilo [4].

Oats are a special case. The American College of Gastroenterology guideline allows them in the diet of most people with coeliac disease if they are certified gluten-free and tolerated [5]. Regular oats are easily contaminated in the field and at the factory. In addition, a minority of people react to oat’s own protein, so it is sensible to monitor how you tolerate them [5]. If you want to eat oats, discuss it first with your gastroenterologist or registered dietitian.

How to prevent cross-contamination at home and when eating out

Cross-contamination is gluten getting into food without you adding it. It can be crumbs in the toaster, oil used to fry battered food or a spoon that has stirred regular pasta. This matters because when someone with coeliac disease still has symptoms despite following the diet, the first thing to look for is accidental contamination [5].

At home, it helps to have your own toaster, chopping board and colander, cook gluten-free foods first and keep them covered. Do not reuse the water used to cook regular pasta. When eating out, tell the staff when ordering and ask how the dish was prepared, not just what it contains. Chips that are gluten-free on their own are no longer gluten-free if fried in the oil used for calamari.

A gluten-free menu with everyday foods

You can build a gluten-free menu around foods you can eat, with very few speciality products. This example only uses gluten-free pasta. Everything else is vegetables, fruit, pulses, potatoes, corn, rice, fish, seafood, eggs, meat, oil and nuts.

• Monday. Lunch: lamb’s lettuce salad with walnuts and pear, and chickpeas sautéed with onion, paprika and small pieces of turkey. Dinner: creamy mushroom soup, and sea bream with curry-roasted potatoes.
• Wednesday. Lunch: artichokes with gluten-free pasta and pesto, and sea bass baked in parchment with vegetables. Dinner: salad with pomegranate and lemon vinaigrette, and arepas made with gluten-free corn flour and egg.

You can swap the fish for another of the same type. Fruit, nuts or yoghurt make good desserts.

What mistakes do we see most often in our clinic?

Three mistakes come up often, and all three can be addressed.

Trusting ‘wheat-free’ labels. A product without wheat may contain barley, rye or malt. Spelt is a type of wheat, even though it is sometimes sold as an alternative. Look for the words ‘gluten-free’.

Thinking a little won’t matter. In coeliac disease, even small amounts of gluten keep damaging the intestine [1]. That is why we pay close attention to both the kitchen and the plate.

Not getting enough fibre. Removing wholemeal bread and pasta reduces fibre, and packaged gluten-free products often contain less [2]. Make up for it throughout the week with pulses, vegetables, fruit, quinoa and buckwheat.

Does a gluten-free diet help you lose weight?

Not by itself. There is no good-quality evidence that eliminating gluten causes weight loss in people who do not need to avoid it [2]. When someone loses weight after cutting it out, it is usually because they eat less bread, pasta, pastries and processed food.

The opposite can happen too. Packaged gluten-free products tend to contain more fat and salt, and fewer B vitamins and less iron than their equivalents [2]. They also cost considerably more [2]. Some people with coeliac disease gain weight after starting the diet, partly because their gut starts absorbing nutrients properly again [2].

If your goal is weight loss and you have no diagnosis, the usual advice can help. At lunch and dinner, fill half your plate with vegetables, a quarter with protein and a quarter with carbohydrates. Eat fewer packaged foods, whether they contain gluten or not.