What a gluten-free diet is REALLY doing to your health: It’s branded a miracle cure for gut problems, but here’s how it may be making you put ON weight… and what it actually means for your risk of cancer

It was once a niche dietary range designed for people with coeliac disease, but now supermarkets have entire sections dedicated to gluten-free foods.

The market for these products is worth £189million a year in the UK.

That’s striking, given that only an estimated 689,000 people in Britain have coeliac disease – a lifelong autoimmune disorder where eating gluten (a protein found in wheat, rye and barley) causes inflammation in the small intestine.

Yet an estimated 10 to 15 per cent of people follow a low or gluten-free diet.

Doctors suspect many are wasting their money – gluten-free groceries add 35 per cent to the cost of any shop. And they may even be putting their health at risk as a result of nutritional deficiencies, or even weight gain (more on this later).

Furthermore, while those following such diets might think gluten is the problem, the latest research suggests that other components of wheat may play a role, so going gluten-free won’t necessarily help.

Even just thinking that gluten can cause gut symptoms could trigger reactions in some people.

‘It’s likely there are a range of reasons why people follow a gluten-free diet – but some cases will be due to misinformation and misconceptions,’ says Michael FitzPatrick, a consultant gastroenterologist at Oxford University Hospital.

Gluten is the name for a group of proteins – mainly gliadin and glutenin – that give food structure and elasticity.

‘For people with coeliac disease, even tiny amounts of gluten can be toxic,’ says Dr FitzPatrick.

He adds that the average person in the UK probably eats 10g to 15g of gluten a day (equivalent to what is found in three to five slices of bread), whereas for someone with coeliac disease, 10mg to 50mg is the limit – roughly the amount found in 1/100th of a slice of bread.

In coeliac disease, the immune system mistakenly views gluten as a threat and responds by releasing inflammatory chemicals that, in turn, damage the lining of the small intestine and impair nutrient absorption.

Symptoms typically come on within two to six hours and can include vomiting, diarrhoea, abdominal pain and bloating, says Dr FitzPatrick.

‘The inflammation can also affect other parts of the body, causing mouth ulcers, joint pain, headaches and reduced fertility.’

Untreated, coeliac disease can lead to complications such as osteoporosis and, more rarely, bowel cancer. It is diagnosed with blood tests – and sometimes a biopsy of the small intestine.

However, as many as 82 per cent of people who have adopted a gluten-free diet have not been diagnosed with coeliac disease, according to market research from 2022-23.

Dr Patrick Dubois, a consultant gastroenterologist at King’s College Hospital in South-West London, believes that many do genuinely experience symptoms – but have self-diagnosed.

For instance, 13 per cent of people in a UK study self-reported gluten sensitivity, according to The European Journal of Gastroenterology & Hepatology in 2014.

Known as non-coeliac gluten sensitivity (NCGS), this causes similar symptoms to coeliac disease, but does not involve the same immune response. The problem is that there is no clear way to diagnose it.

Dr Dubois says: ‘I see patients who have diagnosed themselves as gluten intolerant using unreliable home tests, but there is no definitive test for it.’

Home tests claim to detect antibodies (released as part of the immune response to wheat or gluten) but these can occur as a normal response to eating a food and do not indicate intolerance, he says, adding: ‘Gluten intolerance is only diagnosed in clinics once coeliac disease has been ruled out.’ And it may also be that gluten is not the cause of gut symptoms at all.

Dr Dubois says: ‘While cutting out wheat may help, it’s often the fructans – not the gluten – causing symptoms such as gas, bloating and pain.’

Fructans are part of a group of poorly absorbed sugars known as Fodmaps (fermentable, oligosaccharides, disaccharides, monosaccharides and polyols) which can trigger symptoms in people with sensitive digestive systems. These sugars are found in breads and cereals and in a number of fruit and vegetables.

In a 2018 study, people who believed they had gluten sensitivity were put on diets containing gluten, fructans or neither (in other words a placebo).

Results showed gut symptoms such as bloating were worse in those eating fructans – while gluten caused no more symptoms than the placebo, reported the journal Gastroenterology. Other components of wheat may also play a role.

‘Proteins called amylase trypsin inhibitors are present in the seeds of all cereals,’ says Dr FitzPatrick of wheat, barley, rye, maize and the naturally gluten-free millet and rice. ‘And they may trigger immune responses and gut inflammation. There’s a lot of research into this right now.’

Some studies even suggest that people simply believe gluten causes gut symptoms – and that’s why they experience them.

In a 2025 study in The Lancet, Gastroenterology and Hepatology, people with IBS who believed they benefited from a gluten-free diet were unknowingly given bars containing gluten, wheat or neither. Symptoms were similar across all groups, suggesting beliefs – not gluten – were responsible in many cases.

A gluten-free diet is also sometimes adopted by people with rheumatoid arthritis (RA) in the hope of reducing inflammation. Elena Nikiphorou, a rheumatologist at King’s College Hospital says: ‘Coeliac disease and RA are both autoimmune disorders, but with RA the immune system attacks the lining of joints – causing pain, swelling, stiffness and sometimes joint damage.

‘But there is no robust evidence that avoiding gluten improves RA outcomes if there’s no coeliac disease or NCGS.’

Meanwhile, there are those who choose gluten-free diets for general health – a reason cited by 38 per cent of gluten-free food consumers in one survey.

Celebrities have helped popularise this trend – including tennis legend Novak Djokovic, who has credited a gluten-free diet with improving his performance.

But as with RA, there is no evidence for the idea that gluten causes widespread inflammation in those without a diagnosed gluten intolerance or allergy.

As Dr FitzPatrick explains: ‘The belief that it is comes from exaggerated claims on social media.’

And of course a ‘gluten-free diet’ could mean any number of things – a healthy diet full of alternative grains such as quinoa, veg and protein – or a diet high in highly processed foods with gluten-free products swapped in.

The latter contain more sugar and fat than standard options in order to improve taste and texture – which can contribute to weight gain, says Dr Dubois.

‘Gluten-free alternatives are highly processed and may lack nutrients,’ he adds. ‘Gluten-free flours are often not fortified with vitamins and iron.’

And there is risk of a lack of fibre, with wholegrains such as wheat a major source.

‘Fibre regulates blood sugar, supports gut health and reduces the risk of conditions such as type 2 diabetes,’ says Dr Dubois.

‘It also promotes a healthy gut microbiome – the collection of good bacteria in the gut – which regulates metabolism and has broader health implications, even reducing bowel cancer risk.’

Low fibre intake is also linked to heart disease, says Dr FitzPatrick, adding of products such as beta-glucan in oats: ‘Some types of fibre bind to cholesterol particles in the digestive system – which reduces the amount absorbed in the bloodstream.’

And finally, blaming gluten for gut symptoms and ‘treating’ it with a restrictive diet, may delay diagnosis of serious conditions.

‘Any change in bowel habits or blood in the stool should be discussed with a doctor, as these could signal serious conditions such as bowel cancer,’ says Dr FitzPatrick. ‘Whilst a gluten-free diet is essential for some, for everyone else, cutting out entire food groups is something I’d never recommend without a clear medical reason.’