It has been linked to irritable bowel syndrome and those on gluten-free diets say they have lost weight. But is it really the cause of digestive problems - and aren't wholegrains good for us?
It's hard to distil the gluten-free debate so we could just go with Miley Cyrus's take on it. Her gluten-free diet helped her lose weight but, she tweeted: "It's not about weight it's about health. Gluten is crapppp anyway!" It's a widespread view, with 30% of people wanting to cut back on gluten - a protein found in wheats and other grains.
About 1% of the population has coeliac disease, a serious genetically linked autoimmune disease in which the small bowel is inflamed and made leaky by gluten, causing diarrhoea, weight loss, anaemia, osteoporosis and a small increased risk of bowel cancer. It is underdiagnosed (you need blood tests that detect antibodies and a biopsy of the small bowel), with only 20% of affected people being treated. But since 2012 gastroenterologists have also identified a syndrome of non-coeliac gluten sensitivity (NCGS), with symptoms similar to irritable bowel syndrome (IBS), including bloatedness and diarrhoea but also fatigue, "foggy brain" and pain and numbness in the arms and legs. This syndrome should show an improvement in symptoms when following a gluten-free diet.
So if going wheat-free helps you lose weight and makes you healthier, shouldn't we all head for the gluten-free shelves?
The answer is emphatically no. If you have bowel symptoms that you think are gluten-related, you should get checked for coeliac disease. But wholegrains have B vitamins, iron and fibre and in a balanced diet may reduce the risk of diabetes and heart disease. The research on NCGS is inconclusive and the most recent studies show that carbohydrates called Fodmaps, rather than gluten, may be the cause of symptoms. Fodmaps are fermentable oligo-, di- and mono-saccharides, and polyols - and one of them, fructan, is increasingly implicated in irritating the gut, causing flatulence, diarrhoea and bloatedness. Wheat has Fodmaps but so do other foods such as garlic, artichokes, yoghurt and fruit. While Fodmaps are fine for most people, those with IBS don't absorb them so well - one study shows a low-Fodmap diet reduces symptoms in 70% of people.
Recent well designed research (a double-blind randomised controlled trial) from Jessica Biesiekierski's research team in Belgium took 37 people with NCGS - defined as IBS that gets better on a gluten-free diet - and found that symptoms only improved on a low Fodmap diet. The paper, published in Gastroenterology, was accompanied by an editorial suggesting that NCGS may not be a "thing" at all and that Fodmaps, not gluten, may cause symptoms. Biesiekierski warns that you should see a doctor before any exclusion diet and that reducing Fodmaps should be restricted to four to six weeks, and then gradually reintroduced - as they are no more "crapppp" than gluten.
Gluten - good or bad? Photograph: Alamy