The supermarket aisle has become a confusing place. It used to be full of recognizable items like cheese and butter; now you find yourself bamboozled by all manner of odd alternatives such as ‘raw’ hummus, wheat-free bread and murky juices. You have to stay pretty alert to make sure you pick up a pint of proper milk, rather than a soy-based alternative or one free from lactose. Supermarkets have become shrines to ‘clean eating’, a faith that promises happiness, healthiness and energy. Food is to be worshiped — and feared.

As with all growing religions, you know it by its disciples. On The Great British Bake Off, one contestant, Ugne Bubnaityte, has denounced cake as a ‘nutritional sin’ and she hopes to win with low-fat, vegan and gluten-free recipes. Commercially, she’s on to a winner: the market for gluten-free food is soaring and is forecast to grow by 46 per cent, to £560 million, within two years. For those who can’t wait, there’s always the NHS, which wrote 211,200 prescriptions for low-protein or gluten-free food last year (including cakes and pizza). As Dr James Cave, editor of the Drugs & Therapeutics Bulletin, puts it, the NHS is ‘acting as bakers and grocers’.

The high priestesses of this new religion are a group of young, attractive women who amass hundreds of thousands of followers online as more and more people turn to them for guidance. Essentially recipe bloggers, they are becoming revered for telling us what to eat and what not to eat. In an age of confusion, they seem to offer a path.

There’s 25-year-old Madeleine Shaw, a ‘holistic nutritional health coach’ who believes in ‘enlivening the hottest, happiest and healthiest you’ and offers a ‘chia seed egg substitute’ to use in recipes. Ella Woodward, 23, bounced back from a rare illness after adopting a new plant-based diet and entices her followers with sweet potato brownies. Tess Ward, 23, has written a cookbook called The Naked Diet which replaces the conventional chapter headings — ‘Breakfasts’, ‘Starters’, ‘Mains’, ‘Puddings’ —with ‘Pure’, ‘Raw’, ‘Stripped’, ‘Clean’ and ‘Detox’. And there’s the Hemsley sisters, Jasmine and Melissa, whose bestselling cookbook The Art of Eating Well contains no recipes with grains, gluten or refined sugar.

Woodward recommends raw, rather than pasteurized, coconut water, which is tinted pink ‘because of all those antioxidants’ and warns about the dangers of dairy. Milk, she says, ‘can actually cause calcium loss in our bones! This is because milk causes the pH of our bodies to become acidic which triggers a natural reaction in our bodies to bring the pH of our blood back to neutral’. When we drink milk, she says, calcium is drawn from our bones in order to rebalance the acidity it causes, which can result in a calcium deficit.

This is news to nutritionists. Milk can, if consumed in absurdly excessive quantities, lead to a condition called milk-alkali syndrome — but this is more commonly caused by over-consumption of calcium supplements than by guzzling milk. More common is calcium deficiency, which the NHS says can be caused by cutting out dairy products.

Sian Porter, a consultant dietitian, warns that ‘if people do not plan really carefully for substitutes for food groups then you can end up malnourished yourself.’ So these diets are not simply a silly fad that might leave you a little skinnier. The pursuit of wellness and ‘clean eating’ could, in the long-term, make you unwell. ‘Often, these people have found that an approach works for them, and that’s great,’ says Porter. ‘But it doesn’t mean that it will work for anyone else.’

The Hemsley sisters write on their site that gluten ‘breaks down the microvilli in your small intestine, eventually letting particles of your food leach into your bloodstream, which is referred to as “leaky gut syndrome”’. This can be the case, but only for those suffering from coeliac disease. It is not the case for those who do not have this autoimmune condition. Ian Marber, a nutrition expert who is a coeliac, says that many of the wellness gurus have ‘little understanding of the responsibility that comes with discussing food. Everyone eats, so everyone thinks they are an expert, but these people are injecting an unwelcome degree of paranoia into society, without any scientific backing.’ If you drank too much wine and have a hangover, he says, you blame too much alcohol. ‘But if people eat too much bread, they would rather say they have some sort of intolerance than admit they over-indulged.’

It’s not entirely clear why ‘eating clean’, by avoiding gluten and certain carbohydrates, would keep people healthy. As the British Dietetic Association puts it, carbohydrates are crucial; they represent the body’s main energy supply and should make up half of each meal. They are not inherently fattening; any unneeded energy ‘will be converted into fat no matter what the source’. Those low-carb diets? Research suggests they ‘don’t seem to help people lose weight and keep it off’. But the overwhelming message from the plethora of people urging us to eat cauliflower couscous and gluten-free loaves is a simple one: carbs are bad.

The fear of gluten, milk and other newly unfashionable foods could also damage children whose parents foist their fads on the whole family. ‘Muesli-belt malnutrition’ was first identified by doctors in the late 1990s, when they found children were suffering as a result of the excessively restrictive diets that their health-conscious middle-class parents had developed. Now, with the internet so readily at hand to offer quick diagnoses, the new obsession seems to be with allergies and intolerances, and cutting out all sorts of foods in order to deal with them.

It ties into a similar mantra espoused by those who pursue wellness — that you can heal yourself — and your family — by cutting out entire food groups. Earlier this year, the charity Sense About Science warned that parents were risking leaving their children malnourished by restricting their diets in order to deal with perceived health problems. A decade ago, a study of 969 children in the Isle of Wight found that a third of them were thought by their parents to have food allergies; in fact, only 5 per cent did.

It’s not often that science intrudes into the world of ‘wellness’ fads. To become a clean eating guru, a cheery demeanor seems to matter far more than proper qualifications. Ella Woodward, Madeleine Shaw and Tess Ward all studied History of Art. The latter two then studied an online course with the Institute for Integrative Nutrition. This course, based in America, claims to be a ‘movement’ working to reverse the health crisis by promoting the concept of ‘bio–individuality’ — a concept coined by its founder Joshua Rosenthal (who eats a gluten-free diet). It hinges on the idea that one person’s food is another person’s poison.

The institute claims that the qualification it offers is ‘rooted in science’ — a claim which puzzles Dr Max Pemberton, Spectator Health editor and an eating disorders specialist. ‘The minute you scratch beneath the surface,’ he says, ‘you realize it isn’t.’

It is certainly rooted in commercial logic: the surging demand for wellness gurus means that those brandishing credentials are welcomed by an audience often mistrustful of mainstream medicine. The institute is happy to boast about this on its website, quoting a student who says that ‘with the ability to see clients before graduation, my education was paid for before it was completed’.

Successful gurus are cashing in: the Hemsley sisters sell their own brand of ‘spiraliser’, a gadget for turning courgettes into ‘courgetti’, a gluten-free pasta substitute. Supermarket sales of courgettes are soaring thanks to health-conscious consumers embracing the vegetable, which is presented as having near-miraculous powers.

The avocado, once considered an enemy because of its high fat content, has been forgiven; and in America, where many of these trends originate, sales of the fruit have quadrupled since 2000. It is a good time to grow avocados, a bad time to herd cows.

The pursuit of wellness is a dream, and every dream has a darker side. On a number of pro-anorexia websites, there are discussions about many of the topics favoured by the wellness brigade. On a popular clean eating website, one girl writes that the ‘spring rolls are easy to take to work and look like you’re actually eating proper food, lol’. On a thread devoted to the topic of chia seeds, a user comments that they are ‘really helping with hunger’ because ‘when they get into your stomach they absorb the water and expand, making you feel full’.

While the wellness gurus deliberately avoid any discussion of eating disorders and diets, their attitude to food is often worrying. Madeleine Shaw admits that she ‘wasn’t always this healthy’ and that as a young girl she had ‘quite a torturous relationship with food and my body’. She suffered cycles of ‘depriving and bingeing’, which led to her hair falling out and her periods stopping. At one point, she reportedly ate only rice cakes and fruit. She is careful not to refer explicitly to an eating disorder, but it certainly sounds as if she had a disordered way of eating. Phrases used by devotees of the religion, such as ‘eat clean’ or ‘it’s not a diet, it’s a lifestyle’, feature frequently on pro-anorexia chat rooms. In a blog on the Anorexic Angels website, which has since been taken down, ‘Ima_Be_Thin’ referred to gluten-free as the ‘best diet trick ever’ because ‘it’s just such a common allergy no one 2nd guesses me’. Dr Bijal Chheda-Varma, a consultant at the Nightingale Hospital in London who specialises in eating disorders, says that she is seeing more and more patients who have eschewed certain food groups based on advice they have read online. ‘Clean eating’ is a term she is used to hearing as a way of justifying a particular diet. ‘Apps and social media do not necessarily cause obsessive behaviour, but can increase obsession over food,’ she says.

Social media websites are wary about being associated with eating disorders; Instagram’s privacy and safety centre has a whole section dedicated to the topic. A search for the phrase ‘anorexia’ brings up a warning about ‘graphic content’. But type in ‘orthorexia’ — the term associated with obsessive healthy eating — and no such warning appears. More than 80,000 images pop up, tagged with those increasingly familiar incantations: #wellness #eatclean #nourish.

The sentiment underlying this new cult isn’t a bad one. Most of us would like to be healthier. But we can’t expect the supermarkets to let us know what healthy is — their job is to flog us food, and they do it very well. The overwhelming advice from the people who know a lot about nutrition and dietary health doesn’t seem to have changed much over the years: everything in moderation.

Isabel Hardman