Unforced error? Novak Djokovic’s gluten intolerance diagnosis was made using the non-medical technique of kinesiology. Photograph: Tony O'Brien/Reuters
Serious food allergies are rare, while intolerance of many common foods – from dairy products to gluten in bread – is increasing. Are we in the midst of a health craze or something more complicated?
You know the scenario: you invite some friends over for dinner and they graciously accept. But then the caveats begin: "Elspeth is gluten- and dairy-intolerant, and I don't eat meat, fish or eggs."
Bread, milk, butter, cheese " the nation seems to have become intolerant of the foods that used to be household staples. Entire supermarket aisles are now devoted to "free-from" products, with the British market for gluten-free alone expected to grow to "£561m by 2017. Whether it's due to a genuine rise in food allergies, or simply because of a perception that "free from" is healthier, the trend for dairy- and gluten-free seems here to stay.
Yet humans have been eating wheat and dairy products for millennia, apparently without harm. Has something changed, or are the "free-from" advocates taking us for an expensive " and rather joyless " ride? Part of the confusion stems from a muddling of the distinction between food allergy and intolerance. Food allergies do seem to be on the rise, but these are different from intolerances, for which there is no strong evidence of an increase " and in some cases, no specific medical explanation for their cause. A 2008 study published in the journal Allergy revealed that although 34% of parents reported food allergies in their children, only 5% of children were found to have a genuine allergy.
So what is the difference? Allergies, such as reactions to specific proteins in wheat or milk, involve the immune system, and can be life-threatening. Symptoms usually kick in within minutes of eating a problem food, and can include vomiting, lip swelling, a rash, wheeze, and a blocked or runny nose. They are also relatively rare " at least among adults. According to an Australian study, wheat allergy affects around 0.2% of adults, while cow's milk allergy affects 0.1-0.5% of adults. For children, research suggests 2-3% of babies are affected in their first year of life.
Then there's coeliac disease, which affects 1% of the population, and is an autoimmune condition that causes serious harm if sufferers eat even small amounts of gluten-containing foods. Antibodies are generated against the gluten, but these also attack cells lining the gut, resulting in malnutrition.
Food intolerances, on the other hand, tend to generate symptoms such as bloating or abdominal pain, and these set in more slowly " sometimes several days after eating a problem food. They also aren't thought to involve the immune system. "Although a lot of the symptoms can be very unpleasant, they generally aren't life-threatening and don't do any lasting damage," says Maureen Jenkins, clinical director of the charity Allergy UK.
Among the most commonly reported intolerances are those relating to dairy and gluten, but precise numbers are difficult to obtain because studies often rely on people self-reporting sensitivities to these foods. And while reliable diagnostic tests exist for food allergies and coeliac disease, there are no reliable tests for food intolerances (with the exception of that for lactose). That's not to stop them being marketed, though.
Other tests may sound more scientific, but they're not necessarily any more reliable. Take IgG (immunoglobulin G) testing, which looks for antibodies against food substances in the blood. Unlike IgE antibodies that mediate allergies, IgG antibodies are produced by most of us in reaction to the foods we eat. But, "there is no evidence that food-specific IgG antibodies are involved in any disease processes," says Stuart Jones, principal biochemist at King George hospital, London.
The European Academy of Allergy and Clinical Immunology similarly states that IgG testing "does not indicate food allergy or intolerance". And Tariq el-Shanawany, consultant clinical immunologist at Cardiff and Vale NHS Trust, says: "For the patients I've seen who have had it done, it hasn't given them the answer that means their symptoms go away."
That's not to say that intolerance to food substances such as gluten doesn't exist. Approximately 13% of British adults claim to experience symptoms when they eat gluten-containing foods, according to one recent study " yet only 0.8% of the population have been formally diagnosed with coeliac disease. "There are non-coeliac patients who are reporting symptoms when they eat gluten. If you look at their gut tissue using a high-magnification microscope, you can see the small bowel is having a very rapid response to it," says David Sanders, consultant gastroenterologist at Sheffield Teaching Hospitals NHS Foundation Trust. "This is not an allergy or coeliac disease, but something is happening to them."
But is it actually the gluten that they are reacting to? Peter Gibson of the Alfred Hospital and Monash University in Melbourne conducted the world's first randomised-controlled trial of gluten in non-coeliacs with gut symptoms, which found they felt better when they went gluten-free. However, subsequent studies have convinced him that it's not the gluten they're reacting to, but a set of sugars dubbed Fodmaps (fermentable oligo-, di-, mono-saccharides and polyols). These sugars attract water and feed gas-generating bacteria in the small intestine, resulting in bloating, flatulence and loose stools. People with sensitive bowels seem to have worse symptoms. "There's no doubt that wheat is a major cause of bloating and abdominal problems. The trouble is that wheat has more than just gluten in it," says Gibson. Although there may be a small subset of non-coeliacs who react to gluten through some as yet undiscovered pathway, he believes that for the vast majority, reducing the fodmap content of their diet could go a long way to easing their symptoms.
But this doesn't mean they have to cut out all wheat, barley and rye, as people with coeliac disease do. "You can probably still have a schnitzel with breadcrumbs on it, but you couldn't have a bowl of pasta," says Gibson. And fodmaps are found in other foods, too: particularly onions. Eliminating all fodmap-containing foods would be the first step, but these could gradually be reintroduced until you discover the level that triggers your symptoms.
Many of those opting to buy gluten-free products aren't doing it because of abdominal symptoms, however. A recent survey of 100 British gluten-free shoppers found that 28% were doing it to boost their energy levels and 24% to lose weight; yet there's no good evidence to support these purported health benefits. "A gluten-free diet is not healthier than any other diet," Sanders says.
Starch is the main source of calories in grains such as wheat, but the starch content of wheat is similar to that of other carbohydrates, such as rice or potatoes. "I think the idea that wheat or gluten is associated with weight gain has really come from the opposite angle; if you start to cut these products from your diet, then you start to lose weight," adds Gary Frost, chair in nutrition and dietetics at Imperial College London. This is particularly true of high-calorie foods such as cakes, biscuits, or cheeseburgers.
Apart from rubbing dinner party hosts up the wrong way, giving up gluten is unlikely to cause you much harm " provided you aren't solely reliant on manufactured gluten-free products, which can be high in salt or sugar. The same can't necessarily be said about avoiding milk and dairy products, however. These provide around a quarter of our daily protein requirement and up to 60% of other important nutrients such as calcium and phosphorus. "My biggest worry about the current trend for ditching cow's milk relates to bone development in children and adolescents, and its long-term effect on bone strength in postmenopausal women," says Ian Givens, professor of food chain nutrition at the University of Reading. Dairy intolerance is at least a condition for which there's an established mechanism: approximately 65% of the world's population carries a genetic variant that means they're unable to digest the lactose in milk. Instead, this sugar passes into the small intestine where it feeds bacteria that generate gas and bloating. But lactose intolerance among Brits is less common, affecting approximately 5% of the population. Temporary lactose intolerance can also develop as a result of gastroenteritis and other illnesses, or after repeated courses of antibiotics. Even if you are lactose intolerant, studies suggest that you may be able to drink up to around 250 millilitres of milk in one sitting without symptoms, and possibly twice this amount spread through the day if consumed with food.
So why are so many people ditching cow's milk in favour of plant-based alternatives such as soy or almond milk? "I think a lot of people are buying products because they think it is trendy, or they assume those kinds of alternative milks are superior products," says Sioned Quirke, a dietitian and a spokeswoman for the British Dietetic Association. "They are not a superior product in any way, shape or form." With the exception of soy milk, plant-based milks are far lower in protein than cow's milk. And unless they have been fortified, they are also poor sources of calcium and vitamin D. There's also emerging evidence that people who consume large amounts of milk and dairy products are at lower risk of diabetes, cardiovascular disease, and colorectal cancer, possibly because of the calcium in milk. Another possibility is that widespread publicity about food intolerance is prompting many people with unexplained symptoms such as bloating or stomach cramps to self-diagnose dairy intolerance. A recent survey by Allergy UK revealed that 44% of people who class themselves as dairy intolerant have not been diagnosed as such by a doctor; instead, they have used online information or undergone non-conventional tests. Seventy two per cent have removed all dairy from their diets, even though yoghurt and hard cheese contain very little lactose and are unlikely to trigger symptoms.
Why then, are so many of us apparently eager to blame common foods for our ailments? "It's a good thing that people are more aware of conditions like irritable bowel syndrome and lactose intolerance, but I think it tends to make people jump to conclusions when they've nothing wrong with them," says Quirk. "Our bowels are very sensitive organs. If we have been ill, or if we're stressed or run down, we often will have some type of bowel symptom."
Meanwhile, leaping on the food-intolerance bandwagon, when you'd actually just prefer not to eat gluten or dairy, can make it harder for people with genuine food-related illness. "If someone goes into a catering outlet and claims that they have a dairy allergy, but then says "Well actually, I can eat some sorts of dairy but I can't eat others,' it may give caterers the impression that food allergies don't need to be taken seriously," says Moira Austin, helpline and information manager at the Anaphylaxis Campaign. "It can give people with true food allergies a bad name."
If you do suspect you have a food intolerance, a key first step is to visit your GP. This is particularly important if you believe your symptoms are being caused by gluten; the coeliac disease test for coeliac disease only works if you've been eating the stuff daily for at least six weeks.
Assuming that food allergies and coeliac disease are ruled out, removing suspect foods from your diet is the logical next step. "If your symptoms improve and you then reintroduce the food and they come back, then that proves you're intolerant," says Jenkins. And yet many people who attempt such elimination diets aren't doing them properly, she cautions: "Often people don't exclude for long enough; you need to do it for about a month. And if it doesn't make a difference, you need to reintroduce that food into your diet. Most people don't have enough nutritional knowledge to replace [foods] with other things to get the essential nutrients they need."
If you can hold up your hands and say you've been through these steps and you're certain that gluten or dairy is the source of your problems, you're probably correct: food intolerance is a real condition that deserves to be taken seriously. And, as a bonus, if you receive a proper diagnosis you may find your sceptical friends suddenly become a lot more tolerant of your intolerance.