Many people are changing diets in a belief that they have a food intolerance. But, Roger Dobson asks, is the diagnosis the real problem?

When man first settled down and began to grow cereals 10,000 or so years ago, it was a key moment in the beginnings of civilisation. It heralded the arrival of settlements, long-term planning, teamwork, domesticity, and an all-year supply of food. But it gave birth to something else too. The wheat that they grew for the first time sowed the seeds for what some would say is one of the biggest epidemics the world has seen, food intolerance.

According to some estimates, one in five people, perhaps even half the population, suffer with some kind of intolerance to foods as diverse as cheese, coffee, bread, milk, and yeast as well as wheat. Food intolerance is linked to conditions as varied as irritable bowel syndrome, asthma, autism, eczema, arthritis, hyperactivity and chronic fatigue syndrome, and it has also spawned a huge industry, turning out alternative diets, supplements, and self-help books and videos.

But there is now growing scepticism about the scale of the food intolerance epidemic, and an increasing concern that people may be eating an unbalanced diet as a result of omitting but not replacing what is perceived to be the trigger food. A new study by the British Nutrition Foundation suggests that only one to two per cent of adults are food intolerant, and that although around five to eight per cent of children are affected too, up to 90 per cent of them have outgrown the intolerance by the age of three. But others disagree, and say that the problem is underestimated: "Many people don't know the symptoms they have are caused by food, so the underestimate of food intolerance must be substantial," says Professor Jonathan Brostoff, professor of allergy and environmental health at King's College, London. "It is a very real problem. Patients come to the clinic who are really ill, with headaches, a fuzzy brain, irritable bowel, aching joints, and desperately tired. Put them on a diet and six to eight weeks later, they walk in, upright, pink cheeks, no longer with bags under the eyes, saying, 'Gosh, where have the last 20 years gone?' "

One of the problems with estimating the scale of the food intolerance problem is that it is often confused with food allergy. Allergies occur when the body's immune system responds abnormally to a protein found in a particular food, resulting in antibodies going on the offensive and triggering reactions such as swelling, inflammation, and irritation.

Food intolerance does not usually involve the immune system and is caused by a physical reaction to a food. In some cases the reaction is a result of the body lacking a sufficient amount of an enzyme needed to digest that food. Lactose intolerance, for instance, is the inability to digest significant amounts of lactose, the predominant sugar in milk, and coelic disease is an inflammation of the gut caused by eating cereals such as wheat which contain gluten. Large intakes of caffeine and curry can also cause gut irritations, while amines in strong cheeses, Chianti, chocolate and tomatoes can result in flushing and headaches. Food additives have been linked to provoking urticaria, rhinitis and asthma.

Allergy and food intolerance have different symptoms too. In an allergic reaction, irritant chemicals are rapidly released into the tissues, resulting in difficulties in breathing, swelling of the lips or tongue, asthma, rashes, vomiting, and a drop in blood pressure. With food intolerance, reactions usually take several hours to develop, and the symptoms are mostly non-specific, like headaches, fatigue, and diarrhoea.

Although there is little doubt that some people are intolerant to some foods, especially lactose and gluten, it is the apparent scale of the problem and the effects of the resulting dietary changes on long-term health, that are causing concern. "It is estimated that true food intolerance affects no more than five to eight per cent of children and less than one to two per cent of adults. This is much lower than the 20 per cent of people who perceive themselves to have an intolerance,'' says Claire MacEvilly, nutrition scientist with the British Nutrition Foundation, whose study reviewed what research there is. "It seems to have become the thing to do, to blame problems on food intolerance. Reactions to food are blamed for weight gain, headaches, spots, rashes and general aches and pains. Our concern is that people are excluding food from their diet and not replacing it, and their diet is becoming unbalanced.''

The foundation is dismissive of many of the diagnostic tests for food intolerance, some of which cost up to £250: "The vast majority of so-called methods of diagnosis advocated in magazines and via the internet are without scientific basis and have not been independently validated. Such tests include hair and nail assessment, electro-magnetic conductivity tests and kinesiology. At best the patient is likely just to have wasted money, at worst these tests can result in misdiagnosis and the unnecessary treatment of a disease that does not exist by the use of an inappropriate and potentially dangerous diet,'' says its report.

But Professor Brostoff says that diet is a therapy that works. "I know that if I had multiple food intolerance, I'd go on a diet, clean myself out, and add one food back at a time. You are the only barometer of your own intolerance.''