Victims of food allergy are among the worst served by medicine, according to one of the largest reviews of research into the condition.
Allergy tests give misleading results, patients are misdiagnosed and most research is of poor quality. Among over 12,000 studies identified since 1988 just 72 were considered of high enough quality to be included in the review.
Up to 30 per cent of people claim to have a food allergy but when subject to blind testing fewer than 10 per cent actually have one. Some of the hallowed principles of allergy avoidance, such as that breast-fed babies have fewer allergies or that babies should not eat certain foods like eggs for the first year of life, turn out to have little evidence behind them.
Many adults are eliminating foods from their diet because they suspect they are allergic to them without proper evidence. Parents are denying certain foods to their children, despite the fact that most will grow out of their allergies.
The findings, published in the Journal of the American Medical Association, are the first stage in a project aimed to impose order on the chaos of food allergy testing, organised by the US National Institute of Allergy and Infectious Diseases. The institute plans to issue guidelines defining food allergies and giving criteria for diagnosing and managing patients next month.
The commonest allergies are to cow's milk, egg, peanuts, fish and shellfish. The review found whereas 3.5 per cent of people reported having an allergy to cow's milk, when tested the proportion dropped to less than 0.9 per cent. For shellfish 1.1 per cent said they were allergic but testing showed half, 0.6 per cent, were actually allergic.
However in the case of peanut allergy, the proportion who said they were allergic – 0.75 per cent - exactly matched that shown in testing. Part of the problem is a confusion between food allergy and food intolerance. A genuine food allergy is caused by an immunological response to a food, which may cause a skin rash or diarrhoea. In extreme cases, an allergy can induce anaphylactic shock, the life-threatening reaction that requires emergency treatment with adrenaline. Food intolerance may be triggered by substances in the food, which can be serious, or it may be a psychological response that has resulted from an association between a food and a bout of illness.
Pamela Ewan, consultant allergist at Addenbrooke's Hospital, Cambridge, said: "In the UK, 4 per cent of adults and 5-6 per cent of children are thought to have a food allergy. Many more believe they have one – up to 30 per cent. Some are completely wrong. But people can have a real problem with foods even though it is not an allergy. Gluten sensitivity [to cereal grains] and lactose intolerance [to milk] can make people really ill."
One of the commonest misconceptions is that a positive test for IgE antibodies – indicates an allergic reaction to a food. The immune system tends to react to certain food proteins during development, producing IgE antibodies (Immunoglobin E), but these may be transient and have no long-term effects. Having IgE antibodies in the blood after consuming a particular food does not mean that an individual will react badly to the food. Allergy tests such as those for IgE antibodies, and the skin prick test in which food is injected under the skin to guage the reaction, are meaningless on their own but are often interpreted wrongly.
Dr Ewan said: "The chaos is massive in the UK. Doctors untrained in allergy are having to pick up cases in gastroenterology clinics, asthma clinics, dermatology clinics. They send off a test and it comes back positive for IgE antibodies. But it has to be interpreted. A test without good quality information is misleading."
"People get the wrong advice because the tests are not understood. Having the test in the wrong hands without knowing what it means, causes chaos."
"The key problem is that we haven't got enough people who understand allergy. There are 30 consultants nationwide and just 12 training posts, not even enough to replace those who are leaving."
Methods to tackle food allergies (or intolerance)
The offending food is removed from the diet. Easy if it is something eaten less often, such as shellfish. It is more difficult if it is gluten, which is present in all cereal grains and all products made with them – such as bread.
Alters the body's immune response by gradually increasing doses of the food trigger. May be either oral or subcutaneous (injected under the skin). Danger of a severe reaction can be reduced by starting with a tiny dose.
Using an alternative, eg, soya instead of cow's milk. Some parents feed their babies infant formula, not based on cow's milk.
When combined with an elimination diet, drugs such as thymomodulin or cromolyn reduced allergic reactions. Among sufferers with peanut allergy, one new drug, TNX-901, raised the threshold for a reaction from half a peanut to nine peanuts. Astemizole decreased symptom severity in patients challenged with trigger foods.
Telling people what to eat, and what not to eat, and how to recognise when an allergic reaction is occurring, helps reduce the strength of the reactions.