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Is It Really a Food Allergy Is it really a food allergy?
 Enriching the great British diet with exotic vegetables and fruits, herbs and spices has improved our image on the world food stage, but it could be proving too challenging for our prehistoric digestive systems. The plain, home cooking of the 1950s and '60s may have protected us against a range of digestive and other health problems that today's foodies are queuing up to call food allergies.
'People are exposed to a far greater variety of foods that may give them problems — and at an earlier age — than they ever were before. Four or five years ago I used to see one patient a week with a food allergy, now it may be as many as eight. Whether those allergies are perceived or real isn't always clear, but there's no doubt that more people are having problems,' explains Isabel Skypala, head of dietetics at the Royal Brompton and Harefield NHS Trust, London.
One in five people (20%) in the UK claim to have food allergies — much to the irritation of allergy experts who can find a genuine immune reaction to foods in only 1-2% of adults and perhaps 4% of children. But, if the vast majority of people who claim to respond badly to certain foods don't have allergies, what is wrong with them?
'A lot of people get symptoms after food and think it must be an allergy when, in fact, it's a digestive problem or a reaction to something else they've been in contact with,' says Ms Skypala. You also need to ask your doctor whether it would be wise to carry any medication with you for emergencies. If so, make sure friends and relatives know where it is and what to do if you have a bad reaction.
All too often, neither she nor other food allergy experts can get to the bottom of their patients' discomfort, be it breathing problems, diarrhoea, vomiting, bloating or skin rashes. A veteran of countless allergy clinics over 20 years, Ms Skypala accepts that there has been a general increase in food allergies, especially the severe anaphylactic reactions which leave people gasping for breath and in rare cases can be fatal. But she believes that digestive problems linked to our changing eating patterns and much more varied diet may be at the root of what many people call food allergies.
Quite simply, some foods may disagree with us and we should probably try to avoid them. But labelling our symptoms a food allergy is to blame our immune system and, in most cases, it's innocent.
what is a food allergy?
A food allergy, like any other form of allergy, such as asthma or hayfever, means that the immune system is over-reacting. In asthma, it over-reacts to airborne particles, such as dust mites and animal fur while in hayfever it over-reacts to pollen.
In a food allergy, some of the white blood cells that make up the immune system over react to food proteins. In allergic reactions that happen straight after eating, the white cells make antibodies, called IgE, which recognise specific food proteins each time they are eaten. When there is nothing to upset them, IgE antibodies sit harmlessly on the surface of a group of immune cells called mast cells. But if IgE antibodies see food proteins that they don't like, they will try to bind to them. The mast cells get tugged around and burst, releasing a load of immune messengers, such as histamine, that call in other immune cells and cause symptoms.
The most dramatic allergic reaction is called anaphylaxis and it happens mainly in response to food or bee venom. The mouth and throat swell up so badly that the windpipe closes down and it's almost impossible to breathe. Emergency drugs are needed to relax the throat and airways and counteract the allergic trigger.
If you ever have such severe symptoms you should find out the cause and, if a food is responsible, do not attempt to eat it again. You'll also need to tell friends and family to avoid putting the ingredient in any meals they cook for you, and to check what's in foods when you eat out.
Fortunately, anaphylactic reactions to food are rare. A recent review of fatal and near fatal incidents of food allergy in Britain's 13 million children under 16 revealed only eight deaths from food allergies over the last 10 years. Milk was responsible for four of the eight deaths reported in the study and peanuts for two deaths.
A further analysis of food allergy reports received between 1998 and 2000 showed six near fatal and 49 severe reactions to food. Peanuts were the most common cause of non-fatal reactions but were less commonly involved than in previous studies.
Tree nuts (Brazil nuts, almonds and hazelnuts), eggs, fish and shellfish, soya and wheat are other common causes of true food allergies.
Symptoms of a food allergy do not have to be as dramatic as anaphylaxis. They include lip and tongue swelling, asthmatic symptoms, such as wheezing and breathlessness, skin rashes, diarrhoea and vomiting. But, as Ms Skypala points out, these symptoms occur with other illnesses and it can be harder to link them with food, especially if they do not occur until hours or days after eating or only in unusual circumstances.
'Some people only get an allergic reaction to a food when they exercise after eating. Others have an allergy to tree pollen and this cross reacts with certain vegetables, and their lips may tingle after they eat them,' she says.
delayed reactions
Blurring the allergic boundaries still further are people who get delayed allergic reactions to food that do not involve IgE. Instead, a group of white cells called T lymphocytes appear to be involved.
'Food allergy used to be an immediate reaction but we do now see children who have a delayed reaction to milk, for example. They do not have IgE but the reaction does involve the immune system, and a lot of research is trying to find out more about this type of allergy,' says Ms Skypala.
Within this group of delayed onset food allergies, may also sit Coeliac disease — the often hereditary, inflammatory intestinal disorder caused by gluten in wheat and some other cereals. Left untreated, the damaged intestinal lining may not be able to absorb nutrients properly, leading to weight loss, diarrhoea and vomiting, tiredness and other health problems.
what is food intolerance?
If you have a food intolerance, your immune system does not over-react to something in your food. There is no change in IgE or T lymphocyte levels. Instead, you may have a specific enzyme deficiency which makes it impossible for you to digest something in your food. For example, some people do not make the enzyme, lactase, which is needed to digest the lactose in milk so that, from an early age, they vomit after drinking milk.
But most food intolerances are not caused by specific enzyme deficiencies. In fact, there is often no obvious mechanism. Thus, some children are intolerant to milk even though they have the necessary enzyme to digest lactose. They rarely vomit after drinking milk, but they still get bloating and diarrhoea.
What makes things even more complicated is that some of the foods which commonly trigger allergic reactions are also involved in food intolerance, for example milk, eggs, wheat and soya. Chocolate, caffeine, wine and some food additives are also involved in food intolerances, but do not appear to be involved in allergies.
Pasta is another common cause of symptoms. People can get very bloated, says Ms Skypala, and they assume they must have an allergy or intolerance. But, as she explains, you only have to watch pasta soaking up fluid in a saucepan to realise what it might do in the stomach.
'Some people will have a genuine intolerance but a lot of those with gastric symptoms just don't cope well with particular foods. They aren't able to digest them properly,' she says.
how can I tell what I've got?
It's easier to identify a true food allergy than an intolerance. Anyone who has a severe anaphylactic reaction should be referred to an allergy specialist for tests:
A skin prick test involves putting a small amount of the suspect food extract into the upper layer of the skin. If you are allergic to it, your mast cells will release histamine and, within 15 minutes, a red wheal will appear on your skin where the test was done.
A blood test measures the amount of IgE in your blood when a small sample is exposed to the suspect food extract. This is called a RAST or ELISA test.
These tests are also used to detect food allergies in people with less severe reactions. They are not perfect but the more severe the reaction, the more likely they are to give positive results. Allergy experts do not recommend other methods, such as IgG tests, provocation tests (when food extracts are placed under the tongue) or kinesiology (a test of muscle strength) because of a lack of scientific evidence that they work.
Food intolerances are hard to detect because of the lack of scientific tests. There is no equivalent of an IgE test. The only reliable way to detect food intolerances is to remove suspect foods from the diet and see if symptoms improve. But it is best to do this with the help of a fully trained (state registered) dietitian. Excluding one or two foods without expert help, while waiting for an appointment at an allergy clinic, may not be a problem. But, all too often, explains Ms Skypala, people end up at allergy clinics, living on little more than rice, because they have withdrawn so many foods without improving their symptoms.
'It can be very hard to diagnose the cause of symptoms but if someone does think it's a particular food, I and other state registered dietitians can help them to avoid it safely, without risking nutritional deficiencies, and that's especially important for children,' she says.
It can take several months to see a state registered dietitian on the NHS but the British Dietetics Association does have lists of properly trained private practitioners. Unfortunately, people have been able to call themselves 'dietitians' without the proper qualifications, though this is changing. However, no one can call themselves a 'state registered dietitian' if they are not properly trained.
As Ms Skypala concludes: 'Food problems are always more complicated than people think. They cut things out, feel better for a while, then feel worse again and cut more things out. They can end up on rice and apples and celery, feeling terrible because they are not getting the nutrients they need. They are always trying to get back to the way they think they used to feel, but the problem can go on for so long that they don't really remember how they felt at the beginning.'
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