Food

Food allergies

Updated 01 Jun 2010
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Introduction

Many people avoid certain foods because they believe they have a food allergy. But in reality food allergies only affect a small percentage of the population.

In this report, we discuss the differences between food allergy and intolerance – and try to make sense of food-allergen labelling.

How common is it?

Child eating

According to Allergy New Zealand, as many as 10 Kiwi babies are born every day who will go on to develop a food allergy. Overseas studies indicate an increase in prevalence and more young children in New Zealand are being referred to clinics for diagnosis, monitoring and support.  

Allergy has tended to be a developed-country problem. The reasons for this are complex, but some experts believe our immune systems don't have enough to do in the hygienic environments we've created ... and if the developing immune system doesn't have sufficient diseases to fight, it starts a scrap with the first allergens it most frequently comes into contact with. In babies, that could be allergens in breast milk, infant formula, or first solids.

Immunologists (allergy specialists) estimate between 6 and 8 percent of children have food allergies, and that 2 to 4 percent of adults do. Fortunately, most children will outgrow their allergy. But allergies to peanuts, fish, and shellfish tend to be lifelong.

Kids and additives and colourings

Many people believe their children have an allergy to artificial food colourings and additives. But these reactions aren't allergies. They're allergy-like intolerances or additive intolerances (see Allergy or intolerance?).

There's also a lot of debate about food colourings causing hyperactivity in children. It's hard to give a definitive answer because the many studies examining the links are difficult to assess. But an Australian expert committee concluded that "well-designed studies have failed to show a consistent relationship between a range of behavioural problems in children and the consumption of food additives".

Allergy or intolerance?

Fish

Allergy

A food allergy occurs when the immune system reacts to a food that the body mistakenly believes is harmful. Because the body perceives a threat, it produces immunoglobulin (IgE) antibodies. The IgE antibodies stimulate cells to release histamine and other chemicals, which causes the allergy symptoms.

Severe allergies are usually obvious. Contact with the mouth can cause itching and swelling within minutes, vomiting, cramps, or a life-threatening anaphylactic shock. Milder allergies can aggravate eczema and be harder to identify.

Common allergens
Peanuts

Virtually all allergens are proteins. Peanuts, soybeans, cow's milk, fish, shellfish, egg, wheat, and tree nuts (such as cashews, almonds, or pine nuts) are responsible for 90 percent of food allergies. In some cases, just a tiny amount can trigger a reaction.

Peanuts are the leading cause of severe allergic reactions. Milk, egg, and wheat allergies are the most common in children - but many children tend to grow out of them by the time they're four or five.

Sesame seeds are a fairly new allergen. This may be linked to more frequent use of sesame oil in cooking, and a higher consumption of Asian food and Middle Eastern food – which includes tahini (sesame-seed paste).

Food intolerance

Soy

This is a food reaction that doesn't involve an immune response. Food-reaction symptoms have different causes – an enzyme deficiency, a reaction to a toxin in a food, or a side effect from a chemical in a food. Often the cause isn't known and may be psychological.

Symptoms may be similar to an allergic reaction, although they are often slower to occur and more varied. These symptoms tend to be dose-related (unlike those of a food allergy). So a lot of the offending food will make you much worse than a little. It's rare that a food intolerance is life-threatening, however.

So, what are these intolerances? An enzyme-deficiency intolerance occurs when a person doesn't produce a particular digestive enzyme, or produces only a small amount of it. So certain foods won't be digested properly.

Lactose intolerance is an example of this. The gut doesn't produce enough of the enzyme lactase, which is needed to digest lactose (the sugar in milk). Drinking milk or milk products may lead to wind, stomach discomfort, and diarrhoea.

Wheat

Other people may have allergy-like intolerances. These are reactions to foods that commonly cause allergy but don't involve the immune system. For example wheat gluten can sometimes upset people with sensitive bowels, and they may need to watch how much bread they eat. But this is different from coeliac disease, a condition where the sufferer can't eat gluten because it isn't digested normally and damages the bowel wall. People with coeliac disease must remove all gluten from their diets.

Natural and artificial chemicals in food can bring on food-chemical intolerance, which causes discomfort in some of us.

One example is MSG (monosodium glutamate) – a flavour enhancer that's also found naturally in most foods. Artificial MSG is often added to soups, sauces, and Chinese food.

Additive intolerance may be associated with migraines, and with intestinal or respiratory problems. Most people tolerate the use of sulphites as preservatives in food - but those who have additive intolerance experience a range of different responses, including asthma.

Foods such as caffeine, spices, garlic, and dried fruit may be irritants – they upset the digestive system and cause diarrhoea, abdominal pain, or bloating.

Labelling

Reading a label

Some allergies are life-threatening – think of peanuts and bee stings – and so it's great news that our labelling laws require common allergens to be stated on food labels. What's not so great is the current confusion surrounding those requirements.

The Australia New Zealand Food Standards Code says that a food containing peanuts, tree nuts, milk products, fish, shellfish, eggs, wheat, gluten, sesame seeds, soy, or certain bee products must declare it on the label. This applies even if the ingredient is in the tiniest amounts. Added sulphites must also be declared when they're in concentrations greater than 10mg/kg.

Where this is going wrong is that many manufacturers are putting "may contain" statements on their products – to warn consumers about the potential for cross-contamination associated with products. This doesn't always help consumers, though, because there's no consistent definition for "may contain" statements. Different companies use different risk thresholds to decide when to label a potential allergen. The same statement may not mean the same from company to company.

Some statements are also pointless. For example, a product that states "may contain peanuts" when peanuts are an ingredient.

The food industry says it's between a rock and a hard place. Companies have to choose between guaranteeing a food is free of an allergen, and covering themselves because of the risk of allergen contamination.

Labelling working group

The industry recognises this is a problem and has formed The Allergen Forum Labelling Working Group.

The working group has developed Voluntary Incidental Trace Allergen  Labelling (VITAL), a standardised allergen risk assessment tool for food producers. VITAL encourages the consistant application of a single precautionary statement. Food assessed using VITAL will say an allergen "may be present" on the packaging. 

Unfortunately, VITAL is voluntary and there is no logo on products advising if they have been assessed using VITAL. Allergy New Zealand also shares these concerns. We would like the whole food industry to adopt VITAL so consumers get consistent information about contamination risks.

Manufactured food database

Many companies also supply information to the Manufactured Food Database (MFD). The MFD is managed by the New Zealand Food Safety Authority and gives information on the composition of almost 6000 foods. It lists ingredients, additives, the presence or absence of common allergens, and nutrition information.

You can go to the MFD website and check on various foods.

The MFD is updated during the year as new information comes in, and annually through a survey of manufacturers. You still need to check food labels regularly, because manufacturers may change ingredients or manufacturing processes and there may be a delay in updating the MFD.

Working out if it's an allergy

Foods can upset people for many reasons. If you break out in hives, or wheeze or vomit after drinking milk, you probably have a milk allergy. But if you feel bloated or get an upset stomach, you probably have lactose intolerance. (See Allergy or intolerance?)

You need to find out whether the symptoms are those of an allergy or an intolerance, so that you don't unnecessarily restrict your or your family's diet or pay for tests that won't make any difference.

The gold standard for diagnosis is a double-blind placebo-controlled food challenge. But because this is time consuming and needs to be carried out in a hospital setting, it isn't always practical.

Your doctor may refer you to an allergy clinic. An allergy specialist (immunologist) will take a clinical history, do a physical examination, and test for allergy.

Testing procedures

Skin prick and RAST (radioallergosorbant) tests are the main medical testing procedures.

Skin prick test

The skin prick test involves small drops of potential allergens being placed on your arm (or back, if you're a small child). A tiny prick is made in the skin so the allergen comes into contact with the tissue. A red and raised area will develop around the drop you're allergic to.

In a RAST blood test, a blood sample is mixed with a food extract and the levels of allergic antibody are measured. This test indicates you are sensitised to an allergen, but it may not necessarily mean you'll have an allergic reaction.

Alternative practitioners promote various tests, although orthodox allergy specialists say these tests are inaccurate and don't have any scientific basis. Unproven tests include applied kinesiology (muscle testing), hair analysis, iridology, and pulse testing.

Unfortunately, there aren't enough allergy specialists in New Zealand to manage the burden of allergic disease and there's still a long waiting list to see one in the public hospital system. If you have health insurance with specialist cover, you may be able to claim for the cost of your consultation and tests.

Prevention and treatment

Prevention

There's no strong scientific evidence that you can prevent food allergies by restricting your child's diet early on. But it may be possible to delay the onset in susceptible children.

Breastfeeding has been shown to protect against allergies. When allergies run in the family, it's recommended that mothers use only breast milk until the child is at least six months old.

You may also want to delay the introduction of dairy products, eggs, and wheat for at least one year - and tree nuts and fish for three years - if there's a family history of allergy. And if the allergy is peanuts, avoid these until the child's at least three years old.

Treatment

The most effective way to avoid an allergic or intolerant reaction is to cut out the food altogether. Make sure you talk to a doctor or dietitian about identifying the food that's causing the reaction - and get advice so that you don't miss out any essential nutrients from your diet.

If the allergen causes a severe reaction, it may put the whole body into shock. This is called anaphylaxis, and it needs urgent medical attention. People with severe allergies are advised to carry an adrenaline injection (which reverses the effects of anaphylaxis) and seek emergency medical attention. Anaphylaxis is uncommon with the first exposure to a food allergen; it usually occurs after you have been sensitised to an allergen.

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