Thursday, July 30, 2009

This Blog May Contain Nuts! Allergic Reactions

There is a big difference between eating well and eating healthily.

There is an even bigger difference between a minor intolerance to food and a full blown allergy.

If you do have a real food allergy, then take heart, more and more research is taking place on the subject and an interesting picture is emerging.


Better food labeling is thought to help but it also sometimes confuses and deceives. Independent tests on labeled and unlabeled foods showed an alarming inconsistency between the contents and the information on the label. Dangerously so, in some cases.


This misinformation on labels is often prompted by the fear of litigation. So, the suppliers adopt a 'better safe than sorry' mentality, which is not at all helpful for consumers.

Anaphylaxic Shock

Even if the food industry does find a better way to label foods, there will always be the danger of an accidental exposure to high concentrations of an allergen. "The main risk is from caterers and restaurants," says Frans Timmermans of the Netherlands Anaphylaxis Network.

"In the UK most deaths are from curries, weddings, parties, and not knowing what ingredients are in satay and pesto. Otherwise, it's often down to not knowing that you are allergic in the first place." The first time you discover it can be a shock.

More People are Allergic to Hazelnuts than Peanuts

A Passing Exposure

Some people with a severe food allergy are afraid of even a passing exposure to an allergen, and this has led some to ask for bans of potentially dangerous foods in public areas such as schools, to reduce the risk.

Some American high schools, for example, are now banning food products containing peanuts. In one instance, a school bus was evacuated and then taken out of service to be decontaminated after a single peanut escaped from its wrapper. "People in favour of various bans feel it is just easier to have the food eliminated," says Scott Sicherer, an allergist at the Mount Sinai School of Medicine in New York City.

Proportionate Response

Others believe that such measures are out of proportion to the real danger. Writing in the medical journal BMJ last year, medical sociologist Nicholas Christakis of Harvard Medical School in Boston observed that efforts by US schools to prevent students being exposed to peanuts "represent a gross overreaction to the magnitude of the threat" (BMJ, vol 337, p 1384).

According to Timmermans, parents can sometimes become so worried about the possible threat to their children that they cause the children themselves psychological distress.

Timmermans says his daughter, who is also highly allergic to peanuts, would be able to sit next to someone eating a peanut dish without experiencing a reaction. Although he admits, it would make her very uneasy.

How to test for allergies

There are three main or approved methods to test for an allergic reaction and these should be done under strict medical supervision:

  • The skin-prick test: A drop of a solution containing the suspected allergen is placed on the skin of the subject's forearm, which is then pricked with a needle. A positive reaction is indicated by itchiness and a reddening of the skin, or a white swelling.
  • Blood tests: High levels of allergen-specific antibodies in the blood indicate an allergy.
  • Food challenges: Research teams from the EuroPrevall task force are using a chocolate dessert which can be spiked with an allergen without a noticeable change in flavour. Each team feeds its subjects increasing amounts of the dessert at 20-minute intervals, containing allergen doses ranging from 3 micrograms to 3 grams, until the subject reacts - for example with a skin rash or swelling. The placebo, identical except that it contains no allergen, is administered in the same way but on a different day.

What is a food allergy?

Our immune system is meant to protect the body from invading parasites, bacteria and other foreign substances. Sometimes it overreacts to what should be a perfectly innocuous food or other substance, causing an allergic reaction.

IgE Antibodies
Most people who suffer from a food allergy have immunoglobulin E (IgE) antibodies that are primed to respond to the allergen involved. In the presence of the allergen, the IgE antibodies activate mast cells around blood vessels and in the skin. Histamine released by these cells causes small blood vessels to dilate, giving rise to the well-known symptoms such as itching and swelling in the mouth, skin rash, itchy or runny nose or diarrhoea.

Severe Shock
The most dangerous result is anaphylaxis, a whole-body reaction which can end in a catastrophic fall in blood pressure combined with breathing difficulties, sometimes resulting in death.

Coeliac Disease
Not all food allergies are mediated by IgE. Perhaps the best known of this other group is coeliac disease, an allergy to proteins present in the gluten of wheat, barley and rye. It is caused by an overreaction by the immune system's T-cells, which damages the lining of the gut. Sufferers endure diarrhoea, loss of weight and potentially malnutrition.

Food Intolerance
True food allergies should not be confused with "food intolerances". Rather than being caused by an overenthusiastic immune system, milk intolerance, for example, results from a lack of the enzyme the body needs to break down lactose, the main sugar in milk. Symptoms include nausea, abdominal pain and, once again, diarrhoea.

Building your resistance

While the symptoms of an allergic reaction to foods can be treated, there is no accepted therapy to prevent the reactions in the first place.

There may be hope, for those with a peanut allergy at least. A team from Addenbrooke's Hospital in Cambridge, UK, recently exposed four children to a daily dose of peanut flour, starting with just 5 milligrams. This year they reported that by the end of the six-month trial the children were able to tolerate 10 whole peanuts a day (Allergy, vol 64, p 1218).

If you or a friend or family member have a peanut allergy, please do not try this at home. Always consult with your doctor or with a specialist before taking risks with your health.

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