CULINARY ACCENT

Individuals with food allergy develop symptoms after eating foods that for the vast majority of the population are part of a healthy diet. The only way for the allergic individual to manage food allergy is to avoid eating the food that causes the allergic reaction. The level of avoidance required may seriously impair the quality of life of the food allergic individual. The impact also extends to the people (e.g. family, friends, teachers) around the allergic individual, as all have to be vigilant to protect the allergic individual from the foods, which may trigger an allergic reaction. For that reason, the quality of life of a significant part of the population may be affected by food allergy. We cannot know the extent of the problem without knowing the percentage of people with food allergy in the community. Many people believe that the percentage of people with food allergy is increasing. However, with few exceptions we do not have any data that can clarify whether this is in fact true. It is a clinical impression that the occurrence of food allergies changes with age and varies across different geographical areas, for example, because of different dietary patterns. If indeed such variations exist, it would be a great help for researchers who are trying to find out why some people develop food allergies.

 

Most studies performed in a representative sample of the population have used questionnaires to ask people if they believe they are allergic to food. The quality and results of such studies varies depending on the quality and design of the questionnaire. Some studies have used short questionnaires based on as little as 2 questions while others have used a screening questionnaire combined with an interview to confirm suspicion of food allergy. Different questions may give different results. The question: “Have you ever had a food allergic reaction?” gives a different result from: “Have you had a food allergic reaction during the last year?”. Studies with self-reported food allergy will tend to overestimate the percentage of people with food  allergy in the community, as you might not be able to tell the difference between allergy and other reactions to foods as the symptoms may be similar.  When medical specialists diagnose food allergies they will as a first step talk with and examine the patient for signs of allergic symptoms.

 

This information will help the specialists decide which tests are appropriate. The first test isusually a test for the detection of IgE antibodies to different foods.  Normally we produce IgE antibodies to fight infections caused by parasites. In some people for yet not known reasons the immune system produce IgE antibodies to harmless things like foods. Skin prick testing and blood tests are the main tests used to detect food-specific IgE antibodies. The presence of IgE antibodies to a specific food indicates that this person may experience allergic symptoms when eating that particular food. However, it is possible to have specific IgE antibodies without developing symptoms. Therefore, it is normally necessary to perform a provocation or challenge test with the suspect food to confirm a food allergy. This involves introducing the food to the patient in gradually increasing amounts under controlled conditions. Many specialists believe that the challenge test is the gold standard to diagnose food allergy. Others may make a diagnosis based on convincing symptoms and a positive test for food-specific IgE antibodies as it is not always feasible to use the challenge test. Different kinds of skin prick and blood tests exist, and the food challenge test may be performed in different ways in different studies. These factors explain the huge diversity of study designs to assess the percentage of people with food allergy.

 

The genes of food allergy

Some genes possibly have a specific role in allergic responses to foods. For example, these may be genes coding for molecules with a role in the immune system or with a role in the breakdown of food proteins in the gut.

 

Breakdown of food allergens

The food we eat needs to be digested into small molecules before our bodies can make use of it. In general cooked foods are more digestible than raw foods. The food is first broken down into smaller particles when we chew it. Enzymes in the gut, along with acid in the stomach, are essential for the final breakdown of food into its component parts.  If the food is not broken down properly in the gut it may be that food allergens are made available for the gut immune system in a way that promotes their allergenicity. Therefore, individuals with reduced stomach acidity (e.g. because of anti-acid treatment) may be predisposed to becoming food allergic or it may worsen the symptoms of a pre-existing food allergy. Infants may be more susceptible to developing food allergy because they have an immature gut.

 

The gut immune system

Cells of the immune system are distributed all over our body in organs such as the bone marrow, spleen and lymph nodes. However, the highest numbers of immune cells surround our gut. It is generally accepted that the gut immune system plays an important role in the development of IgE-mediated food allergy. However, we know very little about how it may do this.

 

For most people the gut immune system learns to recognise food allergens as harmless, and they never suffer from an allergic reaction. The age infants first meet food allergens e.g. in solid foods, and the amounts they eat may both be important. However, we do not know how much of a food we need to eat (e.g. in breast milk or solid foods) or to take up through other ways (e.g. via the placenta, the skin or the lungs) in order for our immune system to either become allergic or to regard the food as harmless.

 

Microorganisms of the gut

As foetuses we have a sterile gut. During birth and rapidly thereafter, bacteria and other microorganisms from the mother and the surrounding environment colonize the infant gut. The gut of healthy children and adults is colonized with hundreds of different species and several kilos of beneficial bacteria. Research suggests that these microorganisms are involved in a range of useful functions, such as teaching the gut immune system to recognise foods as harmless.

 

It is therefore likely that changes in the composition of bacteria in the gut (e.g. caused by antibiotics) may be important in the development of food allergy. It has been noted that allergic and non-allergic infants have different mixtures of bacteria in their guts. Researchers have therefore tried to prevent allergy by changing this mixture. This is an area of much debate in the scientific world and, as the results of such studies are often unclear. We still need more research before recommendations about allergy prevention can be made.

 

More Information

Dean D. Metcalfe, Hugh A. Sampson, Ronald A. Simon (2003) "Adverse Reactions to Foods and Food Additives". Food Allergy, Third Edition, Blackwell Publishing.