The causes of food allergy
Our knowledge about the causes of food allergy is limited. Scientists suspect that certain genes, as well as conditions in the stomach and gut may play a role in the development of food allergy.
With knowledge about the causes of food allergy we might be able to prevent some cases of food allergy. We also might be able to provide new advice on how to manage food allergy.
Food allergies and allergic diseases in general probably share many risk factors. Nevertheless, some studies suggest that there are causes of food allergy that are unique and which exist in addition to the causes shared more generally with all types of allergic disease. Some of these are described below. They are ideas presented by scientists but are unproven.
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.
Dean D. Metcalfe, Hugh A. Sampson, Ronald A. Simon (2003) "Adverse Reactions to Foods and Food Additives". Food Allergy, Third Edition, Blackwell Publishing.