Adverse reactions to wheat have been more frequently reported than to other cereal-based foods. The best defined of these are coeliac disease and IgE-dependent wheat allergy, both of which result from malfunctioning of the immune system. Allergies to other cereals such as maize, sorghum and millet, are not common and are not related to reactions triggered by wheat, rye, barley and oats. As a consequence individuals with wheat allergy, including coeliac disease, can usually eat maize-based foods such as polenta. However, allergic reactions to maize can result from the fruit allergies found in the South of Europe which often start with reactions to peach.
Coeliac disease is triggered by the gluten fraction of wheat or by the gluten-like proteins found in other closely related cereals such as rye, barley. Some sensitive individuals may also react to oats. The gut reacts to the gluten and becomes smooth, loosing its ability to absorb nutrients; symptoms including diarrhoea as well as deficiencies in nutrients like vitamins. It can manifest itself in childhood, affecting children’s growth and development, or in adult hood. As there is no cure individuals with coeliac disease have to avoid eating gluten for life. However, coeliac disease does not cause the potentially fatal reaction of anaphylaxis if gluten is accidentally eaten.
In contrast IgE-mediated cereal allergies can be caused by the antibody molecule IgE binding to many proteins, not just gluten. Sometimes the reactions (often severe) only develop if an individual takes exercise within a few hours of eating wheat or related cereals, in a condition called exercise-induced anaphylaxis. Individuals with wheat allergy often react to closely related cereals like barley and rye, less frequently to the more distant relative, oats. Diagnosis of cereal allergies can be complicated by the fact that some of the blood tests for cereal food allergy can accidentally detect allergy to grass pollens instead.
As a consequence of these adverse reactions, cereals containing gluten, (i.e. wheat, rye, barley, oats, spelt or their hybridized strains) have been included in Annex IIIa of the food labelling directive along with derived products. Temporary exceptions to the labelling rule (derogations) have been granted for wheat based glucose syrups including dextrose, wheat based maltodextrins, glucose syrups based on barley and cereals used in distillates for spirits.