Some people are sensitive to a protein in cereals called gluten.
When eaten, gluten causes changes in the lining of the upper part of the intestine which impairs its ability to absorb nutrients from food. For many years the condition has been recognised in children and called coeliac disease, though it can manifest itself at any age. In Britain, the condition affects approximately one in a thousand people. It is more frequent in parts of Ireland. Its frequency is increased among family members of a person affected.