Food intolerance can lead to conditions such as headaches, digestive disorders and weight problems and common triggers are lactose, gluten and shellfish, although the list is extensive.  Food allergy, on the other hand, can be more serious and life threatening.  There are a number of tests that can be performed to ascertain whether there is an underlying problem with a particular food or group of foods and a professional practitioner will use these along with talking over the lifestyle and family history of the individual to help improve their health.