Food Intollerance is a term commonly used for a medical condition called non-allergic food hypersensitivity.  There are three types of Food Intollerance:  Pharmacologic, metabolic, and gastro-intestinal.

Metabolic Food Intollerance is due to inborn or acquired errors during the metabolism of nutrients.  An example of metabolic Food Intollerance is lactase deficiency, where the body lacks the enzyme necessary to digest the milk sugar, lactose.  This can result in diarrhoea and other stomach upsets.  Another example is diabetes mellitus, where the body can no longer regulate glucose levels in the blood.  The first example is merely inconvenient, where the second example is potentially life threatening.

Food Intollerances can be hard to diagnose because they can mimic other problems can be delayed or dose-dependent and the substance, which is causing the reaction, can be found in many different foods.  An example of this type of Food Intollerance is phenylketonuria, which is where infants have a problem digesting a certain type of protein.  This type of Food Intollerance can, if not diagnosed and treated promptly, be responsible for retardation and early childhood death.

Pharmacological reactions can be associated with food additives such as food colouring or the preservatives added to help extend shelf life.  The reactions can resemble the reactions of someone taking certain drugs.  The most well known is the reaction to red food dye, which can be confused with hyperactivity in susceptible children.  This particular example is very hard to diagnose because the food dye is present in so many different types of food, and it can take up to 8 hours to manifest, and over two weeks to wear off.

Gastrointestinal reactions to foods not well tolerated include gas, bloating, diarrhoea, and vomiting.  Most of the symptoms will start within a half hour of ingesting the food, but can be delayed for up to 48 hours.  Irritable bowel syndrome, or IBS, is an example of a gastrointestinal reaction.  Other examples can include inflammatory bowel disease, chronic constipation, and chronic dyspepsia.  All of these conditions may be helped by a special diet, which excludes certain classes of foods.  This is called an “exclusion diet” and is known as a “Low FODMAP” diet.    This diet can provide great relief from the symptoms of IBS and of IBD, and when patients are introduced to the diet, longer term compliance is high despite the challenges of withdrawal symptoms experienced by the patients.  Some GPs are sceptical about the reasons behind the benefits, but acknowledge that the benefits are there.