In food allergy, an abnormal immune

In food allergy, an abnormal immune system response results in the body making antibodies to 'fight off' a food. However, some people suffer symptoms after eating certain foods even when they are not producing antibodies against them. A variety of different mechanisms can cause foods to affect people in this way. Food allergy, either IgE antibody mediated or delayed non-IgE mediated allergy are reactions caused by the immune system, which affects approximately 1% of adults and 5-9% of children in the UK.

FOOD INTOLERANCE is much more common than food allergy and is not caused by the immune system. The onset of symptoms is usually slower and may be delayed by many hours after eating the offending food. The symptoms may also last for several hours, even into the next day and sometimes longer. Intolerance to several foods or a group of foods is not uncommon, and it can be much more difficult to decide whether food intolerance is the cause of chronic illness, and which foods or substances may be responsible.

In allergy, the patient cannot usually tolerate even a small amount of the offending food without suffering symptoms, as it only takes a tiny amount to trigger a response from the immune system, which makes it very easy to diagnose. Also, tests for specific IgE are easy to perform and reliable so the diagnosis can usually be readily confirmed.

With food intolerance, some people can tolerate a reasonable amount of the food, but if they eat too much (or too often) they get symptoms because their body cannot tolerate unlimited amounts.

The symptoms caused by food intolerance are varied. They usually cause gastrointestinal symptoms such as bloating, diarrhoea, nausea, vomiting, irritable bowel and can include skin rashes and sometimes fatigue, joint pains, dark circles under the eyes, night sweats and other chronic conditions.

Food intolerance can have a number of different causes:

Enzyme defects

Enzymes are required to help with the breakdown of natural substances found in certain foods. If these enzymes are missing, or in short supply, then eating the food can cause symptoms because part of the content of the food cannot be properly dealt with by the body.

In lactose intolerance, for example, the body lacks the enzyme (lactase) that breaks down lactose (milk sugar) into smaller sugars ready for absorption from the gut. Lactose is too large to be absorbed across the gut wall undigested, and its presence in the gut causes gut spasm, pain, bloating, diarrhoea and 'failure to thrive'. Incidentally, these same symptoms can occur in milk allergy, when the body has made antibodies to milk protein, which causes an immune reaction when you drink milk. Hence, you cannot always distinguish allergy from intolerance by symptoms alone without expert help.

Most foods require some enzyme activity in their digestion, and enzyme deficiencies can be an important factor in food intolerance.

Pharmacological

Some foods contain naturally occurring chemicals that have an effect on the body, such as caffeine in coffee, tea, and chocolate, or amines in certain cheeses. Some people seem to be more affected than others by these natural substances in the food, causing symptoms which would not occur in other people unless they ate far larger quantities of the food.

Toxic

A number of foods contain naturally occurring substances that can exert a toxic effect, causing symptoms of vomiting and diarrhoea. In cases such as kidney beans or chick peas that are undercooked, there are aflotoxins, which cause these symptoms. If they are cooked fully the toxins are not present. This is very confusing to someone who seems to tolerate a food sometimes but not others.

Histamine in foods

Some foods contain histamine naturally, and others (such as certain fish that are not fresh or have not been stored properly) can develop a build-up of histamine (in fish, called histadine) in their flesh as they age. In certain people, this histamine occurring naturally in the food can cause symptoms when the food is eaten; typically, rashes, stomach pains, diarrhoea and vomiting and in some cases symptoms that can mimic anaphylaxis.

Salicylates in foods

Many foods naturally contain salicylates, and our tolerance to this can vary. The vast majority of people can eat salicylate-containing foods with no problems, but other people may suffer symptoms if they eat too many foods, which when combined contain a large amount. These salicylate-intolerant people will get better if they eat a diet of low and moderate salicylate foods and avoid those with the highest levels.

Additives in foods

A wide variety of natural and artificial additives are used in colouring, preserving and processing foods. Some people can suffer symptoms provoked by hypersensitivity to food additives.

How is Food Intolerance recognised?

Certain features such as the pattern and type of symptoms can help to distinguish food intolerance reactions from those that might be a result of food