Food intolerance is a kind of food sensitivity. It is an inability of the body to properly digest certain foods. This causes an adverse reaction every time that particular food or ingredient is eaten, and especially if large quantities are consumed.
 Why should I be aware of this?
Food intolerance is different from food allergy. A food allergy, like other allergies, is an immune system response. Food intolerance, on the other hand, is linked to digestion as it is a response of the digestive system. It occurs when a person is unable to properly digest or breakdown a particular food as the gastro-intestinal tract is unable to produce appropriate enzymes for normal chemical breakdown. The food passes through unprocessed, or lingers in the gut fermenting, producing excess gas. Thus, the food might pass right through the body before digestion is complete, and so it is eliminated only partially processed. In other cases of intolerance, the unprocessed food remains in the digestive tract and attacks the lining of the gut and damages it every time that food is eaten.
Food intolerance is generally not life threatening like food allergies can be. However, if someone eats a food he is intolerant to, it could make him feel ill or affect his long-term health. Fortunately, most food intolerant people recover fully when the offending food is avoided.
 All about food intolerance
The absence of a specific enzyme in the body may increase toxic by-products and histamine, resulting in the symptoms of allergy. Since it is not actually an allergy, it is called a 'pseudo-allergic' reaction.
Food intolerance doesn't include psychological reactions to food. Disliking a food is not being intolerant to it and neither is it the same as food poisoning, which is caused by toxic substances present in food.
 Intolerance to lactose
Intolerance to lactose, which is found in milk and other dairy products, is the most common food intolerance. It is caused by the absence of lactase, which is the enzyme that processes a certain kind of sugar called lactose that is present in milk. Without this enzyme, the milk sugar lactose cannot be broken down into simpler forms that can be absorbed into the bloodstream. Lactose intolerance can cause symptoms very similar to Irritable Bowel Syndrome.
Another common example is a deficiency of an enzyme called aldehyde dehydrogenase, which is needed to break down alcohol. When people suffering from this enzyme deficiency drink even small amounts of alcohol, they feel unwell.
Some people have adverse reactions to chemical preservatives and additives in food, such as sulphites, benzoates, salicylates, monosodium glutamate, caffeine, aspartame and tartrazine.
 Symptoms of food intolerance
Symptoms of food intolerance include digestion-related problems like nausea, stomach pain, gas, cramps or bloating, vomiting, heartburn and diarrhea. However, there can be a number of other problems associated with food intolerance that are not directly digestion-related symptoms. If the food we eat is excreted without being properly digested, that means that many useful nutrients are also not absorbed by the body. Thus, many food intolerant peeple do not get utilise the full nutrition from the food they eat. This may lead to many problems linked to deficiencies, such as of essential minerals like iron or calcium — which are manifested as anaemia and osteoporosis respectively — dry skin, fatigue, hair and nail diseases, weight loss, etc.
Many food intolerant people are underweight as they are not able to get full nutrient value from foods. Others can be overweight due to fluid retention — possibly an auto-immune response caused by eating foods that the body reads as poisonous.
 How common are food intolerances?
Food intolerances are quite common. In fact, nearly everyone at one time has had an unpleasant reaction to something they ate. However, some people have specific food intolerances. A strong genetic predisposition has been found to be associated with specific food intolerances. Asian, African, Mediterranean and Native Americans are strongly predisposed to be lactose intolerant — it is suggested that as high a proportion as 70 per cent to 90 per cent of these populations are affected, whereas only 10 per cent to 15 per cent of Western Europeans and north Americans are lactose intolerant.
 What can I do?
There isn’t a cure for food intolerance, so the best option is to avoid the food you are intolerant to. Identifying the food to which you are intolerant is a tedious process. To test food intolerance is a long and tedious process — you need to remove the food from your diet and see if the symptoms improve. Then reintroduce the food and check if the symptoms return. If they do, you are most likely intolerant to that food. But it is usually practically difficult to eliminate the suspected food products. Also, it is thought that we can actually be addicted to the foods to which we are intolerant. It may, therefore, be prudent to examine these can’t-live-without foods as possible suspects.
 References and Useful Websites
- Allergies Guide
- Food intolerance
- Food allergy and intolerance