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Food Intolerance

Written by Dr. Lakshmi Venkataraman
Medically Reviewed by The Medindia Medical Review Team on Feb 09, 2018

What is Food Intolerance?

Some persons experience an unpleasant physical reaction (nausea, vomiting, bloating) upon ingesting certain foods making them unwell. Adverse reactions to foods are seen commonly and can be broadly divided into two categories, namely food allergy and food intolerance. It is essential to distinguish between food allergies and other food-related illnesses because the treatment is different.

Food intolerance also termed non-IgE (immunoglobulin E) mediated food hypersensitivity or non-allergic food hypersensitivity involves difficulty in digesting certain foods. It should be distinguished from a food allergy which is an immune system mediated reaction.

Facts on Food Intolerance

What are the Common Types of Food Intolerance?

Food intolerance is a non-immune adverse reaction to certain foods. It can be broadly divided into three types.

Functional Intolerance

Functional intolerance is caused by defective function of certain digestive processes in the body. These include any of the following.

Enzyme deficiency

The most common cause is an absence of or deficiency of an enzyme needed to digest certain foods such as lactase deficiency leading to lactose intolerance. Other enzyme defects include isolated or combined disaccharide malabsorption syndrome, affecting the absorption of lactose, sucrose and other disaccharides, either singly or entirely. Also, there can be isolated galactase, maltase or saccharase deficiency.

Diamine oxidase enzyme or histamine N-methyl transferase deficiency can result in histamine intolerance.

Transporter Defects

Defective transporter molecules that transport foods into the intestinal cells from the lumen of the intestine, for example, GLUT (Glucose transporter) 2 and GLUT 5 defects. This results in a buildup of these foods in the large intestine where they are acted upon by bacteria with a resultant gas formation and bloating and diarrheal symptoms.

Structural Intolerance

The intolerance that occurs as a result of structural abnormalities in the digestive tract such as outpouchings or diverticula. Common structural defects include intestinal and colonic diverticula, lymphovascular abnormalities, and post-inflammatory strictures.

Bacterial overgrowth in these outpouchings results in the fermentation of foods with gas production and abdominal symptoms. Other causes of bacterial overgrowth include bowel resection or longterm use of certain medications, eg., omeprazole.

Active Chemicals In Foods


What are the Common Causes or Sources of Food Intolerance?

Food intolerance can be due to various foods. Some of the common food intolerances include the following Although food intolerance is not a serious condition, it can nevertheless negatively impact the quality of one's life, and it is important to identify the food or the chemical and eliminate it from the diet.

What are the Signs and Symptoms of Food Intolerance?

According to the Australian NSW Food Authority, the most common symptoms of food intolerance include the following

How do you Diagnose Food Intolerance?

It is not easy to diagnose food intolerance as symptoms of food allergy and food intolerance often overlap. It is important to distinguish between food intolerance and food allergy as the management is different.

Patients are advised to maintain a food diary and write down the list of foods eaten, type of symptoms and when they appeared. The food diary helps the doctor or dietitian determine which foods might be causing the adverse reactions and advise on steps to tackle the problem.

A detailed and careful history is important and may aid in the correct diagnosis. Points to note in the history to rule out possible food allergy include - Food Allergy Testing:

Blood and skin tests may be done to rule out food allergy. These tests will be negative for food intolerance.

In skin testing, the skin is pricked with a tiny probe coated with food extract or fresh food. The testing is usually done on the forearm or upper back after cleaning the surface with alcohol. Skin tests are performed by an allergy specialist.

Blood tests (to measure IgE antibody levels) are widely available and can be done without an allergic specialist although the specialist is needed to interpret the results and advise management.

Apart from lactose intolerance and celiac disease, there are no diagnostic tests to diagnose food intolerance reliably. Miscellaneous tests:

How do you Treat Food Intolerance?

Intolerance to foods cannot be cured. The only way to treat food intolerance is by the following measures

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