Food and Asthma: Myths and Reality

A common question almost all patients ask from a physician is what they should eat and what they should not. Patients often have their own ideas and beliefs about what foods are good and which ones are not, for their disease. This information is obtained from their cultural and social environment, lay press and other media, and in modern times, from the internet.

Patient beliefs about Food and Asthma

Patients with bronchial asthma are very often concerned about the effect of the food that they eat on their condition. It is a very common observation that patients with asthma often avoid foodstuffs such as curd, banana and rice. A growing trend is to avoid “fast food” which is often the staple diet of many a young Indians now.  Parents of children who have asthma often do not let them have these food stuffs, and also milk and other milk products. Many types of fruits are also prohibited. Other than the so-called fast-food, such restrictions may be harmful as the diet can become unbalanced and several foods that give essential nutritional elements may be removed from the diet. This leads to malnutrition. In case of children, this can impair physical and mental development and also affect scholastic performance.

It is very important to sift facts from myths.

What is Food Allergy?

Certain foodstuffs may harm an asthmatic in a number of ways. Foods such as nuts, fish and sometimes lentils may cause an allergy. This is because the body produces certain substances, called IgE, that react with these foods. Sometimes, preservatives and coloring agents in foods can also cause allergy.  If an asthmatic who is allergic to these foods takes even a small quantity, he or she may have an increase in his symptoms due to aggravation of the disease.  This is different from food allergy causing gastrointestinal symptoms such as pain and diarrhoea. A large number of asthma patients believe they have food allergy.

How common is Food Allergy?

Studies have shown that true food allergy is present in only a small fraction of patients. It is quite uncommon. Out of 100 asthma patients who believe they have food allergy, less than 5% will actually be found to have true food allergy when tested in a laboratory. The rest only have a false belief. They are unnecessarily depriving themselves of many food items.

How is Food Allergy Confirmed?

The simplest but a very reliable way is the history of the patient – an evaluation of what the patient tells a physician. A patient may observe that his symptoms increase when he has a particular food and his asthma improves when he avoids it. One needs to be careful with such observations though. Firstly, the symptoms may have increased due to something else such as air pollution. Therefore, symptoms should increase every time a patient has these food stuffs, not that sometimes this happens and sometimes does not. However, identifying a particular food item as the culprit is not easy. We do not eat components of food separately. A meal consists of cereals, lentils, vegetables, fruits etc taken together and it is not easy even for a very intelligent patient to identify the specific food item causing an alleged allergy. However, the first clue will come from the history, correct or incorrect.

In a laboratory in a hospital, there are several ways to confirm allergy. Some methods are reliable and some are not. First, specific substances in blood that react with food components can be measured. These are called specifc IgE. However, studies have shown that mere presence of these substances in blood is no proof that food allergy is there. It is a pity that many patients stop so many food items after getting this very expensive test done. This test has very little clinical value and is not recommended.

Second, a skin test can be done with food item components. A sterile solution is made using the food components and injected into the superficial layers of skin. If the person is allergic, a pale reddish raised area of 5-10 mm is formed in the skin. However, this test is dangerous as it can produce severe reactions. It should be done only in a hospital where any emergency can be attended to. Again, like specific IgE, skin tests are also not reliable. A positive reaction does not mean the patient is allergic to the particular food item. This must be confirmed by another test as below.

The best method is to do a food challenge test. A small food portion is filled in a capsule so that the patient does not know which food is being tested. The person giving the capsule also does not know what it contains. Only a third person who filled the capsule knows which food is being tested. The lung function is measured using a test called spirometry that provides a measurement of our wind pipes or the airways. This is done  before taking the capsule and then about half an hour afterwards. If the patients is allergic, the lung function values will decrease after taking the capsule of food.

How can food allergy be treated?

There is no specific treatment for food allergy except that one stops consuming such food items. It is important that the drugs for asthma (the inhalers) be taken regularly as these  patients usually get asthma from other environmental and intrinsic factors too, even if they have a true food allergy.

It is not advisable to stop a particular food item in diet merely due to a suspicion. Most often, these beliefs and myths will turn out to be false. The patient must consult the physician and discuss the problem. Self-modification of diet can be harmful and lead to nutritional deficiencies.

To conclude, while it is true that a small number of asthma patients do have true food allergy and therefore should avoid such items in their diet, this is a very small number. Most of the asthmatics who somehow believe that they have food allergy will actually turn out not to have the allergy when tested in a laboratory. Food allergy should be confirmed only with reliable tests, recognizing that many available tests are of no value. Avoidance of food is recommended only after confirmation, and not on mere suspicion or false belief, so that diet balance is maintained and nutritional deficiencies are avoided. Treatment of asthma with prescribed inhalers must continue.