Breath of Fresh Air: Feature Articles

Chapter 20: Diet and Your Asthma

Asthma is a chronic illness with symptoms that come and go. Who with asthma has not wondered whether the cough or wheeze or chest tightness that he/she is experiencing might have been brought on by something that he/she ate? In the same line of reasoning, one wonders whether by eating a special diet — or by taking special vitamins or minerals — one might be able to improve one's asthma, or even cure it.

In addition, scientists have observed recent trends in asthma — it appears that asthma is becoming more common and for some groups more severe than in past years — and they do not yet have a satisfactory explanation for these changes. Some scientists have wondered whether changes in our diet might account for at least some of these differences over time in asthma. What do we know about asthma and its relation to the food we eat?

Can changes in your diet help your asthma?

…or can national trends in our diet explain recent increases in the frequency and severity of asthma?

As one might predict, lots of folklore and "popular wisdom" precede scientific knowledge on this subject. In his book, Treatise on Asthma, the famous medieval physician, Maimonides, wrote several chapters on diet therapy for asthma. One of his recommendations is the much renowned "chicken soup," which is now thought to be good for just about any illness! Ask patients with asthma about their own experiences (as was done in a questionnaire survey in Melbourne, Australia), and one finds that most patients have tried to change their diet in one way or another to help their asthma. Common preparations added to the diet (as reported in this study) included calcium supplements, vitamin C, multivitamins, fish oil supplements, primrose oil, and herbal remedies. Commonly avoided food items included nuts, milk and chocolate (dairy products), sausages/frankfurters, pickled onions/gherkins, and fruit cake. Also reported to cause asthmatic symptoms were food additives (for example, monosodium glutamate [MSG] and sulfites), red wine, and flavored toothpaste.

Many people with asthma try adding or avoiding certain foods or additives to help their breathing.

The relationship between what we eat (involving thousands of different chemicals with each meal) and asthmatic reactions in our bronchial tubes is undoubtedly complex and difficult to sort out. One way to test for food sensitivity in persons with asthma is called a "double-blind" method. On one occasion the person is given the food to which he or she is thought possibly to be sensitive; on another occasion an inactive food substance is given. On both occasions the food is disguised, so that neither the person with asthma nor the investigator performing the test knows whether the real food or the inert substitute is being eaten. The subject is tested for an asthmatic reaction on both occasions. When experiments of this sort are conducted, very few persons with asthma (only about 2-4 out of 100) actually have asthmatic reactions to the suspected offending food.

One might also try to evaluate a suspected food allergy by blood testing, looking for the allergic type of antibody (called immunoglobulin E) circulating in the blood and targeted at that particular food. However, the test is imperfect: sometimes it is absent even when a food allergy exists, and sometimes it is present when no allergy is experienced. Also, even when present in the blood, the nature of the allergic reaction is not specified. True food allergies more often cause intestinal upset (such as nausea, vomiting, and abdominal cramping) or areas of swelling (for example, of the lips or tongue or back of the throat) than they cause narrowing of the bronchial tubes (that is, asthmatic reactions). Blood test results cannot distinguish the likelihood of one type of reaction compared to another type.

Blood tests are generally unreliable for predicting asthmatic reactions to foods.

Often, then, you are left to decide on your own whether a food or food additive causes your asthma to worsen. You need to become a scientist and to conduct your own experiments -- with you as the subject of the experiment. If you have a peak flow meter at home, you can be very precise in your experimentation. If you suspect that you have a sensitivity to something that you eat, measure your peak flow before and after eating it to see whether your lung function gets worse after eating. Do the same experiment at another meal, when you don't eat the food to which you might be sensitive. Did the breathing (and peak flow) get worse one time and not the next? Can you do the experiment again, and get the same results? If the answer is yes and you are convinced that you have a food sensitivity, then you should carefully avoid the food to which you are sensitive. This approach is likely to help you more than any general recommendation about your diet that you receive from a doctor, relative, friend, or local health "expert."

You need to be your own scientist – and research subject – to discover your own food sensitivities.

Trends in the frequency of asthma among various populations have indicated that our environment plays a significant role in the development of asthma. One striking observation has been that racially similar groups of people who move from rural to urban environments and who adopt more Western styles of living typically develop more asthma than those who do not move. Although adopting our Western culture may mean many different things (think of sleeping on mattresses with dust mites and spending more time indoors exposed to other potential allergens), one difference is certainly eating a Western diet. In the same way, is it possible that over the past 20 years our dietary changes, as a society, have contributed to making asthma more common in this country?

Cultural changes can influence the development of asthma, but how much of an effect does diet have?

The answer at the present time appears to be an uncertain "maybe." No one knows for certain if dietary changes are to some degree making asthma more common, and if they are, which changes in the diet might be responsible. Different doctors have their own theories. Some believe that our diets contain too much salt or too much of certain fatty acids (omega-6 fatty acids such as linoleic acid); others believe that we lack enough magnesium, antioxidants (for example, vitamins C and E), and certain other fatty acids (omega-3 fatty acids such as eicosapentanoic acid found, for instance, in dark meat fish). In the Nurses' Health Study conducted by investigators affiliated with Brigham and Women's Hospital, more than 75,000 adult women completed dietary questionnaires and were evaluated for their risk of developing asthma over a period of 10 years. No food group or vitamin was found to have a definite relationship with their likelihood of developing asthma.

We are left with the possibility that trends in our diets may influence how common or severe asthma has become in our society, but without knowledge as to which aspects of our diets might be helpful and which might be harmful. No one can honestly advise you what to eat in order to make your asthma better. An "asthma diet" remains only someone's guess or, worse, hope for profit. For the present time, we are best off avoiding those foods that, by personal observation, we know make us worse and following the advice of Maimonides from 800 years ago when he suggested that: "Moderation in food type is the key to keeping the bronchioles open."

In the Nurses’ Health Study of more than 75,000 women, no food group or vitamin had a definite relationship to their development of asthma.