Q: Is there a diet for asthma? Can certain foods help prevent symptoms?
The role diet plays in preventing and managing chronic diseases such as cardiovascular disease and type 2 diabetes is undisputed.
Mounting evidence also suggests that eating a healthy diet can help ease symptoms of asthma, a chronic condition affecting 11 per cent of Canadians.
And the most protective foods to help you breathe easier, it seems, are no farther away than your refrigerator.
Asthma occurs when the airways (bronchial tubes) become inflamed and narrow, causing chest tightness, wheezing, coughing, mucus production and difficulty breathing. There is no cure for asthma; medications are needed to treat and prevent symptoms.
Asthma attacks range from mild to severe and are usually provoked by environmental allergens (e.g., dust mites, mould, pollen, pet dander) and food allergens. Other triggers include cold weather, exercise, stress, viral infections, cigarette smoke, chemical fumes and scented products.
Risk factors for asthma include a family history of asthma, having certain allergies that affect the eyes and nose, workplace exposure to dust and fumes, and obesity.
How diet can make a difference
Asthma rates have been on the rise since the 1980s and diet may be partly to blame. As a Western eating pattern has become more prevalent, so has asthma.
High in refined grains, processed and red meats and added sugars, a Western diet has been associated with airway inflammation and worsened lung function in people with asthma.
In contrast, a Mediterranean diet, plentiful in fruits, vegetables, whole grains, seafood and healthy fats, is linked to a lower risk of asthma and better-controlled asthma in children.
Antioxidant nutrients (e.g., vitamins C and E) and phytochemicals (e.g., beta-carotene, flavonoids) in plant foods are thought to reduce inflammation by neutralizing harmful free radicals in the lungs.
Fibre in plant foods also feeds beneficial gut bacteria, which then produce compounds that can dampen inflammation.
What to eat
There is no specific “asthma diet,” but research suggests the following foods and nutrients support lung function and may help minimize the frequency and severity of asthma symptoms.
Fruits and vegetables. Many studies have tied a high intake of fruits and vegetables to a lower risk of asthma and improved asthma control in children and adults. In adults, for example, eating at least five vegetable servings and two servings of fruit each day, especially citrus fruit, is associated with fewer asthma attacks.
Include fruits and vegetables high in vitamin C, a nutrient linked to improved lung function in people with asthma. Oranges, grapefruit, kiwifruit, strawberries, mango, cantaloupe, red and green bell peppers, broccoli, cauliflower, Brussels sprouts and cabbage are good sources.
Lycopene-rich foods, such as tomato juice and tomato sauce (both high in vitamin C), may also help lessen the severity of asthma attacks.
Vitamin E-rich foods. This antioxidant nutrient may help reduce asthma symptoms, as well as lower the risk of developing asthma.
Excellent sources include wheat germ oil, sunflower seeds, sunflower oil, safflower oil, grapeseed oil, almonds, hazelnuts, peanuts and peanut butter.
Vitamin D. Low vitamin D levels have been associated with a higher risk of asthma and a greater severity of asthma attacks.
Health Canada recommends 600 international units (IU) per of vitamin D day for children aged 1 to adults aged 70, and 800 IU daily for adults over 70.
Very few foods contain vitamin D naturally; salmon is one of the best sources (350 to 715 IU per three ounces). Milk and fortified non-dairy milks also supply vitamin D (100 IU per one cup).
In general, a daily vitamin D supplement of 1,000 to 2,000 IU can help Canadian adults maintain a sufficient blood level. Your doctor can check your vitamin D level and advise on supplementation.
Fish. Studies suggest that introducing fish early in life (six to nine months) and eating it at least once a week may reduce asthma and wheeze in children up to four-and-a-half years old, while fatty fish may be beneficial for older children.
Omega-3 fats in salmon, trout, sardines and mackerel may help reduce airway inflammation. Fish also supplies selenium, a mineral that acts as an antioxidant.
Leslie Beck, a Toronto-based private practice dietitian, is director of food and nutrition at Medcan. Follow her on Twitter @LeslieBeckRD
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