It is not news that eating a balanced diet helps to maintain our overall health. But for asthma patients, the benefits are even more pronounced.

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Different dietary patterns have positive or negative effects on the risk of developing asthma, control of symptoms and exacerbations, and lung function deterioration.

Diet and airway inflammation

Chronic inflammation of the airways is characteristic of asthma. High saturated fat and low fiber intake have been associated with increased airway inflammation (neutrophilic and eosinophilic). Conversely, fruit and vegetables (good sources of fiber and antioxidants) appear to lower airway inflammation.

The Western diet generally contains large amounts of refined grains, red meat, processed and fast foods, sugar, and dairy products. This diet is pro-inflammatory due to a lack antioxidants (which increase susceptibility to oxidative stress) and high levels of saturated fats (which stimulate the innate immune system).

Some forms of asthma also prolong activation of the immune system. Ongoing systemic inflammation leads to enhanced inflammation of the airways, an increased rate of exacerbations and worsening lung function.

In contrast, the typical Mediterranean diet (consisting of large amounts of fruit, vegetables, wholegrains and seafood) contains many anti-inflammatory nutrients, including unsaturated fatty acids and antioxidants.

Beneficial foods:

• Antioxidants, such as vitamins A, C and E, reduce the lung inflammation that results from cellular damage by free radicals. Sources: fruit and vegetables.
• Vitamin D reduces the risk of patients developing more severe asthma. Sources: milk, eggs, fish, and sunshine.
• Omega-3 fatty acids may help to reduce asthma symptoms. Sources: cold-water fish, nuts, seeds

Foods to avoid:

• Saturated fat leads to increased immune-activated airway inflammation. Sources: fast food, dairy products
• Sulfites (preservatives) and sodium can trigger asthma symptoms. Sources: wine, dried fruit, pickles, shrimp, and salt

Diet and the gut microbiome

The bacteria in the gut ferment fiber, which produces metabolites, such as short-chain fatty acids. These molecules can modify the immune response, which has downstream effects on airway inflammation and sensitivity in animals with allergic airways disease.

Diets rich in fiber can modify the composition of microbial species in the colon and create an environment that is more protective against allergic airway responses. A high-fat diet also alters the balance of gut microbiota.

In contrast, however, it increases the number of invasive bacteria, reduces the levels of protective bacteria and short-chain fatty acids, and subsequently increases the risk of inflammation. The effects of these changes on asthmatic immune responses is not known.

Asthma and food allergies

Food allergies are a much greater risk in asthma sufferers. When the immune system detects a food allergen, it releases histamine, which causes the symptoms of an allergic reaction. It can also trigger asthma-like symptoms, such as wheezing, coughing and breathing difficulties, and may lead to a life-threatening asthma attack. Therefore it is important that asthma patients avoid any foods to which they are allergic.

Asthma and obesity

The asthmatic population has higher rates of obesity. Being overweight can lead to poorer disease outcomes, such as decreased control, and increased exacerbations and medication use. Therefore, eating a healthy diet may be beneficial for asthma patients not only by the direct effects of particular food groups, but also by helping with weight loss.

Multidisciplinary disease management

There is a growing awareness around the effects of diet on the development and control of asthma. Understanding how different foods can affect their symptoms can help asthma patients make beneficial choices to improve their health.

A higher intake of fruit and vegetables appears to have the most positive dietary impact on the development and control of asthma. A multidisciplinary approach that includes a healthy diet and physical activity is a promising strategy for disease management, as well as prevention.