Asthma, a chronic inflammatory condition affecting the airways, is characterized by wheezing, breathlessness, chest tightness, and coughing. Recognized triggers include allergens, irritants, exercise, and emotional stress. Obesity is also considered a risk factor. While mainstream medical advice for asthma management doesn't traditionally emphasize diet, emerging research suggests a significant link between dietary choices and asthma development and symptom control. This article explores the growing body of evidence supporting the role of plant-based diets in both preventing and managing asthma.
The Emerging Evidence: Plant-Based Diets and Asthma
A recent review of published research indicates that increasing the consumption of fruits and vegetables while reducing dairy intake can help prevent asthma and alleviate its symptoms. This conclusion, though still debated, is supported by several studies examining the association between asthma and the consumption of various food groups.
Early Studies: A Glimpse of the Potential
One of the earliest studies, conducted in 1985, placed 35 asthma patients on a vegan diet for one year. The study, although lacking a control group, reported significant improvements in vital capacity and other clinical measures. This suggests that a vegan diet could potentially replace conventional medication.
A 2004 pilot study put 13 children with asthma on a diet free of milk and eggs, while nine others continued their usual diet. After eight weeks, peak expiratory flow rate improved by approximately 20% in the children who avoided milk and eggs, with no significant change in the control group. The weakness of this study was that it was not randomized: Parents chose whether to put their children on the special diet or continue giving them their normal diet.
More Recent Findings: Reinforcing the Connection
A 2015 study assessed the diet and health of 678 children in Puerto Rico. The study found that children who consumed the most dairy products were more likely to have asthma. This cross-sectional study, however, makes it difficult to differentiate between causes and effects.
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Benefits of Plant-Based Diets
A Mediterranean diet emphasizing plant-based foods has been associated with improved lung function, reduced asthma symptoms (such as wheezing), decreased asthma medication use, reduced asthma attack severity, and fewer hospital admissions due to asthma. Children born to women who consume a Mediterranean diet during pregnancy also have a lower risk of developing asthma symptoms. A study of Peruvian children found that fruits, vegetables, legumes, and cereals, along with reduced meat intake, lowered the odds of asthma risk.
Plant-based diets have demonstrated the ability to reduce systemic inflammation, a key factor in asthma exacerbation. These diets are also rich in fiber, which is positively associated with improved lung function. Fiber promotes a healthy gut microbiome, which plays a crucial role in immune responses and airway diseases.
Fruits and Vegetables: A Protective Effect
Eating fruits and vegetables may be especially beneficial for asthma. A meta-analysis of over 40 studies showed that high consumption of fruits and vegetables is linked to a decreased risk of asthma in children and adults. Fruits and vegetables have also been shown to improve lung function and make asthma severity and symptoms, including wheezing, more manageable
The antioxidants and flavonoids found in plant foods may have a protective effect by reducing inflammation in the body and airways. A study comparing a low antioxidant diet (less than one serving of fruit and two servings of vegetables) to a high antioxidant diet (five servings of vegetables and two servings of fruit per day) found that after 14 weeks, those who ate more fruits and vegetables had better lung function and a lower risk of asthma exacerbation.
Dangers of Dairy and High-Fat Foods
Studies indicate that dairy consumption can increase the risk of asthma and worsen symptoms. One study found that children who consumed the most dairy had higher odds of developing asthma. Another study showed that children with asthma who eliminated dairy and eggs for eight weeks experienced a 22% improvement in peak expiratory flow rate.
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High fat intake, consumption of saturated fat, and low fiber intake have all been associated with airway inflammation and worsened lung function in asthma patients. A study where participants with asthma reduced their saturated fat intake for 10 weeks experienced reduced airway inflammation. Whole food, plant-based diets are naturally lower in saturated fat.
The Role of Body Weight
Maintaining a healthy body weight can reduce the risk of asthma and help manage symptoms. Overweight and obese children are at higher risk of developing asthma, with the risk increasing as the degree of obesity increases. A study of elderly women found that both healthful and unhealthful plant-based diets were associated with a lower incidence of asthma symptoms over time, mediated by BMI.
Plant-Based Diets and Asthma: A Deeper Dive
Asthma in the Elderly
Asthma in the elderly is a phenotype of interest, especially in older women, where it tends to be more prevalent and more severe than in older men. Investigating the role of modifiable lifestyle factors such as diet for the primary prevention of this highly prevalent disease is warranted, especially among older women. Epidemiological studies on the effect of diet on asthma outcomes have widely focused on children and young to middle-aged adults.
Plant-Based Diet Indices and Asthma Symptoms
A study involving 5700 elderly women from the French Asthma-E3N study with dietary data in 1993 and 2005, assessed the incidence of asthma symptoms in 2018 among women with no asthma symptoms in 2011. The study evaluated a potential mediating role of body mass index (BMI) and the modifying effect of smoking.
The study found that both healthful and unhealthful plant-based diets were associated with a lower incidence of asthma symptoms over time, mediated by BMI. Associations with both healthful and unhealthful PDIs were mediated by changes in BMI by 33% and 89%, respectively.
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Plant-Based Diets and the Gut Microbiome
A high-fat diet modifies the composition of the gut microbiota, more specifically causes the reduction of protective bacteria, the expansion and colonization of invasive bacteria, and the reduction of SCFA concentrations, implying a potential role in inflammation and the immune response. These changes in microbiota could play an additional role in obesity-related asthma through changes in the production of bacterial-derived or modified metabolites, e.g., lowering the production of SCFAs that can induce anti-inflammatory effects
Inflammation and Oxidative Stress
Levels of inflammation, oxidative stress, and exposure to advanced glycation end products all contribute to the development of an asthmatic response and can be reduced with a plant-based diet.
Population-based studies showed a correlation between increased levels of serum high sensitivity-CRP (hs-CRP) with a high frequency of airway hyper-responsiveness and low forced expiratory volume in one second (FEV1) among asthmatics without heart disease. A plant-based diet has been shown to reduce markers of inflammation such as hs-CRP.
Studies have indicated that oxidative stress also plays an important role in the development of asthma. Airway oxidative stress also has been associated with declining disease status, poor lung function, and epigenetic changes. A plant-based diet protects against chronic oxidative-stress-related diseases. Dietary plants contain variable chemical families and amounts of antioxidants. Plant antioxidants may contribute to the beneficial health effects of dietary plant foods.
Dietary advanced glycation end products (AGEs) are highly oxidant, proinflammatory compounds, with highest levels present in cooked meats. AGEs are ligands for the AGE receptor (RAGE), a pattern recognition and danger signal receptor, with highest expression in the lungs, and an important driving force behind downstream Th-2 inflammation.
The Western Diet and Asthma
The Western diet, prevalent in developed countries, is dominated by convenience and highly processed foods, resulting in high intakes of refined grains, processed and red meats, desserts and sweets, fried foods, and high fat dairy products, with low intake of fruits and vegetables. In one study, higher cured meat intake increased the risk of worsening asthma symptoms over time by 76%, through a direct effect and to a lesser extent an effect mediated by BMI.
An epidemiological study comparing vegetarian women to nonvegetarian women found that nonvegetarian women had a 24% increased risk of asthma. Several studies have found that the Mediterranean diet had a protective effect against asthma.
Asthma Phenotypes and Endotypes
Asthma has different phenotypes and endotypes. Consequently, there are variations in its clinical severity and treatment response, and these differences may reflect their pathobiological pathways. Patients may respond very differently to the same therapeutic interventions despite having similar clinical symptoms. A long-standing clinical approach to asthma has been to categorize patients into phenotypes based on observable combinations of biological, clinical, and physiological characteristics. However, the strategy to link molecular mechanisms to specific phenotypes has been evolving.
Practical Implications and Recommendations
The existing research suggests that dietary interventions, particularly plant-based diets, hold promise for both preventing and managing asthma. A plant-based diet should be prescribed for all asthma patients. Medications used to treat the asthma patient may need to be titrated down as the treatment effects of a plant-based diet become evident. When treating patients with common comorbidities such as type II diabetes or coronary artery disease, medications specifically for these conditions will also need to be titrated as the treatment effects on these comorbidities become evident. For instance, plant-based diet is more efficacious in treating type 2 diabetes and as efficacious as Lovastatin in treating hypercholesterolemia.
A Stepwise Approach to Asthma Treatment
Asthma treatment is based on a stepwise approach. The management of the patient is control-based; that is, it involves an iterative cycle of assessment (symptoms, risk factors, etc.), adjustment of treatment (i.e. pharmacological, non-pharmacological and treatment of modifiable risk factors) and review of the response (symptoms, side effects, exacerbations, etc.).
The Importance of a Holistic Approach
It is important to continue to work closely with your health care provider to monitor your health and manage your asthma medications, even as you make dietary changes.