Asthma is a common chronic disorder. Its symptoms include uncomfortable breathing difficulties such as wheezing, coughing and chest tightness which can escalate to shortness of breath (intense tightening in the chest, difficulty breathing, breathlessness or a feeling of suffocation) and even death. Asthma is caused by inflammation and swelling in the bronchial tubes that carry air in and out of the lungs. In 2012, research in Canada ascertained that 22% of teenage males, 17% of teenage females and 10% of adults were suffering from asthma and its prevalence continues to increase every year. Worldwide, it is estimated that asthma accounts for one in every 250 deaths (1,2).
A recent large review, encompassing over 150 previous scientific studies, was published on March 13, 2020 by researchers from the Physicians Committee for Responsible Medicine. This review looked at associations between dietary factors and asthma risk as well as symptom control in children and adults and discovered that dietary choices may be a potent way to reduce the distress of asthma.
The following are their major findings (1).
Foods that influence the onset and severity of asthma
Fruits and Vegetables
High consumption of fruits and vegetables is associated both with reduced risk of developing asthma and fewer asthma symptoms in people of all ages.
Diets that emphasize fruits, vegetables, legumes and whole grains along with limiting meats and dairy products are associated with reduced risk of asthma and lower severity of symptoms
Consuming dairy products is associated with increased risk of asthma and worsening of asthma symptoms.
Typical diets eaten in the developed world emphasize consumption of animal products at the expense of fruits, vegetables, legumes and whole grains. These “Western” dietary patterns are associated with increased inflammation of the airways, worsening of lung function in asthmatics and increased asthma prevalence.
Potential mechanisms for the influence of foods on asthma
Plants naturally produce phytochemicals which protect them from a variety of pests and diseases. One important group of phytochemicals is the antioxidant group. Antioxidants derived from consuming plants may be reducing inflammation and improving lung function in asthmatics (1,3,4).
Oxidative stress occurs during normal metabolism of the human body. It is caused by the overabundance of free radicals, highly reactive and short-lived molecules produced naturally when oxygen is used to produce energy. Free radicals are missing an electron and will react with just about any other molecule they encounter to obtain another electron, thereby creating a new free radical and an ensuing cascade of new free radical production. These hyperactive molecules cause damage to DNA and other parts of human cells including those in the lungs. Antioxidants stabilize free radicals by donating one of their own electrons, halting free radical damage while maintaining their own equilibrium and not becoming another free radical in the process.
Antioxidants can be produced by the body but many of them are obtained through the diet. On average, plant-based foods contain 64 times more antioxidants than animal-based foods. In fact, the maximum amounts of antioxidants present in all animal foods tested is 100 mmol/100gm while that of plant foods goes up to 289,000 mmol/100 gm (5). Examples of some of these antioxidant phytochemicals are carotenoids (beta-carotene, lycopene and lutein), flavonoids, indoles and isoflavones.
You don’t need to go searching for a few food types that are at the top of the antioxidant-containing food list. Diets consisting of significant amounts of animal-based foods are antioxidant poor while eating mainly a variety of plant-based foods creates a diet that is antioxidant rich due to the thousands of bioactive antioxidant phytochemicals that can be found in plants.
Lung diseases are associated with inflammation in the gut. Higher consumption of dietary fiber can lower inflammation and improve lung function likely due to positive effects on the gut microbiome (1,6,7).
Fiber is the preferred food for the beneficial microorganisms that live within the gut microbiome. In turn, these microbes produce short-chain fatty acids such as butyrate that reduce the production of inflammatory cytokines, modulating metabolism and immune responses. Reduced inflammation in the gut signals for lower inflammation in the airways as well (1,8).
In addition, dietary fiber intake lowers the level of glucose in the blood which leads to lower production of inflammatory cytokines (1). It also increases the strength of the intestinal barrier, thus preventing proteins that might trigger an inflammatory immune response from entering the bloodstream (1,9).
Animal products contain no fiber. However, a plant-based diet is rich in fiber with the potential to lower airway inflammation.
Consumption of a single, high-fat meal increases levels of inflammatory compounds that influence inflammation of the airways. Studies suggest that saturated fatty acids are pro-inflammatory while unsaturated fatty acids inhibit the inflammatory response (1,10).
High fat diets might also increase inflammation through negative effects on gut bacteria. Low-fat vegan diets seem to improve asthmatic symptoms by not eliciting an inflammatory response (1).
Increases in n-6 polyunsaturated fatty acids (omega-6s) along with decreases in n-3 polyunsaturated fatty acids (omega-3s) are linked to increased inflammatory molecules and the worsening of asthma symptoms (1).
Being Overweight or Obese
Children who are overweight are at higher risk of developing asthma than children of normal weight. This risk rises as degree of obesity increases (1,11).
Higher body weight is associated with worse asthma control in both children and adolescents (1,12,13).
The increased inflammatory molecules released by adipose tissue (fat-storing tissue) may be the mechanism for this effect (1,14).
Weight loss in both children and adults with asthma result in improvements in lung function as well as better asthma control and higher quality of life.
Asthma patients show higher prevalence of vitamin D deficiency than people without asthma. Lack of vitamin D is also linked to more severe asthma symptoms (1). The mechanism for this effect is not clear and more research is needed.
Vitamin D is produced in humans by spending time outdoors with skin exposed to the sun. Alternatively, vitamin D supplements are inexpensive and efficient for keeping vitamin D levels up during winter months. Vitamin D can also be obtained through fortified plant-based milks.
Final Thoughts (1)
The researchers who performed this review conclude that “recommendations to increase fruit and vegetable consumption, while decreasing saturated fat and dairy intake, are supported by the current literature recommendations” for the prevention and treatment of asthma. Most people in the developed world do not meet the daily recommended intake of fruits and vegetables. Yet they exceed recommended levels of dietary fat.
Choosing a diet to improve asthma means emphasizing the consumption of fruits, vegetables, legumes and grains and reducing or eliminating animal products.
Finally, the researchers caution that many of the findings of this study are based on associations and interventional trials are necessary to confirm their results.
1 Alwarith, J., Kahleova, H., Crosby, L., Brooks, A., Brandon, L., Levin, S.M., Barnard, N.D. The Role of Nutrition in Asthma Prevention and Treatment. Nutrition Reviews. March 13, 2020; Vol. 0(0): 1-11. Doi:10.1093/nutrit/nuaa005
3 Hu, G., Cassano, P.A. Antioxidant Nutrients and Pulmonary Function: The Third National Health and Nutrition Examination Survey (NHANES III). Am J Epidemiol. 2000 May 15; 151(10): 975-981. Doi: 10.1093/oxfordjournals.aje.a010141.
4 Schünemann, H.J., Grant, B.J., Freudenheim, J.L., Muti, P. et al. The Relation of Serum Levels of Antioxidant Vitamins C and E, Retinol and Carotenoids With Pulmonary Function in the General Population. Am J Respir Crit Care Med. 2001 Apr; 163(5): 1246-1255. Doi:10.1164/ajrccm.163.5.2007135.
5 Carlsen, M.H., Halvorsen, B.L., Holte, K., Bøhn, S.K., Dragland, S., Sampson, L. et al. The total antioxidant content of more than 3100 foods, beverages, spices, herbs and supplements used worldwide. Nutr J. 2010 Jan 22; 9: 3.
6 Hanson, E., Lyden, E., Rennard, S., Mannino, D.M., Rutten, E.P.A. et al. The Relationship Between Dietary Fiber Intake and Lung Function in the National Health and Nutrition Examination Surveys. Ann Am Thorac Soc. 2016 May; 13(5): 643-650. Doi: 10.1513/AnnalsATS.201509-609OC.
7 Berthon, B.S., Macdonald-Wicks, L.K., Gibson, P.G., Wood, L.G. Investigation of the Association Between Dietary Intake, Disease Severity and Airway Inflammation in Asthma. Respirology. 2013 Apr; 18(3): 447-454. Doi: 10.1111/resp.12015.
8 Zhang, Z., Shi, L., Pang, W., Liu, W. et al. Dietary Fiber Intake Regulates Intestinal Microflora and Inhibits Ovalbumin-Induced Allergic Airway Inflammation in a Mouse Model. PLoS One. 2016 Feb 12; 11(2): e0147778. Doi: 10.1371/journal.pone.0147778. eCollection 2016.
9 Farshchi, M.K., Azad, F.J., Salari, R., Mirsadraee, M., Anushiravani, M. A Viewpoint on the Leaky Gut Syndrome to Treat Allergic Asthma: A Novel Opinion. J Evid Based Complementary Altern Med. 2017 Jul; 22(3): 378-380. Doi: 10.1177/2156587216682169.
10 Wood, L.G., Garg, M.L., Gibson, P.G. A High-Fat Challenge Increases Airway Inflammation and Impairs Bronchodilator Recovery in Asthma. J Allergy Clin Immunol. 2011 May; 127(5): 1133-1140. Doi:10.1016/j.jaci.2011.01.036. Epub 2011 Mar 5.
11 Black, M.H., Zhou, H., Takayanagi, M., Jacobsen, S.J, Koebnick, C. Increased Asthma Risk and Asthma-Related Health Care Complications Associated With Childhood Obesity. Am J Epidemiol. 2013 Oct 1; 178(7): 1120-1128. Doi: 10.1093/aje/kwt093. Epub 2013 Aug 6.
12 Borrell, L.N., Nguyen, E.A., Roth, L.A., Oh, S.S., Tcheurekdjian, H., Sen, S., et al. Childhood Obesity and Asthma Control in the GALA II and SAGE II Studies. Am J Respir Crit Care Med. 2013 Apr 1; 187(7): 697-702. Doi: 10.1164/rccm.201211-2116OC.
13 Denlinger, L.C., Phillips, B.R., Ramratnam, S., Ross, K., Bhakta, N.R., Cardet, J.C., Castro, M. et al. Inflammatory and Comorbid Features of Patients With Severe Asthma and Frequent Exacerbations. Am J Respir Crit Care Med. 2017 Feb 1; 195(3): 302-313. Doi: 10.1164/rccm.201602-0419OC.
14 Wood, L.G., Gibson, P.G. Dietary Factors Lead to Innate Immune Activation in Asthma. Pharmacol Ther. 2009 Jul; 123(1): 37-53. Doi: 10.1016/j.pharmthera.2009.03.015.