March 11, 2019
THE NUTRITIONAL STUDIES
Looking at the studies, there is a paucity of evidence that the DASH diet has any effect on asthma prevalence or morbidity because it has not been studied other than a pilot study in poorly controlled asthma that showed a non-statistically significant reduction in symptom scores.(Ma et. al. 2013) The known benefits to cardiovascular disease are not immediately translatable to asthma.
The Mediterranean diet is the most studied of all of the "positive", i.e. thought to be beneficial diets. When it comes to the onset and prevalence of asthma, the Mediterranean diet has mixed results. It has positive results in relation to asthma morbidity.(Barros et. al. 2008)(Sexton et. al. 2013)(Garcia-Marcos et. al. 2013)(Papamichael M. 2017)
Other studies that looked just at vegetable and fruit intake noted improved asthma symptoms with increased intake. (Garcia-Larsen et. al. 2016)(Wood et. al. 2012)(Guilleminault et. al. 2017)(Appel et. al. 2008) Finally, the infamous Western diet is believed to be associated with worsening asthma but this is not strongly supported by the studies. (Brigham et. al. 2015)
The best summary of the available data as it relates to macro diets and asthma is that increasing intake of vegetables and fruits in the diet has strong evidence for benefit.
Hypothetically, but not proven, it is likely that the Western diet is not beneficial and the DASH and Mediterranean diets are beneficial. The lack of data on the western diet and asthma does not take away from the known mechanistic pathways of this diet inducing inflammation and immune dysregulation that could affect an asthmatic patient.
Knowing that the nutritional studies are incomplete as they relate to asthma specifically, let's attack this issue of diet and asthma from another angle, inflammation. The available best quality nutritional data is that what decreases total body inflammation and excess weight gain will decrease the disease burden whether it is cardiac, pulmonary or gastroenterological disease.(David et. al. 2014)(Sharon et. al. 2014)(Pollan 2013)(Manco et. al. 2010) Interestingly, obese individuals have a 92% increased risk of asthma. (Kull et. al. 2006) Therefore, one would presume that what drives obesity may also drive asthma morbidity. Is there a surrogate population that has a rapid change in weight and also asthma disease?
The obese population that undergoes bariatric surgery is this group. They undergo a rapid metabolic change that is a perfect surrogate for a dietary change. Post bariatric surgery patient outcomes note that asthma steroid medicine needs drop post-surgery by 40%. (Reddy et. al. 2011) The reason at first blush was thought to be related to decrease caloric intake and straight weight loss. However, a deeper dive at the pathophysiology of gastric bypass has proven that the surgically induced shift in the microbiome's bacterial makeup and subsequent inflammatory response is at the root of disease improvement. (Rubino F 2017)(Celiker H 2017) This microbiome shift can also be achieved by dramatically changing the diet. (Conlon et. al. 2015)(Carmody et. al. 2015)(Kau et. al. 2011)(Sonnenburg et. al. 2016)(Turnbaugh et. al. 2009)(Cani P 2008)
This may be the key to understanding how diet and asthma are linked since the epidemiological data is moderate to weak. The emerging strong evidence that the microbiome drives inflammation and disease morbidity is critical in making decisions where they are related to nutrition. Now we must continue to follow the data as it evolves in regards to what dietary influences have the most profound positive effect on the intestinal microbiome and thus inflammation, endotoxemia and asthma.
The story continues next week,
Ma Contemp Clinical Trials Article
Barros Allergy Article
Sexton Journal of Asthma Article
Papamichael Public Health Nutrition Article
Garcia-Larsen Allergy Article
Wood J Clinical Nutrition Article
Guilleminault Nutrients Article
Appel Circulation Article
Brigham Annals Allergy Asthma Immun Article
David Nature Article
Sharon Cell Metabolism Article
Pollan NYT Article
Manco Endocrine Reviews Article
Kill Allergy Article
Reddy Obesity Surgery Article
Rubino Scientific American Article
Celiker Medical Hypothesis Article
Conlon Nutrients Article
Carmody Cell Host Microbe Article
Kau Nature Article
Sonnenburg Nature Article
Turnbaugh Science Trans Medicine Article
Cani Diabetes Article