Certain conditions such as obesity & gastro-oesophageal reflux disease are risk factors that can increase the likelihood of asthma in susceptible patients (Brown et al., 2012). These conditions are caused by diet and therefore diet already plays a role in having asthma. It is also a known fact that oxidative stress and airway inflammation are central features in the manifestation of asthma which may be caused by the lack of antioxidants and key nutrients (Garcia-Larsen et al., 2016). Current evidence suggests that antioxidant vitamins C and E and a higher intake of fresh vegetables and fruits might have a protective effect on asthma.

Malnutrition has been shown to lead to immune dysfunction and impaired immunocompetence which then in turn increases the bodies’ vulnerability to illness and infections (Julia, Macia & Dombrowicz, 2015). States of malnutrition result from consuming a diet in which nutrients are either lacking or excessive. The hormones leptin, cytokines interleukin-6 and tumor necrosis factor-a associated with obesity have been found at similar elevation levels in both obese and asthmatic patients which suggests a link between the two (Wendell, Baffi & Holguin, 2014).

Various research models have confirmed that obesity exacerbates allergic asthma and that the observed effects are not solely dependent upon TH2 cell responses. IL-17A-producing lymphoid cells are required for the increased basal antigen-independent airway hyperactivity that is induced by a high-fat diet or by genetic obesity (Rance & O’Laughlen, 2011). Furthermore, high fat meals have been shown to cause an increase in airway neutrophilia which causes impaired bronchodilator recovery in obese patients with asthma (Suskind, R. M. 2013). 

Malnutrition, specifically obesity, is an independent predisposal factor for atopy, a heightened immune response to allergens suggesting additional asthma indicators (Wendell, Baffi & Holguin, 2014). The connection between asthma and obesity is through the impairment that an excess of adipose tissue causes to the body’s ability to adequately respire (Suskind, R. M. 2013). In extension to this introduction of a normocaloric diet without any dietary restrictions shows a marked improvement in asthmatic symptoms for obese children and adolescents diagnosed with asthma and restrictive calorie diets have shown to improve the same for adults (Luna-Pech et al., 2014)

While there has been evidence to suggest that obesity is factor is asthma and diet causes obesity there has been little substantiated evidence to suggest that any dietary factor substantially influences change (Silveira & et al., 2015). 

It has been suggested that oxidants and antioxidants may play a role in the alleviation of asthma symptoms. The theory is that dietary antioxidant acts on the epithelial lining of the lungs, and may reduce oxidative damage; this reduction of oxidative damage results in reducing bronchoconstriction and inflammation in asthma patients (Wood et al., 2012). From a systematic review of the evidence for the efficacy of vitamin C supplementation in the treatment of asthma, it was concluded that there were no significant effects and that the evidence was insufficient (Milan, Hart, & Wikinson, 2013). Other studies involving the use of vitamin C and E supplements in patients with mild asthma also concluded that there was no significant benefit to users (Misso & Thompson, 2013). 

The strongest argument so far for both symptom alleviation and improvement in quality of life amongst asthmatic patients are the DASH diet and the Mediterranean diet.  The DASH and Mediterranean diet are both characterized by high consumption of vegetables with a moderate consumption of protein as well as low consumption of saturated fatty acids from animal sources. These diets however have two key marked differences; the Mediterranean diet promotes consumption of high monounsaturated fatty acids from olive oil as well as the regular consumption of red wine (Ma & et al., 2013). Though there have not yet been any relevant studies regarding the efficacy of the DASH diet in asthma management there has been some supporting evidence for marked improvement of asthma symptoms when adherence to the Mediterranean diet is followed (Sexton & et al., 2013).

The promotion of these diets based on the slight supporting evidence would however be both unreasonable and unethical considering that these trials do not specify a set meal plan for either the Mediterranean or the DASH diet because they have not been well regulated. Any supporting evidence for either diet is therefore discredited due to a lack of parameters being set for the studies which causes all the data to henceforth be unreliable.

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