In current study, we have investigated the connection between two major dietary patterns and presence of allergic disorders. Adherence to a Western pattern typified by high intake of snacks, nuts, dairy products, tea, fast foods, and chicken was related with a higher risk of AR after adjustment for measured confounders.
Although contributory, genetic risk factors alone cannot account for the increasing prevalence of atopy [27]. Diet has been implicated as one of the environmental factors contributing to the pathogenesis of this diseases [28, 29]. Epidemiological studies of atopy have focused mainly on relationships with individual intakes and evidences have been inconsistent. An advantage of analysis of whole profile of a diet is that individuals do not eat single foods, but meals, which constitute a dietary pattern. Furthermore, methodological challenges was existed in which consuming of dietary ingredients are increasingly correlated, and chance results may derive from indiscriminate multiple statistical analysis. Actually the cumulative effects of numerous dietary components in a dietary pattern may be more closely show real nutritional or dietary information in a population, and possibly can be translated easily into public health policies [20].
Modern diets routinely include more processed and synthetic foods with increased amounts of fats and refined carbohydrates with decreased values of fiber, fruits and vegetables versus more traditional diets. These alterations have been affected gut microbiome, metabolic reactions and immune activity which all of the may involve in lengthy low-grade inflammation and disturbance of homeostasis and eventually higher risk of atopy [30]. At present in Westernized countries, intake of fruit, vegetables, whole grains and fish is generally low, and intake of fast foods, sweets and snacks is high which are containing a high amount of saturated fats, sugar and salt and poor in fiber and antioxidants. In our study, the Western dietary pattern has the greatest score for snacks, nuts, dairy products and fast foods.
AR is a widespread health challenge influencing many individuals from childhood to adulthood [31]. It is described through nasal itch, rhinorrhoea, sneezing, and nasal congestion [32, 33]. Rhinitis with watery and mucous rhinorrhoea may be happens post eating hot, spicy nutrition and autonomic induction via neuropsychosomatic factors related with food ingestion may be regard for non-immunological rhinitis [34]. Inflammatory and allergic form of rhinitis are considered as multi-factorial disorders, and environmental elements such as diet, are potentially contribute in the etiology [35, 36].
Our results demonstrate that the odds ratio of having AR was 2.5 times more for individuals in the highest versus those at the lowest tertile of the Western dietary pattern. The relationship between allergic rhinitis and habitual dietary habits has been evaluated in a few investigations [37–40]. Associations of AR with fatty acids, high fatty acids foods [37–40], fruit, and antioxidants [39, 40] were evaluated, but findings were conflicting. Along with our findings, in a cross-sectional study of 10 years old children in Taiwan, factor analysis showed that children have high-protein, high-fat, Western diet had a remarkably 1.1 more odds of having AR (95% CI:1.01–1.2). Additionally, children without AR were found to have a lower intakes of fruits, dairy products and meat compared to children with AR [41]. In another study, frequent intake of fast foods was related with AR (OR = 1.5; 95% CI:1.1-2.0) in school children of Mexico [42].
A Western dietary pattern often includes high pro-inflammatory and low-antioxidant food items, which could affect responsiveness to environmental stimuli. Omega-6 fatty acids were existed in greater amounts in fast foods and processed foods in the Western dietary pattern convert to arachidonic acid, which switches to inflammatory mediators, i.e. leukotrienes and prostaglandins [16]. For instance, prostaglandin E2 inhibits T-helper cell type 1 (Th1) and enhances the Th2 phenotype, which is prominently found in allergic condition [16]. Moreover, low levels of antioxidants cannot prohibit the activation of nuclear factor-κB (NF-κB) by higher levels of reactive oxygen species (ROS) [43], thus inducing the innate immune reactions via cytokine production and devastation of cellular elements such as DNA, and proteins [44].
Many investigations have reported that the consuming of antioxidants rich foods (i.e., fruits and vegetables) protect from allergic conditions [45], whereas others reported a positive [46] or null relationship [45, 47]. We could not detect any relationship between the risk of atopy and consumption of fruits and vegetables across the tertiles of Western dietary pattern.
Dietary consumption of red meats, eggs, green vegetables, legumes and see foods, total fat, saturated fatty acids, fiber, riboflavin, thiamin, carotene, phosphorous, iron, zinc, selenium and folic acid were significantly decreased across tertiles of Western pattern and so inversely related with prevalence of AR. In a study performed on 1002 Japanese pregnant females, no measurable association was observed between intake of meat, eggs, total fat, saturated and monounsaturated fatty acids, and cholesterol or the ratio of n-3:n-6 PUFA and AR [48].
Previous studies have highlighted the allergenic properties of nuts in AR which is confirmed our finding [37, 49]. In a study performed among children, more consumption of nuts was associated with a more than two-times risk of AR [37].
Although asthma, eczema, and AR are associated to allergic immune reactions, the first 2 disorders did not represent any association with the studied dietary patterns. Lower prevalence of asthma and eczema in our study population which causes a smaller samples size might be a reason for lack of association. Consistent with our findings, in a review on 10 observational studies among North American, European, and Asian countries did not revealed any relationship between a Western dietary pattern and incidence or prevalence of asthma [50].
Traditional dietary pattern, which had a more factor loadings for vegetables, organs meat, potato, vegetable oils, eggs, and whole grains was not significantly related with any risk of allergy in our study. Consistently, in a prospective primary school children cohort, dietary pattern rich in meat, seafood, fruits, vegetables, cereals, rice and eggs, was not connected with any risk of rhinitis [51].
Adjustment for energy intake is a standard protocol in nutritional epidemiology for standardization of food and nutrient intake regarding to total food intake. Although most epidemiological surveys on dietary patterns and respiratory manifestations did not adjust for energy intake. Moreover, we collected data on potential confounders, including age, BMI and WHR and adjusted for them in the multivariate regression analysis to remove confounding as a probable explanation for the results.
In spite of careful evaluation of our study population, current research has several limitations. First, the cross-sectional nature of study does not allow determining the causal association and second, the correlation of dietary patterns with asthma and eczema is based on relatively small cases and might just be a spurious result.