In the present study, DASH dietary pattern could decrease odds of obesity in both urban and suburb area. In the best of our knowledge, this is the first study evaluated the relationship of DASH diet and obesity in both urban and suburb region of Iranian adults as a Middle Eastern country. In line with our findings, Tabibian and colleagues showed that more adherence of the DASH diet could reduce the odds of obesity in women . Also, findings of another study showed more adherence of Chinese adults to the DASH diet is associated with lower odds of obesity . A randomized clinical trial conducted on overweight and obese women with polycystic ovary syndrome showed that following of DASH diet is accompanied by reducing in weight and BMI significantly . Moreover, in one meta-analysis  as well as some other studies [17, 20, 23, 33-36], the results showed that more adherence of DASH diet can significantly reduce the odds of obesity. However, in the present study adherence to the DASH diet has no significant effect on central obesity in suburb area, unlike in urban area. To addressing the causes of this discrepancy, it may be mentioned that behavioral factors affecting obesity in rural and suburb areas, divided into downstream and upstream. Low levels of education and low SES are upstream factors . Poor diet and lifestyle among the rural and suburb population are downstream factors affecting obesity in these areas [38, 39]. Recent study showed residents of Shahedieh as a suburb region have different diet quality and lifestyle in comparison of the urban region . In suburb region, some dairy products such as milk, cheese, and yogurt as prominent component of DASH diet are traditionally made from local cows which have more fat than pasteurized and commercial packed samples commonly consumed in urban area. Moreover, data confirmed that the lack of medical and primary prevention services, long distance to obtain medical care and reduced welfare facilities (i.e. recreations centers, supermarkets) in these areas are further causes [41-43]. Also, no significant relationship was observed between adherence of this dietary pattern and abdominal obesity in the study of Gharabi et al. . Similarly, in another study, no significant relation was observed between adherence to the DASH diet and weight loss . In addition, in the study of Wong et al., no significant effect was seen between compliance of this dietary pattern and BMI .
The mechanisms and beneficial effects of the DASH diet on obesity have not yet been fully elucidated. However; this dietary pattern could exert its beneficial effects on obesity due to the high intake of fruits and vegetables, and whole grains which contain large amounts of antioxidants, magnesium, fiber and potassium [44-47] . Also, fruits, vegetables, and whole grains containing both soluble and un-soluble fiber  could reduce obesity through several mechanisms, including appetite control, food intake regulation , and increasing chewing time . Soluble fibers also absorb more water, creating a viscosity gel and increasing gastric distance . In addition, fiber by providing low energy and slowing gastric emptying could provide a feeling of satiety and reduce serum insulin secretion . Fermentation of fiber could reduce hunger and appetite through modifying eating pattern of human intestine by producing short-chain fatty acids, releasing intestinal peptides and hormones such as cholecystokinin and glucagon-like peptide 1[54-56]. Phytochemicals are bioactive compounds found in fruits and vegetables, which include compounds such as polyphenols and their derivatives, carotenoids and thiosulfates, which could reduce obesity by modifying the human intestinal microbiota . In addition, dairy intake is high in this diet and some previous studies investigating beneficial effects of dairy products on weight loss [57, 58] and reduced prevalence of central obesity [59, 60] in adults. The underlying mechanisms of dairy products related to obesity is its effects on improving energy and fat balance , fat absorption , appetite or metabolic activity of intestinal microbiota [63, 64]. Also, high levels of calcium in dairy products could be effective in weight loss / body fat [25, 47, 65, 66]. Calcium exerts its anti-obesity role through mechanisms such as regulating adipogenesis, inhibiting lipogenesis and increasing lipolysis in fat metabolism, regulating proliferation and apoptosis of fat cells, increasing thermogenesis, increasing secretion and decreasing fat absorption, and modulating intestinal microbiota . DASH diet is rich in foods such as vegetables, fruits, nuts, legumes, and whole grains, which are containing high amount of polyphenols. High intake of such foods reduces obesity . Foods rich in polyphenols are effective on obesity through various mechanisms including the effect of prebiotics on intestinal microbiota, decreased appetite, increased energy consumption by inducing thermogenesis, increasing lipolysis, and stimulation of fat cell apoptosis . Also, legumes in this diet are valuable food group which due to low energy density, could replace high-energy foods that are important in the prevention and management of obesity . In the DASH diet, red meat intake is low. Red meats increase the odds of gaining weight and obesity, because they are rich in saturated fatty acids, cholesterol, sodium and nitrate [70, 71] and are classified as high energy density foods . Also in this dietary pattern, low intake of sweetened beverages, due to their high sugar content, could reduce the odds of obesity [73, 74]. Because these products are a source of liquid sugar, they feel less saturated than solid sources . In addition, sodium intake is low in the DASH diet, a meta-analysis have shown that consuming more sodium is associated with an increased odds of obesity . The reason could be mentioned for this relationship is that higher sodium intake causes thirst and more fluid. Salty foods are often high in fat and energy, and that these foods are enjoyable and motivate people to consume higher amounts of these kinds of foods .
4.1 Strengths and Limitations
Regarding this study's strengths, to the best of our knowledge, this was the first research on the relationship of DASH dietary pattern with obesity was performed on a large sample size of Iranian adults that covered both urban and suburb area. Furthermore, administration of a validated semi-quantitative FFQ to collect the study data by a face-to-face interview using trained interviewers ensured the data accuracy. Third, with regard to the reliability, a wide range of potential confounders were adjusted in this study.
Considering this study limitations, the following can be mentioned: in this cross-sectional study, the causal relationship between DASH diet and obesity could not be assessed. Consequently, further prospective studies are required in this area. Second, although a valid food frequency questionnaire was used, but there was a measurement error and an error in the classification of people participating in the study. Moreover, we cannot reject the possibility of residual confounding bias, since unknown or unmeasured confounders may exist that affected our results. Finally, our participants with odds of obesity might have been advised to reduce their fat intake, which led them to alter their dietary habits. However, such possibility cannot be resolved in a cross-sectional study.