Background Obesity is one of the most important public health problems in the world, which is occurred by various factors. The purpose of this study is to explore the causes of obesity in the Kurdish regions of Iran with a qualitative approach. Methods A qualitative content analysis study was conducted in the Kurdish regions of Iran from June 2019 to November 2019. The data were collected by holding focus group discussions and semi-structured interviews with 111 obese and thin men and women, and experts from different fields, who were selected through purposive sampling. Additionally, the data were analyzed by the conventional content analysis approach following the steps proposed by Graneheim and Lundman. The researchers used ATLAS.ti (Version 2019) software for data analysis and management. Lincoln and Guba’s criteria were used to assess the quality of the research. Results The results of the data analysis were classified into 5 categories and 16 sub-categories. The main categories included the modern lifestyle, sociocultural norms, indigenous culture of nutrition, lack of institutionalization of exercise, and low health literacy. Conclusion Changing people's beliefs and values about obesity and thinness, changing the dietary habits of individuals, expanding and institutionalizing exercise and physical activity, and enhancing health literacy can prevent and control obesity.