Childhood obesity has become the public health threat globally, and obesity is one of the two major causes of non-communicable diseases in China. Common epidemic obesity is an excessive accumulation of fat caused by a long-term imbalance between energy intake and consumption. In addition to the adverse effects on children's physical health, overweight and obesity have negative impacts on children’s mental health, resulting in depression, anxiety, poor interpersonal relationships and other mental problems. Although genetic and biological factors are critical factors affecting child overweight and obesity, researchers have realized that it is also urgent to explore possible impacts from the perspective of children's ecological environment. Based on research on Chinese samples and Bronfenbrenner's ecological theoretical perspective, the current literature review reorganized the research on the risk factors for childhood obesity from five ecological systems, including four environmental systems and one chronosystem.

Bronfenbrenner's ecosystem theory (1994) is one of the most widely used ecological theories in the field of human development. The ecosystem theory guides children's development and education researchers to view developing individuals as being settled in a nested and interactive environmental structure, while the environment directly or indirectly affects individual development in various ways. These nested and interacted systems include four environmental levels, including microsystem, mesosystem, exosystem and macrosystem. Meanwhile, the ecosystem theory also includes the timing factor, which is the chronosystem.

From the perspective of Bronfenbrenner's ecosystem theory model, this review is based on relevant literature sampling from urban and overseas Chinese, and summarizes the influencing factors of overweight and obesity in the four environmental levels of children's microsystem, mesosystem, exosystem and macrosystem and one chronosystem. The prevention and intervention of overweight and obesity in children provide systematic theoretical reference. It must be pointed out that this review cannot exhaust all possible factors, but try to sort out and summarize the factors that have been clearly related to Chinese children's overweight and obesity in existing studies.

Microsystem is the innermost layer of children's ecosystem, and also the most direct and interactive environment for children to participate in activities, including families, kindergartens and schools, peer groups and health service centers. In the microsystem, this review summarizes the existing research on family feeding, family sports and exercises, and teacher and peer effects. Mesosystem refers to the interaction between two microsystems, which has an impact on children’s physical health. This review reviews the coparenting between parents and grandparents, and the communication between parents and kindergartens or schools. Exosystem is an external system that children are not directly involved in, however, it has an indirect impact on their development. Mothers working full-time and the environment of their communities are reviewed, which may indirectly affect children's physical development through their families. Macrosystem is the cultural and social background embedded in microsystem, mesosystem and exosystem. The emphasis of Chinese culture on diet, the promulgation of the National Nutrition-related policy and the influence of electronic media advertising on children's physical development in the macrosystem are reviewed. Chronosystem is the timing factor, which encompasses change or consistency over time in children's environment. Family migration in the chronosystem is discussed.

From the perspective of ecosystem theory, the research on the influencing factors of childhood obesity and overweight in China is still immature. There are three main problems. First, according to the theory of ecosystem, there are more recommendations on child obesity prevention and intervention should be made, such as family-based intervention, school-based or school-family intervention, and community-family intervention. Second, there are still many factors to be explored, such as child influences on feeding and other parenting factors. The existing research is limited to examining single factors, or to a series of family demographic variables on child overweight and obesity and has not been fully explored from the perspective of the ecosystem in which children live. Third, the research designs are cross-sectional and only provide descriptive results, lacking long-term follow-up on revealing the mechanisms on how the related factors affect the associations between children’s diet or their exercise habits and body weight level. Also, measures are mainly adapted from Western countries or self-developed tools. There are few validated and universal tools to use.

The developing trend of overweight and obesity is not optimistic in our country. However, the majority of the study is not thorough and systematic. Guided by the ecological perspective, how to design and collect data to study the ecological influences is worthy considering and can guide us to prevent and intervene childhood obesity early on.