The migrant population of Japan is gradually increasing, but it is not well known how and why diet and physical activity (PA) change post-migration. Therefore, this study used a mixed-method approach to investigate the changes in dietary patterns and PA through a web- and paper-based survey (n = 128) and understand the contextual factors for those changes through semi-structured interviews (n = 21). Descriptive and thematic analyses of quantitative and qualitative data were conducted, respectively. The majority of survey (57.8%) and interview (66.7%) participants were female, and the mean duration of stay in Japan was 5 and 3.6 years, respectively. The survey revealed an increased consumption of foods attached to Japanese culture, frozen and microwavable food, and a reduced consumption of fruits. We identified environmental (availability, accessibility, and affordability of foods; food safety and diet-related information; and climate), individual (living status; post-migration lifestyle; and food preferences and limitations), or socio-cultural (relationships with Japanese people; cultural differences; and religious influences) factors that impact diet changes. Language proficiency and the duration of stay shape dietary behaviors. Determinants of PA changes were climate, lifestyle, and the influence of Japanese culture. In conclusion, immigrants in Japan experience post-migration diet and PA changes, and this study adds knowledge about how and why such changes occur.
Keywords: Japan; dietary patterns; immigrants; mixed-method research; physical activity; post-migration changes.