Post-Migration Changes in Dietary Patterns and Physical Activity among Adult Foreign Residents in Niigata Prefecture, Japan: A Mixed-Methods Study

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.


Introduction
Migrants are considered a vulnerable population group for nutrition-and lifestylerelated chronic diseases due to the shift in diet patterns and lifestyle with the change in the environment [1]. Previous studies have reported a higher body mass index and waist circumference in European Asians compared to counterparts with similar cultural and genetic backgrounds in their country of origin [2][3][4]. Significantly high prevalence rates of diabetes among ethnic minority groups from Turkey, Vietnam, Sri Lanka, and Pakistan compared to Norwegians [5] and among British South Asians than in the indigenous population have also been reported [6]. The process by which migrants adopt the dietary practices of the host country is referred to as 'dietary acculturation' and can be influenced by a variety of demographic, economic, social, and cultural factors [7]. Dietary acculturation is not linear but rather a complex, dynamic, and multidimensional process where immigrants retain or find new ways to use foods from their home country (from here on referred to as traditional foods), exclude traditional foods, and/or adopt the diet of the host country [8]. Satia-Abouta et al. [8] proposed that complex and dynamic relationships of socioeconomic,

Sample Characteristics
In total, 128 survey responses were received, and the socio-demographic characteristics of the respondents are presented in Table 1. The total sample consisted of 54 (42%) male and 74 (58%) female participants. The mean age of the participants was 32.6 (8.4), ranging from 18 to 68 years. The majority of the participants were from Asia (see Table S1.1 for representation from each country) and were students (n = 85). Most participants were unmarried, living alone, and had a monthly income of 100,000-200,000 ¥. About 42% of participants were married or living together, and among them, 35 (68.6%) had a partner of the same nationality, while the partner was a Japanese national in 14 (27.5%) of them. The mean length of residency in Japan was 5 years (SD-6.3, range = 0.5-40 years). Most respondents had no particular dietary habits and ate traditional foods at least once a week (63.3%). There were no significant associations between the frequency of traditional food consumption and demographic factors. While a significant association was found between the absence of particular dietary habits/restrictions and the lower frequency (<4 times a week) of traditional food intake (χ 2 (1, N = 128) = 5.222, p = 0.022), traditional dishes were consumed more frequently (≥4 times a week) by those with restricted beef intake (χ 2 (1, N = 128) = 7.991, p = 0.007; see Table S1.2). In general, fluency in the Japanese language was very poor to moderate ( Figure 1). Table 1. Socio-demographic characteristics of the survey and interview participants 1 .

Interview (N = 21)
Age, mean (SD) 32. 6  A total of 21 interviews were conducted, and the characteristics of the interview participants are summarized in Table 1. Interviewees ranged in age from 24 to 55, while the majority were female and university students, with a monthly income of 100,000-200,000 ¥. Two of the interviewees were married to a Japanese national. Many interviewees noted that they were consuming traditional foods occasionally or rarely.

Self-Reported Changes in Consumption of Foods/Food Groups
About 47% (n = 60) of the respondents reported changes in portion size after coming to Japan; among them, 58% (n = 35) mentioned that they eat much less than in their home country. Table 2 summarizes the list of foods with more than 50% of total change (eat much less or more compared to their home country). More than half of the respondents reported an increased consumption of noodles, raw fish, seaweed, seafood, green tea, soy sauce, and miso and reduced intake of fruits (See Table S1.3 for the detailed food list). A statistically significant relationship was found between low fruit consumption and low monthly income ( 2 (1, N = 128) = 25.467, p = 0.002; See Table S1.4).

Self-Reported Changes in Consumption of Foods/Food Groups
About 47% (n = 60) of the respondents reported changes in portion size after coming to Japan; among them, 58% (n = 35) mentioned that they eat much less than in their home country. Table 2 summarizes the list of foods with more than 50% of total change (eat much less or more compared to their home country). More than half of the respondents reported an increased consumption of noodles, raw fish, seaweed, seafood, green tea, soy sauce, and miso and reduced intake of fruits (See Table S1.3 for the detailed food list). A statistically significant relationship was found between low fruit consumption and low monthly income (χ 2 (1, N = 128) = 25.467, p = 0.002; See Table S1.4).

Self-Reported Changes in Food Preparation Methods and Dietary Behaviors
Food preparation methods and dietary behaviors for which more than 50% of respondents noted some sort of change are presented in Table 3 (see Table S1.5 for the detailed list). Increased practices of microwaving (76.5%) and using frozen foods (64.7%) were more prominent among students (see Table S1.6).

Factors Associated with the Procurement and Preparation of Traditional Foods
About half of the respondents reported that the availability of traditional food ingredients and restaurants is limited, while about 75% mentioned the higher prices of ingredients ( Table 4). The availability of traditional food ingredients was associated with the higher frequency of traditional food consumption (χ 2 (1, N = 128) = 4.001, p = 0.045; see Table S1.7). Online orders within Japan and international shops were the most common methods of purchasing traditional ingredients. The other methods of procuring traditional food ingredients noted by respondents were driving to international shops in other prefectures and asking friends who visit the home country to bring them.

Perceived Changes in Physical Activity
Nearly 73% reported changes in PA levels since immigration, while 55 (43%) mentioned increased PA levels. These changes were more evident in terms of walking, stair climbing, household chores, and cycling (Table 5). One hundred and four (81.3%), fifteen (11.7%), and nine (7.0) respondents described their lifestyle pattern as mostly standing or sitting, mostly walking or stair climbing, and heavy work, respectively.

Factors Influencing Post-Migration Dietary Changes: Qualitative Analysis
The thematic analysis of qualitative data identified 10 themes (factors) belonging to three categories (environmental, individual, and socio-cultural). Sub-themes were identified for each factor with regard to how and why dietary changes occurred. These factors and sub-themes are reported below with illustrative quotes (selected illustrative quotes for each sub-theme are summarized in Table S2.1). Thematic maps of qualitative findings are reported in Supplementary File S3. Figure S1 illustrates the thematic map of the environmental factors influencing postmigration dietary changes.

Environmental Factors
Affordability of Foods and Ingredients This factor consists of two sub-themes: (1) higher or lower prices of foods/meals and (2) adaptive purchasing and dietary behaviors. Many participants found that the cost of certain foods, mainly fruits, vegetables, meats, and traditional spices, are high compared to their home countries, while some Japanese foods like natto (fermented soybeans), tofu, etc., are more affordable to incorporate into their diet. The higher prices have made participants change their dietary behaviors by opting for cheaper foods, buying smaller quantities, or when the prices are lower. The cost of eating outside has led the participants to prepare their own meals, which they did not carry out back in their home countries.
The duration of stay in Japan and employment status shapes purchasing behavior. Recent immigrants tend to compare the prices between the host country and their home country when buying food and ingredients.
"I just think that everything is more expensive because I got here several months before. Fruits and vegetables here are very expensive. So, when I buy something, I still compare it with the Rupiah (Indonesian Currency)." (Interview #12, Female, Indonesia) Further, the purchasing and dietary practices adopted upon arrival in Japan can become a habit even though the circumstances change later.
"I eat a lot of chicken here in Japan but not a lot of meat. I mean, like beef. I think it is because of the price. Because first, when I came here, I was just a student. So, at that moment, I saw that the meat was very expensive. Now, I am working and I can afford it, but maybe it became some kind of habit for me." (Interview #13, Female, Kazakhstan)

Availability and Accessibility of Foods and Ingredients
This theme is composed of the following sub-themes: (1) a limited/wide availability or accessibility of foods or ingredients, and (2) adaptive purchasing and dietary behaviors. Participants expressed that while some ingredients/foods are less or not available (traditional spices, vegetarian food, halal food, and foreign food restaurants), some are difficult to procure in the same quantities (beef) or qualities as in their country of origin (traditional flavors). Difficulties in accessing traditional foods and ingredients were also discussed by many participants. On the other hand, participants reported that some foods and ingredients are widely available (tofu, mushrooms, and frozen foods) and easily accessible (convenience stores and bakeshops) in Japan compared to their home countries.
In response to the limited availability and accessibility, immigrants have adopted measures such as finding products that can be used as substitutions for traditional ingredients, fusing Japanese and traditional cuisines, ignoring the non-availability of ingredients that do not affect the flavor of traditional dishes significantly, and giving up the preparation of some traditional dishes. Due to the lack of stores or restaurants in Niigata that cater to the international community, immigrants have adopted measures such as driving to other cities where international stores are available, ordering online, or acquiring the skills to prepare and cook traditional/international dishes independently.
The duration of stay in Japan and fluency with the host language affect the accessibility of food.
"After a lot of searching when I first got here, I found the places where I could buy what I needed in Niigata. Like I know exactly where to go if I want pure ground beef rather than mixed pork and beef. There are certain places that sell that. So, when I am preparing local dishes sometimes, I have to get out on the car and go to about 4 to 5 different places to find everything I need. But I know exactly where to go now." (Interview #5, Male, USA) "I try to learn some Japanese foods, but my main problem is the language. I mean, when I go to the supermarket, I cannot distinguish well the ingredients. For example, if I find a recipe in English on the internet for Japanese food, I am like, 'ahh, okay,' and then I go to the supermarket, and it is difficult for me to find some things. For example, for soy sauce, there are different varieties. So, I cannot understand which one I need." (Interview #1, Female, Chile)

Food Safety and Related Information
Participants discussed (1) the perceived safety/unsafety of foods and ingredients in Japan compared to their home countries and (2) the lack of food-related information or knowledge. In contrast to the participants who described foods in Japan as safe and clean, some expressed their fear of buying products or preparing foods unavailable in their home countries due to a lack of related information or knowledge.

Climate in Niigata
The cold weather in the Niigata prefecture was mentioned as a factor that affected the changes in food intake (an increased rice amount and drinking tea and coffee) and food preparation methods by some participants.
"The weather in Japan, it is very cold for me. The region I live in Indonesia is quite hot, and it's a tropical country. I think it is easy for me to get hungry here, and I want to eat rice more than I'm in Indonesia. Also, it is so cold in my apartment, so I have to cook something easy and quick, so I just fry it." (Interview #17, Female, Indonesia) 3.6.2. Individual Factors Figure S2 illustrates the thematic map of the individual factors influencing postmigration dietary changes.

Family Structure/Living Status
The sub-themes include (1) the burden of preparing complicated or time-consuming meals for one person, (2) Japanese-foreign households, (3) the newfound responsibility of procuring and preparing foods, and (4) changes in meal-associated family traditions. While those who were living alone felt that preparing a full-course meal or time-consuming meal is a burden, the dietary habits of those with a Japanese spouse/partner reflected the two cultures (traditional foods of the foreign resident and Japanese-style meals).
"I got divorced recently, but when we were living together, we did do the whole, make the broth for two and half hours and do the soup. I don't have that kind of time right now. When cooking for people, I do a little bit more special, but for myself, no need of it." (Interview #10, Female, Russia) Some participants found themselves in a situation where they have to bear the responsibility of procuring and preparing food post-migration. Some interviewees mentioned that they no longer follow certain meal-associated family traditions in Japan, such as tea time.

Food Preferences and Limitations
The sub-themes of (1) preference for traditional foods/tastes, (2) newfound preference for Japanese foods/tastes, (3) willingness to try new foods, (4) ingrained habits and beliefs, and (5) health-related factors were identified under this theme. Interviewees express their preference for traditional foods/tastes in terms of missing traditional foods, avoiding Japanese products with flavors different from traditional products, and choosing foods with similar tastes or qualities to traditional foods.
"I prefer Chinese food because it's quite similar to Indonesian food. So, I prefer to go to Chinese restaurants than Japanese restaurants." (Interview #17, Female, Indonesia) According to participants' narrations, the newfound preference for Japanese foods/tastes and willingness to try new foods were catalysts for embracing Japanese foods, which led to an increased intake of Japanese foods, preparation of Japanese foods by themselves, and fusion of traditional and Japanese cuisines.
"I like to explore a lot, and I like to be creative, so sometimes I try to cook something, kinda Mexican style but with Japanese ingredients, I like to try some new stuff, and there are no restrictions. Zero." (Interview #18, Male, Mexico) Ingrained habits and beliefs and health-related factors influenced the post-migration diet changes by limiting or increasing the intake of some Japanese foods, while some immigrants described that their dietary habits are quite similar to those of their home country.

Post-Migration Lifestyle
Time restrictions and a busy lifestyle came up as factors of post-migration dietary changes, especially among students. A lack of time resulted in opting for simple foods that do not require much preparation time, bulk food preparation and storing, choosing foods that do not spoil quickly, missing meals (especially breakfast), or a fusion of traditional and Japanese cuisines.
"I am having Russian style, like lots of vegetable soups, but the bases and broth. . .it's like Miso because I don't have a lot of time to make the broth, I'm just like, Miso is fine. It's a kind of combing of foods." (Interview #10, Female, Russia) In addition, the difference between pre-and post-migration lifestyles has led some participants to start preparing and procuring food on their own. Figure S3 illustrates the thematic map of the socio-cultural factors influencing postmigration dietary changes.

Contrast between Traditional and Japanese Food Cultures
The sub-themes identified were (1) the influence of the characteristic features, (2) the positive effects, and (3) the problems of the Japanese food culture. According to the narrations of interviewees, they have incorporated characteristic features of the Japanese food culture into their post-migration diet, such as raw fish and a variety of root vegetables, tea with meals, and one-bowl meals in contrast to set meals in traditional cuisines. Participants described positive features of the Japanese food culture, including light meals, fresh foods, and low temptations for unhealthy foods, compared to their traditional food culture. However, light meals have resulted in an increased meal frequency as getting hungrier is faster than with their traditional diets. A lack of vegan or vegetarian options, additives, and higher sodium and sugar contents emerged as problems associated with the Japanese food culture.
Notions regarding Japanese culture among other nationals have resulted in dietary changes even before moving to Japan.
"Actually, before coming to Japan, my professors [in India] used to say that if you go to Japan, you should be non-vegetarian. Because, when the professors [in Japan] offer some food, you should not say 'no.' It is like a. . .kind of disrespect. And then I started to eat non-vegetarian food, like 6 or 7 months before coming to Japan." (Interview #2, Male, India) Relationships with Japanese People Some participants described how having close connections with Japanese people broadened their view of authentic Japanese foods and provided opportunities to explore and learn about Japanese cuisines. Further, Japanese language proficiency shapes the relationships with locals.
"Since I use a lot of Japanese in daily life, I have a lot of opportunities to get along with Japanese in general, like connect deeply. And a lot of elders share some secrets or give us some food. So, I think for me, the language opened a lot of doors and a lot of opportunities to try new stuff and get to know a lot of things." (Interview #18, Male, Mexico) Participants also highlighted how the COVID-19 pandemic impacted their relationships with locals and their diet behavior subsequently.

Religious Influence
Interview narrations revealed the influence of religion on the post-migration diet, which resulted in limiting eating out, checking the ingredients of foods before purchasing, and preparing their own meals.

Factors Influencing Changes in PA since Migration: Qualitative Analysis
Factors influencing PA changes were weather, post-migration lifestyle, and characteristics of Japanese culture. These factors and sub-themes are reported with selected illustrative quotes in Table S2.2. Figure S4 illustrates the thematic map of the factors influencing post-migration PA changes. The cold winter in the study area limits going out and engaging in PA or opting for indoor PA, while certain characteristics of Japanese culture, such as a health-conscious lifestyle (being in good shape, riding bicycles, and jogging), small apartment rooms, and perceived safety, drives PA behaviors. Although most participants expressed that they are walking more compared to their home country, some participants reported that changes in their PA are situational and not Japan-specific. "There's a change in physical activity, more physical activity in general. I did start and also stop doing various sports while here [in Japan] as a means of meeting people. So, more physical activity because I am going to places. Even if I lived in another country, this is the same, and this is not something Japan-specific. But I would say riding a bicycle is a Japan-specific thing, and starting sports is not Japan-specific, it's just a way of meeting people and having a community without too much effort. I got a car last year, so the physical activity kind of dropped, especially in this kind of weather." (Interview #10, Female, Russia) Table 6 summarizes how and why the post-migration changes and adaptive behaviors occurred.

Discussion
This study sought to explore the post-migration changes in dietary patterns and PA levels of foreign residents living in Niigata prefecture, Japan, and the factors affecting such changes. To our knowledge, this study presents the first insight into diet and PA changes among migrants in Japan without limiting them to a nationality or a region. The findings of this study will add to the scarce body of evidence on immigrant health in Japan. The survey respondents perceived an increased consumption of foods associated with the Japanese traditional diet and the use of frozen and microwavable food, and the decreased consumption of fruit. According to participants' narratives, different factors influence their eating behavior and PA, which can be environmental (availability, accessibility, and affordability of foods; food safety and a lack of food-related information or knowledge; and climate), individual (living status; post-migration lifestyle; and food preferences and limitations), or socio-cultural (cultural differences; relationships with Japanese people; and religious influences). Certain factors related to immigration and settlement, such as the duration of stay and Japanese language proficiency emerged as factors that shape dietary changes. Factors associated with PA changes were weather, post-migration lifestyle, and characteristics of the host culture.
During adaptation to Japanese food culture, an increased consumption of certain feature foods and ingredients in Japanese cuisines, such as noodles, raw fish, seaweed, seafood, green tea, soy sauce, and miso, is more evident. A recent study conducted in South Korea has reported an increased consumption of vegetables, kimchi, rice, and fisheries' produce, which are common in the Korean food culture, among Central Asian migrant workers [12]. The dietary changes of migrants from different regions are inconsistent owing to the different food cultures in each part. For instance, all the participants from the Americas reported that they are eating more noodles in Japan compared to their home countries, while there was no significant change in the noodle intake of many respondents from East Asia (Table S1.8). Noodle-based cuisines are readily available in Japan as prepackaged meals in supermarkets and convenience stores in addition to local restaurants and food stalls. Further, cup noodles are quite popular as a cheap and easyto-make meal. According to interview narrations, the preparation of noodle dishes was simple compared to other Japanese food. For instance, one participant mentioned, "I sometimes cook some Japanese food like 'yaki soba' or 'yaki udon' (fried noodles), something simple like that. Not complicated." (Interview #14, Female, Türkiye) Niigata prefecture is located along the coast of the Sea of Japan and is well-known for its fresh marine produce. The interview participants from land-locked countries and regions described that seafood is fresh, more affordable, and accessible in Niigata prefecture. Most participants from South and Southeast Asia reported an increased consumption of green tea, as black tea culture is common in these regions (Table S1.9). An increased use of frozen and microwavable foods was observed, attributing to the larger representation of international students in the study sample. Interview narrations further revealed that the availability and easy accessibility of frozen foods also affected the increased consumption. Due to the abundance of fresh produce throughout the year and negative public perception, frozen and chilled foods' usage is limited in South and Southeast Asian countries (Table S1.4).
Satia et al. [8] described the cumulative effect of sociodemographic and cultural factors, changes in diet-related environmental and psycho-social factors, and the level of exposure to the host culture on the dietary intake of immigrants. Our findings are also consistent with a previous study, which reported the availability, accessibility, and affordability of dietary products, and time management, as key determinants of change in dietary behaviors [21] among Australian residents of Sub-Saharan African ancestry. A lack of family support, reduced access to traditional food ingredients, and curiosity regarding new foods in the host country were found as determinants of the dietary changes among recent Chinese migrants in Australia [22]. Many interviewees discussed that imported ingredients or products from their home countries are considerably costlier due to import taxes or limited availability. In addition to the high cost or less availability, they highlighted the lack of diversity in fruits, vegetables, and certain meats in Japan compared to their home countries. The cross-sectional study results align with these findings, as most respondents reported a limited availability and high cost of traditional food products as well as a reduced intake of fruits. Survey results further showed an association between monthly income and fruit intake. Particularly, a reduced intake of fruits and vegetables is of concern as it is a risk factor for chronic diseases [23]. The combined effect of living alone and a busy lifestyle on reduced fruit and vegetable consumption also emerged as they opt for foods that do not perish quickly and do not require going to the market frequently. Due to the interplay between the availability, affordability, and accessibility of food ingredients, the migrants are inclined to explore cheaper or widely available alternatives and omit or substitute the ingredients in traditional food recipes [24].
The changes in family structures influenced post-migration eating behavior. Most of the participants in the current study were foreign students who were living alone. The interview narrations revealed that most students lived with their families before moving to Japan, and they were not solely responsible for their diet. Therefore, the newfound responsibility to purchase and prepare food on their own, combined with time restrictions, has made the participants opt for more convenient and affordable options. Characteristics of the study area emerged as the factors affecting the dietary changes. For instance, the climate of Niigata prefecture is characterized by long cold winters with heavy snowfall and strong winds, which is different from the climate of the southern parts of Japan. Further, interviewees narrated that while foreign food restaurants and shops that offer international food are limited in Niigata prefecture, those are widely available in large metropolitan areas with a high immigrant density, such as Tokyo. Therefore, they have found ways to procure traditional ingredients by ordering through online shops or driving to shops in other prefectures. Previous studies have also reported that urban areas with a high proportion of immigrants had better access to ethnic foods and stores that cater to their food preferences [25,26]. Those who described themselves as 'food explorers' with the willingness to try new foods endorsed the Japanese food culture by incorporating many readily available and affordable Japanese foods, such as tofu, natto (fermented soybeans), miso, etc., into their regular diet or mixing the Japanese and traditional ingredients to modify the ethnic recipes. Survey findings of the current study showed that the frequency of traditional food consumption is associated with individual dietary habits and the availability of traditional ingredients. Previous studies have reported that accessibility and individual food preferences affect the overall well-being or satisfaction of migrants in their new environment [26].
As highlighted by the interview narrations, the duration of stay and Japanese language proficiency shape dietary changes. As the duration of their stay increases, immigrants are exposed to mainstream food culture and become more open to trying local foods and adapting to the local diet [8]. In addition, longer stays provide opportunities for a deeper exploration of food markets and methods to procure traditional ingredients, which can lead to adopting bicultural eating habits. The relation between changes in dietary habits and the length of stay in the host county was reported in previous studies [8,27,28]. Language proficiency provides migrants the opportunities to form deeper connections with the locals. Such relationships help gain insight into Japanese cuisines, ingredients, and authentic tastes [8,26]. The use of English to communicate is limited among local residents in Japan, who can introduce migrants to local dishes and ingredients, local food establishments that may not be easily accessible to migrants, and cultural food practices, such as seasonal eating and dining customs. A good command of the language also facilitates reading labels and understanding nutritional information, effectively communicating food preferences and restrictions to local vendors and restaurants, and asking questions about ingredients, cooking methods, etc., which can be important for making food choices. Therefore, fluency in the Japanese language plays a crucial role in accessing and understanding local food culture and enables the migrants to make informed choices about their diet.
Japanese locals are known for their health-conscious and relatively active lifestyle. According to the Global Health Observatory figures in 2016, 65% of adult Japanese people met the recommended level of PA by the World Health Organization [29]. Interview narrations of the current study suggested that the physical and cultural environment in Japan is supportive of PA and acts as a catalyst for increased PA levels. In particular, Niigata prefecture has a PA-supportive physical environment equipped with jogging, bicycle, and skiing trails, leisure parks, mountains, and surfing spots. The culture in Japan values staying active, sports, and engaging in outdoor recreation, which in combination with perceived safety, might encourage migrants to be physically active. Some interviewees acknowledged that increased PA levels are not specifically due to the Japanese influence but rather global trends. The majority of the immigrants in the current study described their daily life as 'mostly sitting and standing,' and were engaged in some form of unstructured PA (walking, climbing stairs, and cycling) rather than regular sports. These findings are likely to be associated with the composition of the survey population, which consisted of 65% of international students. In spite of the PA-supportive environment in Niigata prefecture, its climate was recognized as a barrier to outdoor PA. A recent study conducted in Norway described the changes in PA habits among Italian immigrants. They reported a perceived increase in PA levels after moving to Norway and that Italian immigrants in Norway are more physically active than their counterparts in Italy [30].

Strengths and Limitations
A key strength of this study was the mixed-method approach, which combined the qualitative data to contextualize the quantitative results. Another strength was the diversity in the sample population, which consisted of participants from different regions of the world and socio-demographic backgrounds. However, caution should be taken when generalizing the findings of this study to all migrants in Japan, as the characteristics of the study area were also influencing factors. In addition, the extent and nature of postmigration changes can vary with the country of origin and time of migration. Further, changes in diet and PA may have already started before migration in the country of origin due to nutrition transition. As such, post-migration changes among individuals from the same country or ethnic group could be at different levels. Therefore, we are unable to make direct and general comparisons between cultures. Furthermore, interviews were conducted by one researcher via a method the participants felt comfortable with. The fact that the interviewer is a foreign national in Japan allowed the participants to express their opinions freely without any reservations and facilitated a better interpretation of the participants' comments by the researcher.
The study also has some limitations, mainly in relation to the generalizability of the findings, as described in the previous paragraph. The sample size of the quantitative study was small but thought to be representative of the study population as it consists of foreign residents from different parts of the world and socio-economic backgrounds. However, a small number of participants from some regions of the world limits our ability to draw conclusions based on the cultural and regional differences of immigrants. In addition, a higher proportion of the study sample was students whose dietary behaviors are generally known to be different from the dietary habits of other adults, and it might have introduced statistical bias. Further, the study used self-report measures to collect information that may have introduced recall and/or social desirability bias. However, the questionnaire was pre-tested and anonymously administered to minimize the chances of reporting bias. Another limitation of the study was the use of an online questionnaire, which may introduce response bias by favoring those who are frequent online users. However, migrants are a hard-to-reach population; thus, an online questionnaire provides a convenient way to reach them.

Implications for Practice and Future Research
The findings of this study shed light on important health-related behaviors among an immigrant population in Japan and can be used to inform initiatives to promote health in this rapidly growing community. For instance, health promotion and education interventions can be initiated to introduce immigrants to the local food culture and easy-to-make recipes, ways to access traditional foods and ingredients as well as health-related information, and understanding food labels and nutritional information.
Despite the limitations, the current study has the potential of expanding the research on the acculturation process and health consequences. Further, studies that aim to better understand and compare the post-migration dietary and PA changes among immigrants from different metropolitan, urban, and semi-urban regions within the country can inform stakeholders and policy makers to develop national-level support programs for newly arriving migrants.

Conclusions
In conclusion, findings from this study support the notion that changes in diet and PA have occurred among migrants in Niigata prefecture, Japan. The post-migration dietary changes are characterized by the increased intake of foods attached to Japanese cultural identity and frozen and microwavable food, and a reduced consumption of fruits. The changes in dietary behaviors and PA were mainly driven by environmental, individual, and socio-cultural factors. While our findings are in agreement with the model proposed by Satia et al. [8], qualitative data highlight the influence of study area characteristics, the duration of stay, and fluency in the Japanese language on the post-migration dietary and PA changes in the current population. The findings of this study provide a better understanding of how and why post-migration changes occur, which can help plan and implement appropriate interventions for foreign residents in Japan.

Institutional Review Board Statement:
The study was conducted in accordance with the Declaration of Helsinki and approved by the Ethics Committee of Niigata University, Japan (No. 2022-0005).

Informed Consent Statement:
Informed consent was obtained from all subjects involved in the study.

Data Availability Statement:
The data used and/or analyzed during the current study are available from the corresponding author upon reasonable request. The qualitative data are not publicly available due to ethical considerations.