Food Insecurity and Major Diet-Related Morbidities in Migrating Children: A Systematic Review

Children of migrant families are known to be at a higher risk of diet-related morbidities due to complex variables including food insecurity, cultural and religious beliefs, and sociodemographic factors like ethnicity, socioeconomic status, and education. Several studies have assessed the presence of specific diseases related to dietary issues in migrant children. This systematic review aims to highlight the existing body of work on nutritional deficiencies in the specific vulnerable pediatric population of immigrants. Refugees were intentionally excluded because of fundamental differences between the two groups including the reasons for migration and health status at the time of arrival. A total of 29 papers were included and assessed for quality. Most of them described a strong correlation between obesity and migration. A high prevalence of stunting, early childhood caries, iron and vitamin D deficiency was also reported, but the studies were few and heterogeneous. Food insecurity and acculturation were found important social factors (nevertheless with inconclusive results) influencing dietary habits and contributing to the development of morbidities such as obesity and other metabolic disorders, which can cause progressive unsustainability of health systems. Public health screening for diet-related diseases in migrant children may be implemented. Educational programs to improve children’s diet and promote healthy-living behaviors as a form of socioeconomic investment for the health of the new generations may also be considered.


Introduction
During the course of history migratory patterns have been defined by demands for work, education, escape from armed conflict and poverty, or climate change [1,2]. In the recent past, high-income countries (HIC) have consistently received international migrants with steady increases over time. The estimated number of migrants to Europe and Northern America exceeded the number of emigrants by 25.9 million in the decade 2010-2020 [1,2]. This paper does not make reference to the political aspects of migration surrounding voluntary and involuntary migration (the forced displacement precluding asylum seekers and refugees), and aims to objectively provide the status of nutrition amongst children in migrant populations globally.
Food insecurity (FI) is a common problem among migrant people and entails several issues such as cultural and religious beliefs, socio-demographic, economic, and environmental factors, education, Global migration: The drivers of migration can be conceptualized into 5 categories: economic, social, political, demographic, and environmental factors, the former 2 perceived as having the greatest effect on the volume and patterns of migration [2]. Economic motives move migration both to developed countries and to developing countries with monetary interest. Migrants seeking work but opting to remain within their regions of origin, cross to adjacent countries to satisfy their economic interests. As well as these so-called push factors, migrants are pulled for recruited labor to satiate voids in the low and high-skilled workforce [34][35][36][37][38].
Migrant flow (international): The number of international migrants arriving in a country (immigrants) or the number of international migrants departing from a country (emigrants) over the course of a specific period [33].

Search Yields, Risk of Bias, and Quality of Reporting
The initial search identified 299 studies ( Figure 1). 29 studies were included in the final analysis after 270 papers were excluded on the basis of the inclusion/exclusion criteria. A detailed description of the selected articles, with study characteristics, is reported in Table 7. The quality assessment of the full text papers included in the present systematic review is reported in Table 8. Global migration: The drivers of migration can be conceptualized into 5 categories: economic, social, political, demographic, and environmental factors, the former 2 perceived as having the greatest effect on the volume and patterns of migration [2]. Economic motives move migration both to developed countries and to developing countries with monetary interest. Migrants seeking work but opting to remain within their regions of origin, cross to adjacent countries to satisfy their economic interests. As well as these so-called push factors, migrants are pulled for recruited labor to satiate voids in the low and high-skilled workforce [34][35][36][37][38].
Migrant flow (international): The number of international migrants arriving in a country (immigrants) or the number of international migrants departing from a country (emigrants) over the course of a specific period [33].

Search Yields, Risk of Bias, and Quality of Reporting
The initial search identified 299 studies ( Figure 1). 29 studies were included in the final analysis after 270 papers were excluded on the basis of the inclusion/exclusion criteria. A detailed description of the selected articles, with study characteristics, is reported in Table 1. The quality assessment of the full text papers included in the present systematic review is reported in Table 2.  [26]. HIC= high income countries.  [26]. HIC= high income countries.  Levels of acculturation negatively associated with overweight/obesity; children with urban-to-urban migrant caregivers more likely to be overweight/obese than those with rural-to-urban migrant caregivers 9,7% overweight/obese (> males, >11-13 yrs rather than 14-17 yrs, >urban-to-urban rather than rural-to-urban)  times more likely to be overweight/obese than those of more acculturated parents -more acculturated more likely to provide fruits daily or more but also more sugary snacks

3-8 year obesity
Parents' food insecurity in their childhood associated with obesity-promoting behaviors and outcomes 20% overweight/obese; parents with food insecurity in childhood: 1) evaluated their children weighing less than ideal 2) allowed more servings of soda and sweets; early life material deprivation: 1) less concern about children's diets, 2) less concern child eating too much or becoming overweight

Overweight, Obesity, and Associated Complications
Evidence for this outcome comes from 21 papers: 13 cross-sectional studies, 5 cohort studies, 3 randomized controlled trials. Quality was determined "good" for 18 of them, and only "fair" for 3 studies. Twelve studies were conducted in the USA, the rest were performed in Canada, Brazil, China, Australia, and several countries in Europe. The studies included different variables such as SES, acculturation, ethnicity, eating habits, lifestyles including physical activity and sleeping hours, thus making the studies extremely heterogeneous.
Many studies reported a high prevalence of overweight/obesity among immigrant children.
A binational study (Mexico and California, USA) performed on 603 mother-child dyads by Rosas et al. [35] found a significantly higher prevalence of obesity among the children of Mexican descent who were born in California compared to those who were born in Mexico (53.3% vs 14.9%; p < 0.01). Maternal obesity was a determinant of childhood obesity in both samples, but it was significantly higher in California (49%) compared to Mexico (33%; p < 0.01). Although the link between maternal obesity and child's weight status may suggest genetic or epigenetic factors, it probably also strongly reflects cultural and environmental characteristics shared with the child.
The paper of Kaiser et al. [36] examined the influence of age and gender on food patterns of Latino children in rural communities in California. 51% of the total sample was overweight or obese, with no significant effect of neither age nor gender on food patterns; mother' s acculturation level was positively related (p = 0.0002) to children consumption of less healthy foods. This contradicts the findings of Rosas on the basis of quantifiable weight, although, it can be argued that certain parameters, not studied, including mental well-being, discrimination, etc. due to, or as a result of, an inability to adapt or resistance to adapt, may be looked into.
In a study by Kobel et al. [37] performed on 525 school-aged children in Germany, which analyzed the effects of interventions to promote healthier diet and behaviors, the prevalence of overweight and obesity in those with a migration background was 11.8% and obesity alone 5.7% (vs 9% and 4%, respectively in German children [38]).
Also, the study by Early et al. [39] investigated the efficacy of an intervention aimed at improving health behaviors in 68 children (mean age 10.8 years) from low-income families enrolled from 3 clinic sites in California, USA. Most of the children had a migration background with 85% being of Hispanic origin and 3% Black/African American. The reported incidence of overweight was 11.8% and that of obesity 54.4%, very similar to the figures reported by the previously cited research from the USA.
Lane et al. [22] analyzed the health status of 300 immigrant and refugee children aged 3-13 years who had been in Canada for less than 5 years. The results indicated that older immigrant children (OR 1.18 (95% CI: 1.03-1.35); p = 0.017), mainly those from more privileged backgrounds, who coincidingly consumed a poorer-quality diet (OR 0.94 (95% CI: 0.90-0.99); p = 0.020), were at a higher risk of overweight and obesity (compared to refugees, who had a higher risk of stunting (23% vs 4.6%; p < 0.05)). Moreover, 52% of the newcomer children had high cholesterol levels and 29% had borderline or elevated blood pressure, higher rates compared to what reported for Canadian children (35% and 7% respectively).
Several studies analyzed the relationship between obesity and FI with conflicting results. The study by Distel et al. [41] considered the relationship between FI and chronic stress on BMI in 104 Mexican-American children aged 6-10 years. Greater food insecurity was associated with higher BMI only when children had high levels of hair cortisol (beta=3.50, p = 0.02), highlighting the great influence of stress on the development of overweight and obesity.
Buscemi et al. [42] confirmed a high prevalence of overweight and obesity among Latino children in the US: those with both immigrant parents had a higher (p = 0.03) mean BMI percentile (85.05, SD = 18.72) compared to those with non-immigrant parents (70.30, SD = 32.84). Furthermore, the mean BMI percentile of children from food secure families was significantly higher than that of children from food insecure families (p = 0.022), with acculturation being a significant moderator of the relationship between food insecurity and BMI. In fact, high acculturation and high food security scores were associated with lower BMI (p = 0.003).
Kilanowski et al. [43] published a cross-sectional study reporting that, among migrant farm-worker families in the US, low or very low levels of food security were seen in 48% of children with under or normal weight, 75% in overweight and 53% in obese children. However, differently from Buscemi and colleagues [42], no statistical significance was found between acculturation and BMI.
The role of acculturation on the development of childhood obesity in migrant children was also explored by other authors.
In a Swiss multidisciplinary lifestyle intervention study by Ebenegger et al. [44] preschooler children of migrant parents of low education backgrounds had an increase in adiposity (p ≤ 0.04) and media use (p ≤ 0.005) and less healthy habits (more consumption of fatty foods and less of fruit (p ≤ 0.0001), vegetables and water (p ≤ 0.03)) compared to those with non-migrant or medium-high educational level parents.
The study by Huang et al. [45] assessed the association between acculturation and body weight among the children (11-17 years) of internal migrants in China. The overall prevalence of overweight/obesity was 12.5% in boys and 6.1% in girls; migrant children who had urban-to-urban migrant caregivers were more likely to be overweight/obese than those with rural-to-urban migrant caregivers (OR 1.80 (95% CI: 1.13-2.86); p = 0.014), and those with caregivers having higher levels of acculturation (OR 0.99 (95% CI: 0.98-1.00); p = 0.078) were less likely to be overweight/obese than those with lower levels. However, there was no statistically significant difference in terms of acculturation score between overweight/obese and normal weight migrant children.
The effect of the length of stay in the new country was analyzed by two papers. Using data from the National Health and Nutrition Examination Survey, a cross-sectional study by Tsujimoto et al. [46] assessed the correlation between the length of time in the US and the prevalence of obesity in 28282 children and adolescents. The prevalence of overweight/obesity was lowest in those who were foreign-born and had been in the US for less than 1 year compared to the US-born (overweight or more: 23% vs 31.8%, obesity: 8.2% vs 16.9%, severe obesity: 2.9% vs 5.9%), with an increasing trend in foreign-born children who lived in US for more than 1 year (overweight or more: adjOR 1.38 (95% CI: 0.85-2.24), obesity: adjOR 1.80 (95% CI: 0.82-3.96), severe obesity: adjOR 1.36 (95% CI: 0.25-7.30)), suggesting that foreign-born children and adolescents are susceptible to the obesogenic environment of the USA with unhealthy dietary habits (high energy, sugar, and fat intake).
In the cross-sectional study by Iguacel et al. [47] about the association between social vulnerabilities and children' s weight status in Europe, children with a migrant background were more likely to be overweight/obese at the first evaluation (OR 1.30 (99% CI: 1.04-1.62); p = 0.003) and to remain so after 2 years (OR 1.14 (99% CI: 0.85-1.52); p = 0.239) compared to non-migrants. In this study the association between social vulnerabilities and children' s weight was only partially explained by lifestyle factors, maternal BMI and socioeconomic status indicators. Indeed, children who accumulated more vulnerabilities (migrant background, parents unemployed, non-traditional families, lack of a social network) did not show a higher likelihood of being overweight o underweight (OR 1.33 (99% CI: 0.91-1.94)).
Other studies investigated the role of healthy behaviors (physical activity, diet, and sleep quality) in the progression towards being overweight or obese in children with migrant backgrounds.
Labree et al. [48] reported a cross-sectional study including 1943 parent-child native Dutch and immigrant dyads. Children of migrant descent had higher BMIs and prevalence of overweight and obesity (p < 0.05); they had lower physical activity levels and lower sleep duration, but a higher fruit and vegetable intake and a lower consumption of sugar-sweetened beverages and energy-dense snacks (all p < 0.05). Less sleep, low fruit intake, and more energy-dense snack consumption correlated with higher BMIs and higher prevalence of being overweight and obese (all p < 0.05). Ethnic differences between native Dutch and migrant children only slightly contributed to explaining differences in the prevalence of being overweight and obese.
Also, the Swedish study by Besharat Pour et al. [49] assessed the nutritional status, level of physical activity, and overweight/obesity among children of immigrant or Swedish-born parents. Children of migrants were more likely to be overweight (OR 1.33 (95% CI: 1.07-1.66)), have low physical activity (OR 1.30 (95% CI: 1.05-1.62)) and have parents with the lowest education level compared to children of Swedish parents. However, children of immigrants complied more fully with nutritional recommendations compared to the Swedish (OR = 1.31 (95% CI 1.08-1.58]), even if they had a lower intake of micronutrients such as vitamins A (mean 1049.9 ug/day, SD = 366.6) and D (mean 5.1 ug/day, SD = 1.8), calcium (mean 1162.8 mg/day, SD = 348.6) and iron (mean 10.57 mg/day, SD = 1.83), and a higher consumption of sugar and sweets (p < 0.01).
Chomitz et al. [50] analyzed the associations between diet, physical activity and acculturation among Chinese American children. The prevalence of overweight and obesity, as reported by the parents, was higher (32%) among children of less acculturated parents, who were 3.5 times more likely to be overweight/obese than those from most acculturated families. However, after adjustment by age, gender and income proxy, acculturation status amongst migrant children was not a significant predictor of the child health outcomes.
The cross-sectional study by Alasagheirin et al. [51] highlighted some potential risks related to body composition and metabolic features in 64 Sudanese children living in the US: 26.6% were overweight or obese determined by BMI and 28% were obese determined by body fat percent; levels of cholesterol were borderline/high in 23.4%, triglycerides in 32.8%, and 16% had risk levels for insulin resistance. Food insecurity was reported by 40% of the families; moreover, the levels of physical activity in Sudanese children were very low and 42.2% of them spent at least 3 h a day watching television or using electronics devices.
Parental feeding styles may influence children' s eating habits and consequently their weight. This topic is highlighted by Tovar et al. [52] in a randomized controlled lifestyle intervention study that included 383 mother-child dyads of Brazilian, Haitian, and Latino peoples living in the US. 72% of mothers and 43% of the children were overweight and obese. A low demanding/high responsive feeding style in immigrant mothers (few rules, children were allowed much freedom) was significantly and positively associated with child weight status, even after adjusting for ethnicity, acculturation and stress (beta = 0.56, p = 0.01).
The relationship between immigrant parents' early life deprivation and child feeding practices and weight is treated by Cheah et al. [53]. Korean and Chinese immigrant parents of children aged 3-8 years in the US were interviewed about food insecurity, acculturation, child feeding practices, evaluations whether their child weight was more or less than the ideal and child consumption of soda drink and candy; BMI was calculated for parents and children. Even if only 20% of immigrant children were overweight or obese according to BMI, parents' FI in their childhood was associated with obesity-promoting behaviors and outcomes (beta = 0.17, p < 0.05).
The correlation between socioeconomic status and overweight/obesity was treated by Cook et al. [54] among seven Asian American ethnic groups. Adolescents from migrant families in the high-middle-level socioeconomic status ethnic group were less likely to be obese/overweight than those in the low-level (p < 0.01); this feature was not significant among US-born adolescents.
The cross-sectional analysis by Zulfiqar et al. [55] confirmed a higher trend of overweight/obesity in Australia for immigrant children from low-middle income countries (boys: 30%, 23%, 22%; girls: 35%, 22%, 24%; p = 0.002; for low-middle income countries, Australian-born and high-income countries respectively). The results show that the excess weight/obesity risk in this group is primarily due to sedentary activities (p < 0.01).

Stunting
In agreement with WHO definitions, stunting was defined as height-for-age-and-sex less than two standard deviations below the median.
Evidence for this outcome comes from 5 papers: 4 cross-sectional studies and 1 cohort study. Quality was classified as good for all of them. The majority of the studies assessed a remarkable stunting prevalence in migrant children, highlighting the need for specific screening and therapeutic programs. Alasagheirin et al. [51] conducted a cross-sectional descriptive study of skeletal growth in 64 Sudanese children aged 5-18 living in the US and found that almost 5% (4.69%) of them were abnormally slowed in growth, and girls were nearly twice as likely to be stunted than boys (6.06% vs.

3.23%, respectively).
Similarly, the study by Lane et al. [22] documented that the prevalence of stunted growth was 4.6% in 300 migrant children aged 3-13 years who had been in Canada for less than 5 years.
In 2011 Iriart et al. [56] investigated the prevalence of stunting in Hispanic children living in the US. Among 3102 children and adolescents aged 2-19 years, the prevalence of stunting was significantly higher (p < 0.001) in Hispanics (6.6%) than in non-Hispanic whites (2.2%). Normal weight foreign-born Hispanic children who had been in the US 5 years or more experienced the greatest prevalence of stunting, significantly higher than their counterparts who had been in the US for less than 5 years (25.7% vs. 11.9%, p < 0.01). Stunting prevalence did not significantly differ between normal weight and overweight/obese Hispanic children, but overweight/obese children with economic difficulties experienced a higher prevalence of stunting, compared to those who do not face adverse socio-economic conditions (p < 0.10). The proportion of stunting differed significantly by country of birth (14.1% for foreign-born vs 5.2% for US-born; p < 0.001), language of family interview (9.4% for Spanish vs. 5.6% for English; p < 0.05), and number of people in the family (10.5% for 6 or more members, 3.1% for 4-5 members, 7.7% for 1-3 members; p < 0.001). Moreover, also low educational level (p < 0.10) and low family income (p < 0.10) were found to be associated with stunting.
Choudhary et al. [57] assessed the prevalence of stunting in children below 3 years of age migrating to Mumbai from rural and urban areas of India. This paper showed a significantly higher incidence of stunting among rural migrants compared to urban ones (p < 0.05) and among migrants who came to Mumbai during the last five years compared to migrants who had been staying in Mumbai for longer (p < 0.05), supporting a positive effect of the length of residency on the level of malnutrition due to the migrants' capacity of adaptation into the new environment.
Evidence supporting a correlation between migration and stunting was also confirmed by Lee et al. [58], who analyzed 70 North Korean children between 6-15 years migrating to South Korea. Stunting, evaluated using the Korean Growth Chart, was significantly higher (p = 0.040) in North Korean children at the time of entry to South Korea (11.4%) than in South Korean children (1.0%), but interestingly, after an average length of stay of 2 years the prevalence of stunting decreased in migrating children (5.7%), but North Korean children were still shorter (p = 0.000), probably because linear growth deficits are slow to recover as overall nutritional status remains poor compared to peers without exposures to FI.

Early Childhood Caries
We found one good-quality, case-control study by Werneck et al. [59] evaluating the prevalence and risk factors of early childhood caries (ECC) in Portuguese-speaking children aged 48 months or younger and with at least one parent from Portugal, Brazil, Angola, Mozambique and the Azores migrating to Canada. One-third (35%) of the children recruited had ECC. The factors that correlated the most with ECC were family without dental insurance (adjOR 4.87 (95% CI: 1.85-12.82); p = 0.001), lack of a family dentist (adjOR 3.96 (95% CI: 1.34-11.70); p = 0.013), and frequency (≥2 vs <2) of snack consumption (adjOR 3.79 (95% CI: 1.32-10.83); p = 0.013). Subjects from low-income families were almost 4 times more likely to have ECC, and low parental knowledge of harmful feeding habits were linked to higher prevalence of ECC (OR 2.84 (95% CI: 1.27-6.33); p = 0.010). Also, parents' countries of origin and their age at the time of immigration were significantly associated with ECC: children of parents from non-European countries migrating to Canada had a higher occurrence of ECC (p < 0.026), and parents who migrated in their 20s or older were 2-4 times more likely to have a child with ECC than those who immigrated at younger age (p < 0.04). A person who immigrates when he or she is a child would be more exposed to positive oral health messages at school, and this is not the case for someone who immigrated as an adult. Surprisingly, oral hygiene history was not a factor influencing dental health.

Micronutrient Deficiency
Evidence for this outcome comes from 3 cross-sectional and 1 cohort studies. Quality was classified as good for 3 of them and fair for one. These studies reported a high prevalence of micronutrient deficiency in migrant children.
Vitamin D deficiency was evaluated by Vatanparast et al. [60], distinguishing between migrant and refugee children aged 6-11 years in Canada. They noted a mean serum 25 hydroxyvitamin D (25(OH)D) concentration significantly higher in non-immigrant children than in immigrant or refugees, with overall a vitamin D deficiency/inadequacy in 63% of migrants and 80% of refugees. The prevalence of calcium intake inadequacy was 74% in migrants and 77% in refugees, and of vitamin D intake inadequacy 81% in migrants and 97% in refugees. Female sex (Standardized Regression coefficient: −0.39 ± 0.11, p < 0.001), longer stay in Canada (Standardized Regression coefficient: −0.23 ± 0.11, p = 0.04), darker skin pigmentation (Standardized Regression coefficient: 0.24 ± 0.11, p = 0.027) and low vitamin D intake from food and supplement (Standardized Regression coefficient: 0.46 ± 0.11, p < 0.001) were found to be significantly associated with deficient vitamin D serum status. Both immigrant and refugee children had percentile height (mean ± SD) lower than the 50th. Height and serum vitamin D were found to be significantly related to the Total Body Bone Mineral Content (Standardized Regression coefficient: 0.13 ± 0.06, p = 0.047), which was low in 41.9% of migrant children and 35.9% of refugee children compared to threshold for age, sex, and ethnicity.
However, Saunders et al. [62] found no association between immigrant status and serum ferritin, iron deficiency and iron deficiency anemia in 2614 healthy children aged 12-72 months living in Toronto, 47.6% of whom had an immigrant family status. The median serum ferritin was 30 µg/L (IQR 19-39); 10.4% of the children had ID, and 1.9% had ID anemia. Older age (p < 0.001), male sex (p = 0.02), no or low cow's milk intake (p < 0.001), and shorter breastfeeding duration (p < 0.001) were significantly related to higher serum ferritin, while immigrant status was not related to lower levels of serum ferritin. Interestingly, a household income of £15 000-£29 999 was associated with a 24.1% increase in child serum ferritin compared to children from families with a higher household income (p = 0.002).
Kim et al. [63] analyzed dietary intakes and plasma concentrations of vitamin E, vitamin C, selenium and carotenoid in 29 non-supplemented Latino children aged between 4-8 years migrating to Nebraska, USA. They reported that the mean daily intake of vitamin E was lower than the Estimated Average Requirement (EAR) and Recommended Dietary Allowance (RDA), but none of the subjects consumed less than the RDA for vitamin C (25 mg/day), selenium (30 µg/day), and carotenoid according to the age. Vitamin E plasma concentration was insufficient in 31% to 69% of the subjects depending on the criterion used, while mean vitamin C, selenium, and carotenoid concentrations were indicative of adequacy.

Discussion
This systematic review assessed the association between migration, FI, and major diet-related morbidities in children using data from 28 studies, 26 of whom were observational (cross-sectional, and cohort) studies, while the two others were randomized controlled trials. All but 3 studies were classified as being of good quality (Table 7).
Overweight and obesity were the most investigated problems, but the results were sometimes conflicting, probably because of the different variables (different populations, SES, acculturation, lifestyles . . . ) that were taken into account by the single works. Most of the studies highlighted a higher prevalence of overweight/obesity in migrant than in non-migrant children [35,37,39,40,42,[47][48][49]. Obesity is linked to difficulties in social adjustment, low self-esteem, depression, and lower academic achievement [64,65], causing a significant reduction in the children's quality of life [66]). Moreover, overweight children are at a greater risk for remaining overweight in adulthood and for the development of chronic illnesses, such as diabetes and cardiovascular diseases [67], which increases premature mortality [68]. Indeed, high cholesterol levels, high triglycerides, and high blood pressure have been observed frequently in migrant children [22,51].
The increased risk of being overweight in children with a migration background is affected by multiple factors, such as maternal obesity [35,40], given that women commonly assume the primary responsibility for the care and feeding of children using familiar lifestyle behaviors [69], lower economic income [50,54,55], and male gender [40]. Indeed, boys, even if generally more active than girls, have been reported to consume fewer vegetables and more sweet drinks compared to girls of the same age and to watch television more hours per day [70], thus unbalancing the ratio between caloric intake and consumption. A lower level of acculturation has been found to be associated with a higher BMI [42,45,50], mainly if both parents were of low educational level [44]. This could be explained, according to other studies, by the fact that unhealthy eating behaviors and sedentary habits are more often observed in children from low educational level families [71,72]. Prevalence of overweight/obesity has been found to be lower in foreign-born children and in children living in the host country for less than 1 year [46,55]. This could be attributed to immigrant self-selection, meaning that the ones who migrate are the healthiest subjects who are able to endure a long and physically demanding journey and who, at the arrival in the host country, are in reasonably good health (the so-called "healthy immigrant effect") [73]. Interestingly, a convergence of migrant health levels to native health ones within approximately 10-20 years has been reported. [73] Moreover, we should consider that BMI is frequently low at the arrival, mostly because in the countries of origin there is not food over-consumption and, in particular, low consumption of fatty, sugary and processed food, that is instead high in the destination countries (although it is true that obesity is increasing worldwide and it is high in some middle-income countries such as Mexico) [74]. The increase in the prevalence of overweight and obesity over time in the host country among migrant children might be due to acquired environmental risk factors (i.e., western-diet, availability of low-cost high-sugar and high-caloric snacks and a sedentary lifestyle) combined with those from the country of origin (i.e., restricting physical activity [49,51], and cultural preferences for large body size as a proxy for wealth, health, or beauty) [75,76]. Furthermore, parent's early life deprivation in the countries of origin, where FI and under-nutrition could be significant and dangerous factors to impaired childhood health, has been reported to be associated with parenting behaviors that promote weight gain [77], due to their different perception of what a healthy child weight is [53].
FI appeared to be discordantly correlated to overweight. It could be hypothesized that a higher BMI is easily associated with FI [41,43], given the availability of low-cost energy-dense foods; members of food insecure families report overeating, when possible, foods they like and even dislike to compensate for periods of deficiency [78]. This link could also be explained by the limited knowledge, time and resources that low food-secure subjects experience to engage in healthful eating and physical exercise [79]. It is interesting that the FI-obesity link has been reported to be stronger among women than among children: mothers frequently sacrifice their food supply to ensure that children are food secure, and this is supported by the fact that only half of food insecurity families with children are also child food-insecure. [9]. In contrast, some authors noticed that more food secure migrant families have children with higher BMI than the food insecure ones [38]. Families who can afford to purchase high-cost food such as fruits and vegetables, could also afford to buy more food in general and consequently cause a major intake of calories in children [80].
We also found strong evidence of a link between migration and stunting [22,51,[56][57][58]. Stunting may reflect the cumulative effect of chronic malnutrition and not only under-nutrition [56] and it is associated with increased morbidity and mortality from infection, in particular, pneumonia and diarrhea [81], and short and long-term functional impairment, including poor cognition and educational performance in childhood, low productivity and low wages in adulthood [82]. Iriart and colleagues [56] showed a higher prevalence of stunting in overweight children living in families with economic difficulties compared to overweight children who do not experience such conditions, suggesting that being overweight often matches with a high-calorie but nutrient-poor diet. A shorter period of stay in the host country, a higher number of people in the family, being foreign-born, a low educational level, and socio-economic difficulties affect the prevalence of stunting [56][57][58]. As the years of stay increase, migrants incorporate to the new environment and progressively learn new habits, beliefs, and behaviors, [57,58] and this effect is even more valid in children born in the host country from migrant parents [56]. Probably, by being incorporated into the new environment over time, immigrants learn how to get better food and progressively improve their SES.
Concerning oral health, ECC was found to be more frequent in migrant children from low-income families, and with parents who migrate from non-European countries in their 20s or later. If untreated, ECC evolves to a more severe disease, which can lead to malocclusions, abscesses and pain [21] and can negatively impact on quality of life, nutritional status, and growth [83,84]. It has been also reported that dental problems, left untreated, can accelerate diabetes and cardiovascular disease complications and may be also associated with respiratory diseases and adverse pregnancy outcomes [85].
When migrants arrive in the host country, they face a dental health care system that is predominantly private [86] and most of them cannot access this care due to a lack of financial resources and because they are not covered by dental insurance [87]. Indeed, we found that the other factors that strongly correlated with ECC were family without dental insurance and the absence of a family dentist [59].
A lack of a balanced diet is the cause of micronutrient deficiency, most of all vitamin D deficiency and ID. Serum vitamin D concentration has been noted to be low in a high rate of migrants, due to an inadequacy of vitamin D and calcium intake, and this was significantly connected to low Total Body Mineral Content. Other risk factors include being of female gender and having dark skin pigmentation [60]. Women are usually at a greater risk than men due to religious practices stemming from various parts of the word, causing insufficient skin exposure to the sun. Furthermore, dark skin pigmentation reduces the quantity of vitamin D produced for a given amount of solar ultraviolet radiation, that is typically lower in high-income countries than in the countries of origin of most migrant people; moreover, light exposure in the host countries is often insufficient during wintertime. Inadequate levels of vitamin D prevent proper bone growth, which can lead to rickets in children [15]. Clinical manifestations of rickets include restlessness, irritability, frontal bossing, wide open fontanelles, skeletal signs (enlargement of costochondral junctions at 6-9 months of age), soft osseous border, teething delayed, profuse sweating, muscle flabby, and upper respiratory tract infections [88]. Skeletal consequences include stunting, developmental motor delay, and deformities. In severe cases, the development of hypocalcemia can lead to tetany, seizures, laryngospasm, cardiomyopathy, and even death [89]. In order to prevent serious disease, consumption of milk and alternatives, vitamin D-fortified food, and vitamin D supplements should be recommended, in addition to regular sun exposure which is also associated with less sedentary lifestyles.
Two studies focused primarily on ID. ID is strictly associated with an inappropriate diet [14], and severe and/or prolonged ID can evolve to anemia. Notably, preschool age children are at a higher risk because of their rapid phase of growth, leading to a rapid depletion of the iron stores when the intake is not sufficient. The occurrence of ID anemia is also adversely affected by intestinal parasitosis [90], whose prevalence has been reported to be around 20% in newly arrived migrants in an Italian study [91]. We found conflicting results that correlate ID to migration. Strong risk factors raised by these studies are low socio-economic status, high cow's milk intake which is frequently used because infant formulas are more expensive, and longer breastfeeding duration. Iron is an indispensable micronutrient in brain metabolism, and its deficiency can cause changes in the neurotransmitter homeostasis, decrease myelin production, decline synaptogenesis, and decline the function of the basal ganglia, which adversely affect the psychomotor development and mental capacity [92]. ID can also affect children's emotional and psychological behavior, and this is correlated with the modification in the metabolism of dopamine, GABA, hippocampal function and structure, and myelinization [93]. ID anemia is also implicated in the susceptibility to infections, mainly of the upper respiratory tract, which are more frequent and have longer duration in anemic than in healthy children [94]. Early identification of ID is important for preventing the potentially irreversible effects of long-term low iron stores, such as developmental delay, mostly in the fields of attention, motivation [95], stimulus encoding, and memory [96]. Preventative strategies involving parents' education about the consumption of naturally iron-rich and of iron-fortified foods since breastmilk weaning could be implemented, as well as the routine exclusion of parasitic infections that can impair iron intestinal absorption and contribute to ID anemia [97].
Most of the studies were performed in the USA, and not much is known about dietary-related problems in children migrating to other areas of the world. The link between overweight/obesity and migration to the USA, mainly in the Latino people, was reported by several authors. However, studies about diet-related morbidities and migration to other countries are scarce and diverse, so that no clear association could be found between specific diseases and migration to specific geographical areas other than Northern America. Moreover, the diverse data which were variably considered in the papers (SES, acculturation, various ethnicities, eating habits, lifestyles) made the studies very heterogeneous between each other and this might account for the, sometimes, conflicting results.
Unhealthy eating habits can undermine healthcare systems. Obesity starting from infancy will probably continue throughout adulthood, and lead to chronic diseases such as diabetes, hypertension, and cardiovascular diseases, which have a strong impact on our healthcare systems [98]. There is solid evidence that programs of screening and interventions could be effective to improve the health of migrant children [99,100]. Many pediatric scientific medical societies actively recommend universal screening for social determinants of health, including FI, in order to identify people at risk at a social level. Unfortunately, although tools to efficiently assess social determinants exist, they are still lacking comprehensiveness in providing a concise view of health in socially deprived populations [101][102][103][104][105]. Therefore, public health programs to evaluate the increased frequency of micronutrient deficiencies and diseases in these populations need to be promoted.

Conclusions
The present systematic review identified a clear association between migration and diet-related morbidities in children, the major risks being obesity and stunting due to chronic malnutrition. FI and frequently low levels of acculturation are important social determinants in migrant people, leading to the purchase of low-cost foods with poor nutritional value and the maintenance of bad food habits and incorrect lifestyles. However, most of the studies were performed in the USA, and not much is known about dietary-related problems in children migrating to other areas of the world; more work should be done to provide clear evidence for other potentially important morbidities in this group.
Health policies should take into account these areas of vulnerability, which might be addressed with specific screening and educational programs. Healthy policies play a key role to face childhood obesity and the related disease, but currently, they are still at an early stage and have no perceptible impact on this problem [106,107]. Governments need to implement regulations that make a healthy diet accessible and affordable for all, especially for the most disadvantaged populations at major risk of FI; such changes sound necessary to improve chronic disease prevention and control, from the perspective of the economic sustainability of healthcare [108]. Paying for primary prevention, mostly in childhood, often leads to an overall saving: "Pay now or pay (more) later" [109]. In the same way, integrating oral health into primary care could help increase access to preventive care, treatment, and promote overall health, for example implementing dental hygienists into primary care settings and educating primary care clinicians in the impact of oral diseases, trains them in risk assessment, and how to assimilate oral health preventive services into their practice [110].
Patient-centered care and engagement have been reported to lead to greater patient satisfaction,