Foreign-born youth have a lower body mass index (BMI) than Canadian-born youth and, contrary to current thinking, these differences did not disappear in the years after immigration, according to a study of Canadian youth in CMAJ Open. BMI also varied by ethnicity, with East and Southeast Asian youth having a lower BMI than Canadian "host culture" youth.
"The most important finding of this study was that the BMI of foreign-born youth was lower than that of their Canadian-born peers, and that this association was not linear with time since immigration," writes Atif Kukaswadia, Department of Public Health Sciences, Queen's University, Kingston, Ontario, with coauthors. "This goes against the theory of acculturation."
The study looked at data on 19 272 youth in grades 6 to 10 from the 2010 Canadian Health Behaviour in School-Aged Children (HBSC) study. Students from 436 schools in 8 provinces and 3 territories in Canada (New Brunswick and Prince Edward Island did not participate) provided information for the larger study. Survey questions asked about country of birth, length of time in Canada, ethnicity and lifestyle habits such as time spent watching TV or using electronics, snacking and fast-food consumption.
The researchers categorized youth into the following ethnic groups: Canadian host culture (European, North American and Aboriginal), the majority at 78.2%; Arab and West Asian (1.6%); African (3.8%); East Indian and South Asian (2.9%), East and Southeast Asian (5.7%); Latin American (1.0%) and Other (6.9%) (mixed ethnicity.)
Foreign-born youth had a BMI 4 percentile points below Canadian-born youth, and youth of East Indian/South Asian and East/Southeast Asian backgrounds had BMIs 4-5 percentile points lower.
"We were surprised to find that BMI did not change linearly with increased time since immigration," write the authors. "As in previous research of adults in Canada and the United States, we anticipated that differences in BMI would disappear over time. However, this was not the case, and we observed the opposite relation in our sample."
The authors suggest methodological inconsistencies, such as self-reporting of weights and height, and selection bias of youth could be behind this unexpected finding.
"For those in public health, our findings stress the importance of considering both ethnicity and country of birth when designing and implementing weight-loss interventions. Given the high proportion of Canadians who are immigrants, uncovering reasons for weight gain will lead to a better understanding of the determinants of childhood BMI," the authors conclude.