Influence of country of birth and ethnicity on body mass index among Canadian youth: a national survey.

BACKGROUND

The body mass index (BMI) of youth often changes when they immigrate to a new country as a result of the adoption of new behaviours, a process called acculturation. We investigated whether BMI differs by country of birth (Canada v. other countries) and ethnicity, both individually and together. We also examined whether time since immigration and health-related behaviour explain any observed BMI differences.

METHODS

Data sources were the Canadian Health Behaviour in School-Aged Children study and the Canada Census of Population. Participants were youth in grades 6-10 (weighted sample n = 19 272). A questionnaire was used to assess participants' sociodemographic characteristics, height, weight and health-related behaviour. We calculated BMIs from participants' self-reported heights and weights and used World Health Organization growth references to determine BMI percentiles.

RESULTS

Based on self-reported heights and weights, BMI percentiles for foreign-born youth were lower than those of youth born in Canada (-4, 95% confidence interval [CI] -6 to -2). This difference did not decrease with time since immigration. Similarly, BMI percentiles were lower among East and Southeast Asian youth than their peers from the Canadian host culture (-4, 95% CI -6 to -2). Finally, BMI percentiles for foreign-born Arab and West Asian youth and East Indian and South Asian youth were lower than their Canadian-born peers of the same ethnicity (-14, 95% CI -22 to -7; -8, 95% CI -14 to -3).

INTERPRETATION

Immigrant generation and ethnicity were related to BMI among Canadian youth, both independently and together. Some ethnic groups showed differences by country of birth, i.e., East Indian and South Asian, while others showed no such difference, i.e., East and Southeast Asian. There was no association with time since immigration. Our findings reinforce the need to investigate country of birth and ethnicity when considering the determinants of childhood BMI.