Based on 2020 Census Bureau data, the percentage of people who reported multiple races changed more than all of the race alone groups, increasing from 2.9% of the population (9 million people) in 2010 to 10.2% of the population (33.8 million) in 2020. Yet, the majority of national health surveys aggregate all individuals who identify with multiple races into one heterogeneous group. We hypothesize this aggregation masks important differences in terms of health. Beyond the aggregation, there are multiple dimensions of race/ethnicity including racial self-identification (the race(s) one identifies with), racial category (the census category one selects), Hispanic ethnicity, and others that do not ideally overlap among multiracial adults. For multiracial adults, it is unknown how these multiple contexts of race and ethnicity intersect with one another. We evaluated the intersection of racial self-identification, racial category, and Hispanic ethnicity on body mass index (BMI) among multiracial adults as a second-level social identity strata. We then examined if these intersectional inequities in BMI were differently patterned in urban, suburban, and rural areas. We used multilevel analysis of individual heterogeneity and discriminatory accuracy (MAIHDA) among multiracial adults in the US (n=42,632) with a three-year (2010-2012) pooled sample of the Behavioral Risk Factor Surveillance System (BRFSS). We observed intersectional effects on BMI inequities. Most of the effects of social identity on BMI were explained by the combination of racial self-identification, racial category, and Hispanic ethnicity among multiracial adults (85.3%). Those living in a rural area had considerably higher BMIs than those living in an urban or suburban area. This is especially true for individuals with racial self-identification of White-Black, White-Native Hawaiian/Pacific Islander (NHPI), Black-American Indian/Alaska Native (AIAN), Asian-NHPI, and White-Black-AIAN and those who chose the racial category of NHPI. For example, individuals who self-identified as White-Black had an average BMI 4.5 kg/m 2 (p<0.01) higher in rural areas compared to White-Blacks living in urban areas. The magnitude of this BMI gap across urban-rural environments varied considerably across social identity strata ranging from 35.3 kg/m 2 among Non-Hispanic White-Black-AIAN with no preference for one race to 22.5 kg/m 2 among Non-Hispanic White-Asian with no preference for one race. This study highlights aspects of the social construction of race and patterning across the urban-rural divide in evaluation of BMI/obesity. This study brings to light inequities within people who identify as multiracial and highlights sub-populations to focus future policy and intervention research on.
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