Background This research forms part of a cross-country comparison study that seeks to understand the role of ethnicity in framing childhood obesity as a public health problem. In our modern multi-ethnic world the need and opportunity for international comparisons using the concept of race and ethnicity are both becoming increasingly important. However, definitions of ethnicity vary according to socio-political circumstances. In preparation for conducting the major study, we have examined this concept in Colombia, Brazil, Mexico, Canada and the United Kingdom. Our research questions were: 1) How are ethnicity and race defined and measured? 2) What are the concepts that underpin race and ethnicity in each of the countries? 3) Are these measures, categories and concepts sufficiently similar to allow cross-country comparisons in the field of childhood obesity?

Methods We conducted a scoping review according to Leva et al. (2012). We searched published and unpublished literature, census questionnaires, and health and nutritional surveys, without restriction of language and reported from 2005. Starting from 2005 allowed us to include the latest Colombian census and the recent censuses and surveys from the other countries. We searched web pages from Ministries of Health and statistical agencies, electronic databases (CINAHL, Medline, EMBASE, Global Health Library and LILACS). We manually searched bibliographies of relevant books on ethnicity and health.

Results We reviewed 13 questionnaires, 4 constitutional acts, 8 official reports and their related documents. We found that all of the reviewed countries use self-identification to determine ethnicity. However, each country collects their data differently, using either a single concept of ethnicity or a combination of concepts. Colombia is focused on ethnic minority populations. Mexico, Canada and the UK use a combination of country of origin, geographical origin and skin colour. Brazil establishes ethnicity on skin colour alone. Canada has one White and Black categories while the UK evaluates a wider set of subcategories. England and Wales separate Irish from British and Scotland separates Scottish from British and Irish. Black categories in the UK also include African and Caribbean origin separately.

Conclusion As a result of this scoping review we identified different approaches to ethnicity which do not allow direct quantitative comparison. Therefore, our cross-country comparison study will be focused on understanding childhood obesity within each country, comparing qualitatively. Brazil is no longer considered a useful comparison given its singular approach. This kind of conceptual analysis is necessary for cross-country studies, and could lead to more international harmonisation of exposure variables such as ethnicity and race.