Background Previous studies have found that a school climate of more heteronormativity is associated with adverse effects on the mental health of LGB students. Accordingly, our aim was to assess the association between lower LGB prevalence in schools and unhealthy weight-control behaviors among LGB youth. Methods A cross-sectional, multilevel study based in public high schools in the city of Olinda, Northeast Brazil. A multilevel logistic regression was performed, including 2500 adolescents

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... lled in 27 schools. The contextual variable was the prevalence of LGB youth in each school (as a proxy for heteronormativity in schools), while the outcome was unhealthy weight-control behaviors (fasting, purging, and taking diet pills). We controlled for socioeconomic characteristics (age, sex, receiving a family allowance), obesity, and self-reported happiness. Results Lower LGB prevalence in schools was associated with higher odds of engaging in unhealthy weight-control behaviors (OR: 1.5, 95%CI: 1.0, 2.2) among all youth, regardless of sexual orientation. No cross-level interactions between school context and individual characteristics were statistically significant. Conclusion Lower LGB prevalence in schools was associated with a higher risk of unhealthy weight-control behaviors in youth regardless of sexual orientation, which may reflect either the contextual influence of school climate, or may be due to residual confounding.