A shift in the epidemiology of low body mass index in Brazilian adults

Objective: To study the prevalence and current predictors of low body mass index (BMI) in a population undergoing a rapid nutritional transition. Design: Population-based cross-sectional study. Settings: Individuals living in the urban area of Pelotas, a medium-sized southern Brazilian city, were interviewed at home. Subjects: A multiple-stage sampling strategy was used. Out of 3372 eligible subjects, 3047 were interviewed. The study was restricted to adults (≥20y). Main outcome measure: Low BMI was defined as <18.5kg/m². Results: The prevalence of low BMI was 2.7% (95% confidence interval: 2.1; 3.3), higher in women than men (3.8 vs 1.3%; P<0.001). In the whole sample (men and women combined), living without a partner and current smoking were positively associated with low BMI. Among women, low BMI presented a U-shaped relationship with age and was positively associated with educational level. The prevalence of low BMI in young women was 6.3%, and in highly educated young women was 8.9%. Conclusions: Consistently with previous Brazilian studies, a decline in the overall prevalence of low BMI is clear. However, differently from these studies, the predictors of low BMI in women are similar to those observed within developed countries (including low age and high education), possibly indicating an increase in eating disorders.