ORIGINAL COMMUNICATION A shift in the epidemiology of low body mass index in Brazilian adults PC Hallal 1 *, JCK Wells 2 , AD Bertoldi 1 , FK Gazalle 3 , MC Silva 1 , MR Domingues 1 , MLV Carret 1 , CLP Arau ´ jo 1 and DP Gigante 1 1 Post-graduate Program in Epidemiology, Federal University of Pelotas, Pelotas, Brazil; 2 MRC Childhood Nutrition Centre, Institute of Child Health, London, UK; and 3 Psychiatry Research Unit, Post-Graduate Psychiatry Program, Federal University of Rio Grande do Sul, Porto Alegre, Brazil 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 (Z20 y). Main outcome measure: Low BMI was defined as o18.5 kg/m 2 . 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%; Po0.001). 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. European Journal of Clinical Nutrition (2005) 59, 1002–1006. doi:10.1038/sj.ejcn.1602204; published online 22 June 2005 Keywords: body mass index; chronic energy deficiency; nutritional transition; nutritional status, underweight Introduction There is now substantial evidence that individuals with low body mass index (BMI) have poorer health and reduced physical work capacity (James, 1994). Women with low BMI are also more likely to have a low birthweight infant (Shetty & James, 1994). Low BMI might be attributed to a negative energy balance due to (a) insufficient energy intake; (b) voluntary decrease in food intake or voluntary increase in activity level in order to manipulate weight status. The first pathway is typical of developing countries, where lack of food still plays a significant role. The second pathway is typical of developed societies, where eating disorders are a current public health problem. Brazil is undergoing a rapid nutritional transition. The prevalence of adult low BMI was significantly reduced between 1976 (10%) and 1996 (5%), indicating success in tackling adult malnutrition (Monteiro et al, 2002). As in many countries, this reduction in low BMI has been accom- panied by an increasing prevalence of adult overweight and obesity (De Vasconcellos, 1994; Monteiro et al, 2002). The variables typically associated with eating disorders are not consistent with those related to chronic energy deficiency. Eating disorders are more frequent among Received 1 October 2004; revised 11 April 2005; accepted 13 May 2005; published online 22 June 2005 *Correspondence: PC Hallal, Post-graduate Program in Epidemiology, Federal University of Pelotas, Brazil, Duque de Caxias, 250, Third floor, 96030-002, Brazil. E-mail: prchallal@terra.com.br Guarantor: PC Hallal. Contributors: PC Hallal, AD Bertoldi, FK Gazalle, MC Silva, MR Domingues and MLV Carret coordinated the field work and performed quality control. PC Hallal and AD Bertoldi led the analysis process. JCK Wells led the writing process. CLP Araujo and DP Gigante worked as supervisors in all phases of the study. PC Hallal had the original idea for this paper. All authors helped in the writing and analyses processes, and approved the final version of the manuscript. European Journal of Clinical Nutrition (2005) 59, 1002–1006 & 2005 Nature Publishing Group All rights reserved 0954-3007/05 $30.00 www.nature.com/ejcn