Introduction To determine if food insecurity was associated with a higher prevalence of obesity in a large random sample of Brazilian women of reproductive age.

Methods The data were derived from the third edition of the Children's and Women's National Demographic and Health Survey, conducted in 2006–2007. This was a nationally representative cross-sectional study. Obesity (BMI≥30 kg/m²) was the outcome variable. Associations were measured using crude and adjusted prevalence ratios (PR) with 95% CI through Poisson regression models taking into account the complex sampling design. The sample included 10 226 women from 18 to 45 years.

Results The prevalence of any level of food insecurity measured by the Brazilian Food Insecurity Scale was 40.9%, with 25.5% light, 10.1% mild and 5.3% severe food insecurities. The prevalence of obesity was 17.4%. We found borderline effect of light food insecurity and increased prevalence of obesity in Brazil (PR=1.16; 95% CI 0.98 to 1.38; p>0.05). Women with mild food insecurity had a higher risk of being obese than their counterparts without food insecurity (PR = 1.49; 95% CI 1.17 to 1.90; p=0.010), after adjustment for skin colour/ethnicity, years of schooling, macro-region, income, age and marital status.

Conclusion Mild food insecurity was associated with obesity as measured by BMI, even after adjusting for various confounding factors in this large cross-sectional survey performed in a middle-income country undergoing the nutrition transition.