The poor stay thinner: stable socioeconomic gradients in BMI among women in lower- and middle-income countries.

BACKGROUND: Recent studies have shown a strong positive association between individual BMI (in kg/m(2)) or overweight prevalence and socioeconomic status (SES) in low- and middle-income countries (LMICs). However, it is not clear whether this association is weakening or reversing over time. OBJECTIVE: With the use of nationally representative data collected at 2 time points in 37 LMICs, we compared the associations of SES with BMI and of SES with overweight between the earlier surveys and the later surveys. DESIGN: We conducted a cross-sectional analysis of nationally representative samples of 547,056 ever-married nonpregnant women aged 15-49 y: 208,570 women in the earlier round of surveys conducted between 1991 and 2003 and 338,486 women in the later round conducted between 1998 and 2008. We used linear and modified Poisson analyses with a country fixed effect to obtain a pooled estimate and a country-stratified analysis for country-specific estimates. RESULTS: In adjusted models, BMI was 2.32 units higher (95% CI: 2.23, 2.41 units) among women in the wealthiest quintile compared with women in the poorest quintile in the earlier surveys and was 3.00 units higher (95% CI: 2.92, 3.07 units) in the later surveys. The association between BMI and wealth was positive in 37 countries in the earlier round of surveys and in 36 countries in the later round. Patterns were similar for overweight prevalence. CONCLUSION: The association between SES and BMI or overweight is positive in most LMICs and has not weakened over time. It appears that the burden of overweight is consistently greater among wealthier populations within LMICs