Results: Over the 1992 and 2002 period, minimal changes were observed in the prevalence of overweight (from 1.4% (95% confidence interval (95% CI): 1.0-1.8) to 1.8% (1.6-2.0)) and underweight (from 32.1% (30.4-33.7) to 33.5% (32.8-34.1)) among 2-17 year-olds. In contrast, among 18-65 year-olds, the prevalence of overweight and obesity increased (from 2.0% (1.5-2.4) to 5.2% (5.0-5.4)) and underweight declined (from 32.6% (31.2-33.9) to 24.8% (24.3-25.3)). Urban residents experienced larger reductions in underweight and increases in overweight than rural residents. Analyses of BMI levels for the 15th, 50th and 85th percentiles, by age, revealed a trend of increasing BMI that was higher among adults, females and urban residents. Conclusion: Although underweight remains the main concern, overweight is an emerging problem in Vietnam. Early prevention is needed to prevent overweight from causing undesirable effects on health and economic in the transitional period. Sponsorship: Vietnam Educational Foundation (VEF) and the National Institutes of Health (NIH R01-HD30880 and R01-HD38700).

Background: No nationally representative data from middle-and low-income countries have been analyzed to compare the prevalence of underweight and overweight, defined by using the Centers for Disease Control and Prevention (CDC) and the International Obesity TaskForce (IOTF) body mass index cut points. Objective: To examine the consistency in the prevalence of underweight and overweight, defined by using the CDC and IOTF cut points in Chinese, Indonesian and Vietnamese children. Methods: We used data from 1600 Chinese, 11 756 Indonesian and 53 826 Vietnamese children aged 2-18 years, who participated in three recent, representative surveys in China, Indonesia and Vietnam. A smaller difference between prevalence and a higher k-statistic indicated a higher consistency level. Results: The prevalence of underweight was higher with the IOTF than the CDC cut points; absolute differences in the Chinese, Indonesian and Vietnamese were 6, 10 and 13% (boys), and 10, 13 and 19% (girls), respectively. The prevalence of overweight was more consistent (absolute differences were o2%, except for the 2-5.9-year-old Chinese and Indonesian children (from 2 to o5%)). Values of k-statistic (from 0.55 to 0.88) varied by age, sex and ethnicity. The consistency was gradually improving from the Vietnamese to Indonesians and to Chinese boys and girls, from girls to boys, from the younger to older boys and from the older to younger girls. Conclusions: The age, sex and ethnic differences in the prevalence of underweight and overweight suggest a systematic evaluation of the cut points.