Trends in height and BMI of 6-year-old children during the nutrition transition in Chile.

OBJECTIVE: We analyzed trends in height and BMI and their interaction in 6-year-old Chilean children over the last 15 years. RESEARCH METHODS AND PROCEDURES: We calculated height for age z-score (HAZ), BMI z-score, prevalence of obesity, underweight, and stunting from cross-sectional national school-based annual population surveys in 1987, 1990, 1993, 1996, 2000, and 2002. Using mixed model analysis, we determined the risk of obesity according to height over time as odds ratios (ORs) and 95% confidence interval and the potential influence of height and year of study on BMI z-score. RESULTS: Over the study period, height increased by 2.8 cm in boys and 2.6 cm in girls, whereas stunting declined from 5% to 2% in both. Tallness increased by approximately 2%, BMI z-score increased from +0.3 to +0.65 in boys and to +0.62 in girls, and HAZ increased from -0.47 in boys and -0.45 in girls to 0 in 2002. Underweight declined from 4% to 3%, whereas obesity rose from 5% to approximately 14%. The probability of obesity among tall children was significantly greater than that for normal height children (OR, 2.3 to 3.5). The lowest obesity risk was observed between -2 and -1 HAZ. The OR for obesity in the stunted relative to normal height children was variable, ranging from 1.23 to 0.65, whereas it was significant and consistently positive (1.1 to 1.7) for boys and girls when it was compared with the lowest obesity risk according to height. DISCUSSION: Tallness is significantly associated with increased obesity risk in children, while stunting is also associated, but to a lesser degree.