[Evolution of nutritional status in a cohort of school age children]

Considering the high prevalence of obesity among children attending elementary schools, it is important to know the evolution of body weight when these children reach adolescent.

To analyze the changes in nutritional status of children between the first year of elementary school and the first year of high school.

A historical cohort of children that were assessed when they started elementary school in 1997 was evaluated again eight years later Weight and height were measured and body mass index (BMI) was calculated. Obesity was considered as a BMI over percentile 95 of Center for Disease Control (CDC) references. The concordance between nutritional assessment in both periods and the risk of obesity during adolescence, based on previous weight were also calculated.

Data from 117,815 children were analyzed. The prevalence of obesity in the first year of elementary school and the first year of high school was 14.6% and 7%, respectively. The mean weight increase during the eight years period was 32.6+/-8.4 kg corresponding to 108%+/-28.1% of the expected increase. There was a low diagnostic concordance between both assessment periods. There was a reduction of under and overweight and a higher proportion of subjects with normal weight in the second assessment period. The risk for being obese in the first year of high school was 6.4 times greater for children that were obese in the first year of elementary school (confidence intervals 6.1-6.9.

There was an important reduction in the proportion of obesity between the age of 6 and 14 years. The risk of obesity at 14 years of age was strongly influenced by the presence of obesity at 6 years of age. The broader BMIranges for normality for high school children could give a false image of the nutritional status of teenagers .