Body mass index cutoff points for evaluation of nutritional status in Brazilian children and adolescents.

OBJECTIVE To delineate a classification system, comprising reference curves and cutoff points, based on the distribution of body mass index (BMI) across a national reference population and designed for the assessment of the nutritional status of Brazilian children and adolescents. METHODS Data from 13,279 males and 12,823 females aged from 2 to 19 years, extracted from the National Nutrition and Health Survey dataset (1989), were used to construct a reference curve. The LMS method was employed to calculate the BMI curve parameters and polynomial functions were used to model these parameters against age. The cutoff values for classifying nutritional status as underweight, overweight and obese were expressed as centiles and BMI values equivalent to 17.5, 25 and 30 kg/m(2) at 20 years, respectively. RESULTS Values for the L, M and S parameters were tabulated at 6-month intervals for each sex. Using these values, a graph was plotted with nine BMI distribution reference centiles. Cutoff values were presented that are equivalent to BMIs of 17.5, 25 and 30 kg/m(2) at the start of adulthood. CONCLUSIONS The classification system presented here can be used for clinical and epidemiological assessments, it is methodologically similar to the majority of national curves that have been presented to date and, furthermore, it offers a definition of underweight.