Title of article:

A comparison of distribution curves of body mass index from Brazil and the United States for assessing overweight and obesity in Brazilian adolescents

Authors: da Veiga GV, Dias PC, dos Anjos LA.
Journal: Rev Panam Salud Publica, Aug 2001;10(2):79-85

Abstract

OBJECTIVE: To assess the validity of recommendations for use of the 85th and 95th percentiles of body mass index (BMI) of the population in the United States of America as a screening tool to assess overweight/obesity in adolescents. METHODS: We investigated the relation between BMI and percent body fat in 1,540 adolescents (717 males and 823 females) aged 10 to 17.9 years old from a private high school in Niteroi, a city in the state of Rio de Janeiro, Brazil. We used bioelectric impedance, with the appropriate equations for adolescents, to estimate percent body fat, which served as the gold standard (30% for girls and 25% for boys) to calculate the sensitivity and specificity of the 85th and 95th percentiles of the United States and Brazilian distribution curves of BMI. RESULTS: Sensitivity and specificity were high (above 80%) for the Niteroi boys, except for the 85th percentile of the Brazilian curve (specificity = 61.8%) and for the 95th percentile of the United States curve (sensitivity = 55.4%). For the Niteroi girls, the 85th- and 95th-percentile BMI cutoff points, from both the United States and Brazilian curves, showed low sensitivity, and that sensitivity decreased with age. Specificity was high for the girls, and much higher than it was for the boys. CONCLUSIONS: These data suggest that using BMI to screen for overweight/obesity in adolescents can generate a high percentage of false-positives for Niteroi boys and an even higher percentage of false-negatives for Niteroi girls. A more universal approach to using anthropometric measures to screen for overweight/obesity should be developed, preferably linked to stages of maturation.

Comments and Key points

This study measured body fat percentages, using the Tanita body fat monitor scale , which uses foot-to-foot bioelectric impedence technique. The sample population is Brazilian adolescents.

They used body fat percentages, 25% for boys, 30% for girls, as the threshold definition of obesity. ( This is commonly used for adults, but who knows if it's good for children. )

The article included data of mean body mass index (BMI), shown in the graph below for boys and girls.

Unfortunately, the article didn't show data for Brazilian 85th and 95th percentiles. It did show specificity and sensitivity data comparing Brazilian and USA thresholds, but that is not helpful to the reader, without the actual 85th and 95th percentile BMI values being shown. Thus, I found this article of little help.

If you read the abstract, their conclusion focuses on supposed flaws of USA criteria applied to Brazilian population. However, I think the flaw really is that their body fat thresholds (25% and 30%) are not suitable. (Especially 30% for judging obese girls). These threshholds came from adults.

My conclusion, is that the USA 85th percentile threshold for "overweight" is very slightly too low for boys age 10-14, but OK for older boys. The Girls USA 85th percentile threshold for "overweight" is OK for ages 10-14, but is too high for older girls. For "obese" thresholds, the USA 95th percentile is slightly too high for all (ages 10-18) boys. For Girls, the USA 95th percentile threshold is definately too high. ( For Brazilian adolescents, that is.) Perhaps the body fat definition of obesity at 30% body fat, is the problem. Perhaps it should be higher, like 33%.

 

Review & comments by Steven B. Halls, MD, Last modified 23-June, 2008, Copyright
See other scientific BMI articles.