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BMI in Identifying Excess Adiposity in Youth

J Pediatr; ePub 2016 Aug 2; Ryder, Kaizer, et al

While body mass index (BMI) correctly identifies adiposity in most youth with class 2 and 3 obesity, a relatively high degree of discordance was observed in youth with obesity and overweight, according to a recent study. Using dual energy x-ray absorptiometry (DXA) data from the National Health and Nutrition Examination Survey 1999 to 2006, 10,465 youth aged 8 to 20 years were studied for the analysis. Researchers found:

• Nearly all youth with class 3 obesity and a high proportion of those with class 2 obesity had excess adiposity.

• There was significant discordance between BMI characterization and DXA-derived excess adiposity among youth with class 1 obesity or overweight.

• Cardiometabolic risk factors are increased in the presence of excess adiposity, regardless of cutpoint used.

Citation: Ryder JR, Kaizer AM, Rudser KD, Daniels SR, Kelly AS. Utility of body mass index in identifying excess adiposity in youth across the obesity spectrum. [Published online ahead of print August 2, 2016]. J Pediatr. doi:10.1016/j.jpeds.2016.06.059.

Commentary: This study is an important addition to our understanding of how to interpret the most commonly used measure of adiposity, the BMI. While initially developed for population-based studies, BMI is now the most common descriptor of adiposity used in clinical practice. A BMI <18.5 is underweight, 18.5-25 is normal, 25-30 is overweight, 30-35 is obese (class I), 35-40 is obese (class II) and >40 is obese (class III). The current study extends the data already observed in adults and college students showing that BMI accurately correlates with adiposity among those who are very obese (class II and III), but is not an accurate predictor of lean and fat body mass in those who are overweight or with class I obesity.1,2Neil Skolnik, MD

1. Odde JJ, et al. Body mass index as a predictor of percent fat in college athletes and nonathletes. Med Sci Sports Exerc. 2007;39(3):403-409.

2. Romero-Corral A, Somers VK, Sierra-Johnson J, et al. Accuracy of body mass index in diagnosing obesity in the adult general population. Int J Obes (Lond). 2008;32(6):959–966. doi:10.1038/ijo.2008.11.