BMI in children

Body mass index (BMI) facilitates meaningful comparison of the weights of children of varying heights. It is useful in population studies, providing a measure of “fatness” that can be easily plotted and compared. However, for determining whether an individual child is obese, visual inspection—even from a distance of 30 yd—is superior to calculating his or her BMI. It might be argued that BMI does have one useful application in the clinical care of children: that is, it may be a more reliable indicator than visual inspection of progress made by a still-growing obese child whose weight control efforts are being monitored. Nonetheless, given that treatment of childhood obesity is so seldom satisfactory, even this use seems of negligible value.
—— John DiTraglia, MD
Portsmouth, Ohio

You raise the question of whether we should limit use of BMI in children to population studies and simply use inspection as our screening tool, particularly since intervention is relatively unsuccessful.

I would like to point out that there is no documentation that visual inspection clearly and reliably identifies those children who are obese, especially at mild levels of obesity. In fact, at least 1 study documents misperception by physicians of about one-third of children.¹ Certainly, studies have established that parents have only a limited ability to identify that their child is obese.^2-4 Moreover, as you point out, BMI is an excellent tool for tracking results of weight management efforts and can thus serve as both a learning tool and a monitor of progress for child and family alike. This is particularly helpful in the treatment of young children and of those who are merely overweight, in whom the goal may not be weight loss but weight maintenance as they grow in height.

weight maintenance as they grow in height. In addition, screening for comorbidities is, in part, a function of a child’s overweight status. Children with a BMI just above the 85th percentile, who are classified only as overweight, need cardiovascular and, in some cases, diabetes risk screening.^5,6 These children are easily misclassified on visual inspection.1 I, therefore, strongly urge physicians to use BMI and growth charts to determine by objective criteria who may need further screening for comorbidities as well as counseling regarding reduction in BMI.
—— Ilene Fennoy, MD, MPH
Clinical Professor of Pediatrics
Columbia University, New York