Obesity Thresholds Accurately Predict Adolescent Health Risk

Jenni Laidman

January 29, 2014

Body mass index (BMI) thresholds that identify adolescent obesity accurately predict metabolic health risk, according to a study published online January 27 in Pediatrics.

Kelly R. Laurson, PhD, assistant professor, School of Kinesiology and Recreation, Illinois State University, Normal, and colleagues categorized 3385 adolescents according to presence or absence of metabolic syndrome and by their BMI as established under 2 standards: one from the Centers for Disease Control and Prevention (CDC) and the other from FITNESSGram (FGram), a commercial physical fitness assessment program for youth. The researchers also identified optimal BMI percentiles for the detection of metabolic syndrome. The study data came from the National Health and Nutrition Examination Study (NHANES) database for 1999-2008. Participants ranged in age from 12.0 to 18.9 years.

The researchers found metabolic syndrome in 19% to 35% of obese adolescents compared with fewer than 2% of normal-weight peers. Compared with normal-weight peers, obese adolescent boys had a 46- to 67-fold greater risk for metabolic syndrome. Obese adolescent girls had a 19- to 22-fold increased risk for metabolic syndrome compared with normal-weight girls.

The researchers found that both CDC guidelines and FGram guidelines accurately predicted metabolic syndrome, although the CDC guidelines were slightly more predictive than FGram for boys, and FGram standards were slightly better for girls.

"I think the bottom line is that it's reassuring that our current approach to classifying kids either overweight or obese actually works pretty well," American Heart Association spokesperson Stephen Daniels, MD, PhD, told Medscape Medical News. Dr. Daniels is a professor and chairman of the University of Colorado School of Medicine Department of Pediatrics, Denver. Dr. Daniels, who was not involved in the study, is also pediatrician-in-chief, L. Joseph Butterfield Chair of Pediatrics, Children's Hospital of Colorado, Aurora.

He notes that the cut-off points for adolescent obesity "were not based on their relationship to outcomes. What you want, ultimately, is cut points that mean something in terms of risk of either having something [wrong] at that point in time or developing something new in the future." This study shows there is a relationship between thresholds and outcomes, and that the CDC guidelines and FGram guidelines are similar.

One Standard Would Be Best

FGram and the CDC have slightly different cut points for obesity. FGram, which is commonly used in schools, set the threshold for obesity at the 92nd percentile for boys and the 90th percentile for girls. Under the CDC standards, the threshold for obesity for both boys and girls is at the 95th percentile. In this study, children were said to have metabolic syndrome if they had 3 or more of the following characteristics: high waist circumference, elevated systolic or diastolic blood pressure, elevated triglycerides, high fasting glucose levels, or low high-density lipoprotein cholesterol.

About 7% of the adolescents in the study met the criteria for metabolic syndrome. Using the CDC obesity threshold, 35.4% of obese children had metabolic syndrome compared with 6.8% of overweight children and 0.8% of normal-weight children. Under FGram standards, 28.2% of obese children had metabolic syndrome, as did 2.7% of overweight children and 0.8% of normal-weight children.

The odds of metabolic syndrome for obese boys were 46.0 (95% confidence interval [CI], 19.5 - 108.4) times higher than those of normal-weight boys, using the FGram threshold. Using the CDC threshold for obesity, the odds of metabolic syndrome for an obese boy were 66.9 (95% CI, 27.9 - 160.4) times greater than those of normal-weight boys. For obese girls, the odds of metabolic syndrome were 21.6 (95% CI, 7.6 - 61.3) times higher than for normal-weight girls under FGram and 18.9 (95% CI, 6.3 - 56.2) times higher under the CDC threshold. With the CDC threshold, obese girls were at 3.2 (95% CI, 1.6 - 6.4) times greater odds of metabolic syndrome than overweight girls. There was no significant difference in odds for metabolic syndrome between obese and overweight girls using the FGram threshold.

Stephen R. Cook, MD, MPH, associate professor in the University of Rochester Medical Center School of Medicine and Dentistry in New York, told Medscape Medical News that it is important that pediatricians not overrespond to a child's BMI. "If there's an overweight kid, they should keep eating healthy and watch their screen time. If a child is obese, with high blood pressure, a bad family history, and he reports being teased about his weight, that's the kid I want to provide the right kind of emotional support and help for." Dr. Cook was not involved with the current study.

The authors conclude that the CDC thresholds were more diagnostically useful for boys, whereas the FGram thresholds were slightly better for girls. However, they write, a common standard would be best.

"Although the FGram standards are popular, especially for fitness testing, the CDC thresholds are already more widely used by pediatricians and those working in public health care. Therefore, we recommend using the CDC standards so that children and parents receive consistent messages about weight status throughout growth and maturation."

Dr. Welk is the scientific director for FGram and oversees the scientific advisory board. The other authors and the commentators have disclosed no relevant financial relationships.

Pediatrics. Published online January 27, 2014. Abstract

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