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BMI test underestimates obesity in teens with disabilities, research shows

July 2, 2015

Findings appear in a paper published June 9 on the website of the American Journal of Physical Medicine & Rehabilitation, the journal of the Association of Academic Physiatrists.

Obesity is a major problem in children and adolescents with mobility limitations, but standard assessments tend to underestimate it, according to the new research by Brooks C. Wingo, PhD, an associate scientist at the University of Alabama at Birmingham, and colleagues. The researchers suggest new cutoff points are needed for identifying disabled teens who might need diagnosis and treatment to prevent health and functional problems because of excess body weight.

What is the best measure?

The study included 29 adolescents (ages 14-17) who had spinal cord injury or other types of physical disability and used a wheelchair to get around. The researchers assessed various clinical indicators of body weight — not only BMI (calculated from height and weight), but also the width of a skinfold pinched in the upper arm (triceps) and circumferences of the waist, arm and leg.

A procedure called dual-energy X-ray absorptiometry also was done to measure the patients’ percentage of body fat. For the study, obesity was defined as 30% or greater body fat for males and 35% or greater for females. The various clinical measures were evaluated as indicators of obesity, as objectively determined by DXA.

As in previous studies, many of the teens who have a physical disability were obese. The findings showed 35% of boys and 58% of girls met the DXA criteria points for obesity.

However, if assessed by BMI alone, many of the patients would be misclassified as nonobese, the researchers found. Based on the standard BMI cutoff point of 95th percentile or higher for their age, only 6% of boys and 42% of girls were classified as obese. Because they still are growing, the adult BMI cutoff point of 30 or higher isn’t appropriate for assessing obesity for children and adolescents, according to the researchers.

All of the clinical measures were significantly correlated with body fat among the teens with disabilities. The best-performing measure was BMI, using a cutoff point of 20 for boys and 19 for girls. The second-best measure was waist circumference, with cutoff points of 83 centimeters (about 33 inches) for boys and 78 centimeters (about 31 inches) for girls.

Children and adolescents with physical disabilities are at high risk for obesity, the authors wrote. In addition to health issues such as diabetes and heart disease, obesity puts disabled youth at risk of a wide range of other problems, such as pain and depression, and might limit further their independence and mobility.

But it can be challenging to assess obesity and overweight in people with disabilities, and especially in children and adolescents, the authors wrote, and while DXA is a more reliable test for measuring body fat, it’s not practical for everyday clinical use.

The exploratory study confirms existing cutoff points underestimate obesity in adolescents with physical disabilities. It also provides a first step toward developing alternative assessments of obesity in this group of patients, although further research will be needed to confirm and validate the proposed alternative measures. Wingo and co-authors also call for the development of disability-specific cutoff points, which they wrote “will allow clinicians to better identify children at risk of adiposity-related diseases and offer parents preventive strategies to improve the health and quality of life of their children.”

(Source: blog.todayinot.com)


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