Teens With Bulging Bellies at Increased Risk for Hypertension
Combining waist-to-height ratio with body mass index predicts the amount of fat floating in the blood and accumulated on bodily organs in teens.
Credit: Laborant | Shutterstock

Armed with nothing more complicated than a tape measure and a scale, researchers are perfecting the art of estimating levels of dangerous body fat in teenagers.

The technique simply combines measurements of body-mass index (BMI) and the waist-to-height ratio. The two measurements, which otherwise independently are imperfect probes of measuring body fat, surprisingly predict the amount of fat floating in the blood and accumulated on bodily organs, which ultimately can lead to diabetes, heart disease and cancers.

The dual method is an inexpensive proxy to body fat measurements using blood tests and whole body scans. Researchers from University of Toronto and the Hospital for Sick Children in Ontario, Canada, report these findings today (April 2) in the journals Archives of Pediatrics & Adolescent Medicine.

The problem with measurements

BMI, the ratio of a person's weight to height, is the most common measurement to determine whether a patient is overweight, yet it comes with numerous limitations: BMI cannot differentiate between lean muscle and unhealthy fat; it doesn't account well for different body-frame types, often categorizing short, chubby people as "healthy weight" and tall, muscular people as "overweight;" and it can be a poor indicator of obesity in teenagers, who are growing rapidly.

Waist circumference can be more predictive of abdominal fat, which is generally unhealthy and indicative of fat accumulating on organs such as the liver, kidneys and heart. A person can have a large frame with a large waist, however, and not have excess visceral fat on the organs. Regardless, waist circumference — essentially one's pants' size — rarely is measured during a medical exam.

Faced with the limitations of BMI, the Canadian researchers decided to examine the added role that waist measurements can have in predicting fat levels and subsequent health risks. They examined more than 3,000 teens ages 14 to 15 in Ontario, collecting waist, height and weight measurements along with blood pressure and blood samples.

For obese teens in particular, a high BMI coupled with a large waistline was associated with high blood pressure and high levels of circulating fat in the blood. Increases in waistline were directly correlated with increases in blood pressure and internal fat. These adolescents are at risk for diabetes and liver and heart disease, the researchers said.

Obese and overweight children with moderate waistlines had only slightly elevated fat levels. Those who had BMIs in the normal to overweight range, but had normal waist measurements, had healthy blood pressure and no excess levels of circulating fat.

Contention among researchers

Despite their simplicity, BMI and waistline measurements are the subject of much contention. Some researchers desire to eliminate them from the vernacular, claiming they are of little value to individuals wondering if they are overweight. BMI, for example, was a tool first used for population studies and only recently became associated with individual dieting goals and a healthy weight range. [5 Diets That Fight Diseases]

Data presented at the 2009 Endocrine Society annual meeting, from the University of Tennessee Health Science Center in Memphis, suggests that BMI and waistline measurements overestimate obesity among African-Americans. A paper published in August 2011 in the Journal of Adolescent Health stated that waist circumference was not a predictor of diabetes risk and shouldn't be collected.

Other papers have compared the predictive powers of one measurement over another, be it BMI, waist circumference or to the waist-to-height ratio.

This latest Canadian study, led by Michael Khoury of the University of Toronto, is among the first to look at how simple measurements of weight, height and waistline can complement each other. The sum is greater than the parts, the researchers concluded, and they recommend that the basic measurements become routine in medical exams.

The researchers hope to expand their analysis with a larger sample size to better represent race, body types, age and puberty stage.

Christopher Wanjek is the author of the books "Bad Medicine" and "Food At Work." His column, Bad Medicine, appears regularly on LiveScience.