Bye-bye BMI? Tape may measure obesity better
Researchers say waist-to-hip ratio may paint better picture of fitness
By Linda Carroll
MSNBC contributor
Updated: 6:42 p.m. ET Aug 23, 2006
Just last week a study came out showing that being overweight wasn’t likely to kill you. Then yesterday, two more studies were published saying that by packing on only a few extra pounds, you could significantly increase your risk of premature death.
At first glance, these three studies might lead to considerable confusion — and a devil-may-care attitude towards weight gain.
But experts emphasize there’s no real doubt that obesity raises the risk of death as well as serious conditions like heart disease, stroke and diabetes.
The real question, says Dr. Donald Cutlip, an associate professor of medicine at the Harvard Medical School, is whether body mass index is a good measure to determine whether someone is overweight.
The conflicting studies, each based on BMI scores, point out flaws with the common measure, basically a comparison of height to weight.
New research shows that there’s a better, more informative way to figure out if you are overweight — the waist-to-hip ratio — and all it requires is a measuring tape.
Too buff, too old
The first salvo in the latest obesity debate popped up last week in the British journal The Lancet. The study found that among patients with heart disease, death was actually less likely if a person was overweight. And obesity appeared to be downright protective.
The authors of the study pinned the unexpected results on BMI.
“Rather than proving that obesity is harmless, our data suggest that alternative methods might be needed to better characterize individuals who truly have excess body fat,” said the study’s lead researcher Francisco Lopez-Jiminez of the Mayo Clinic College of Medicine.
Cutlip agrees that BMI can be way off, especially when it comes to assessing a particular individual. The commonly used measure can give a skewed result not only for fit body builders who come out with a high number because of the extra weight associated with muscle, but also for the elderly, who tend to have scores that underestimate obesity because they have so much less muscle.
When it comes to large population studies, the measurement usually works well because BMI does give the right answer when averaged across many people. There were other flaws with the Lancet study, Cutlip says.
Still, most of us aren’t taking our measurements as part of a big study. We’re simply trying to figure out if we’re at a healthy weight or not. And in that case, BMI may not be the best way to find that out.
Hipper measurement
The best way to predict heart attack risk and other obesity-related diseases is a measurement that divides the circumference of your waist by your hips.
If you’re a woman, the waist-to-hip ratio should come out as no more than 0.8. Men have a little more wiggle room: a healthy waist-to-hip ratio for them is 0.95.
This means, if your belly has bulged out enough to catch up to the size of your hips, you should start worrying about your heart, experts say.
That’s because abdominal fat is more likely than fat stored in other spots to lead to changes in hormone levels and to cause inflammation, which in turn leads to clogged arteries, says Dr. Gordon A. Ewy, a professor and chief of cardiology at the University of Arizona College of Medicine, and director of the school’s Sarver Heart Center. So, “fat on a woman’s hips doesn’t seem to increase risk, whereas a beer belly does,” Ewy says.
Fat stored in the belly "is the most dangerous type of fat in our bodies," explains Dr. William Castelli, director of the Framingham Cardiovascular Institute.
The waist-to-hip measurement is likely to catch people at risk for fat-related diseases who might otherwise think they were at a healthy weight, based on their BMI scores.
It’s quite possible to have an acceptable BMI and still have some belly paunch, says Dr. Louis Aronne, clinical professor of medicine at the Weill-Cornell Medical College and director of the Comprehensive Weight Control Program at New York Presbyterian Hospital.
Certain groups of people — those from Japan and south Asia, for example — tend not to become obese but can have an increased risk of heart disease from storing small amounts of fat around their waists, Aronne says. “You can be thin and still have too much fat,” he adds.
Linda Carroll is a health and science writer living in New Jersey. Her work has appeared in The New York Times, Newsday, Health magazine, Smart Money and Neurology Now.
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