Why do flags flap on a windy day?
Believe it or not, this is just one of many questions science cannot surely resolve. There are others: What is gravity? Why do we dream? How many species inhabit our planet? Why is it that the freeway lane I choose is always the slowest? (Okay, in all fairness, I really doubt if scientists spend much time on the last question.)
Each of us has unanswered questions.
Since my field is health, I’ve often wondered why is it that we determine someone’s correct weight based on the Quetelet Index of Obesity, a formula dating back to nineteenth-century Europe? Granted, about a century later we shifted to Body Mass Index (BMI), which is weight divided by height squared. Yet the main premise remained in tact: how tall you are is virtually the sole factor to determine how much you should weigh.
That has never made sense to me. Why would a 5’ 6” forty-four year old vegan woman who enjoys yoga and jogs with regularity; and a sedentary man of equal stature who scarfs red meat, French fries, and drives his car 100 yards to the corner store; be considered healthy at the same weight? I have always thought something’s messed up.
It appears I’m correct – but I take no comfort in what I found out.
A recent study found that the BMI misclassified 39 percent of Americans. Instead of being “overweight,” it turns out they were more accurately “obese.” This is because BMI doesn’t distinguish between fat and muscle, and some folks with “normal BMIs” may harbor dangerously high amounts of fat in their bodies. Without an accurate measurement of how much body fat, the researchers say, millions of people don’t know they are at high risk for a number of obesity-related diseases such as heart disease and cancer, among others.
Dr. Eric Braverman, co-author of the study, points out
“Without knowing how much fat you have, you can't really save people from illness. It is the number one predictor of who's going to live or die.”
This new method of determining who is healthy is revealing some frightening stats. Of the almost fourteen hundred people studied, 26 percent were classified as obese using their BMI. That number almost tripled to 64 percent when measured with a Dual Energy X-ray Absorptiometry (DXA) scan, which is commonly used to check for osteoporosis, measure percentage of body fat, muscle mass, and bone density.
The study discovered that misclassifications were more common in women then men and also increased with age. For example, among women in their fifties, 48 percent more were classified as obese using the DXA instead of their BMI. For women over 70, it climbed to 59 percent. This is because as women age, they lose more muscle to fat than do men. Since BMI does not distinguish between muscle and fat, their classification of “obese” instead of “overweight” — or “even healthy” — would go unnoticed.
Braverman and his co-author Dr. Nirav Shah, are suggesting that we lower the definition of obesity to include more people. Currently, “obese” means a BMI of 30 or above. They recommend dropping that to 24 for women and 28 for men. To put that in perspective, under present standards, a 5’ 6” woman is considered healthy at 150. Under these new guidelines, she would be considered obese. (Ouch!)
Just when we thought we were starting to turn the corner on the fight against obesity, it looks like we have a lot farther to go.
Wednesday, April 04, 2012
Why do flags flap on a windy day?